Kepler space telescope

The Kepler space telescope was part of NASA's Discovery Program of relatively low-cost science missions. The telescope's construction and initial operation were managed by NASA's Jet Propulsion Laboratory, with Ball Aerospace responsible for developing the Kepler flight system.{{Cite press release |date=March 6, 2014 |title=Ball Aerospace Kepler Satellite Marks Five Years of Planet Hunting |url=https://spacenews.com/ball-aerospace-kepler-satellite-marks-five-years-of-planet-hunting/ |url-status=live |archive-url=https://archive.today/20241021170558/https://spacenews.com/ball-aerospace-kepler-satellite-marks-five-years-of-planet-hunting/ |archive-date=October 21, 2024 |access-date=July 25, 2024 |publisher=Ball Aerospace & Technologies |via=SpaceNews }}

In January 2006, the project's launch was delayed eight months because of budget cuts and consolidation at NASA. It was delayed again by four months in March 2006 due to fiscal problems. During this time, the high-gain antenna was changed from a design using a gimbal to one fixed to the frame of the spacecraft to reduce cost and complexity, at the cost of one observation day per month.{{Cite book |last1=Taylor |first1=Travis S. |url=https://books.google.com/books?id=Scd0CwAAQBAJ&dq=kepler+high-gain+antenna+gimbal+fixed&pg=PT251 |title=A New American Space Plan |last2=Osborn |first2=Stephanie |date=2012-11-15 |publisher=Baen Publishing Enterprises |isbn=978-1-61824-961-6 |language=en}}

The Ames Research Center was responsible for the ground system development, mission operations since December 2009, and scientific data analysis. The initial planned lifetime was three and a half years,{{Cite news |date=March 7, 2009 |title=Nasa launches Earth hunter probe |url=http://news.bbc.co.uk/2/hi/science/nature/7926277.stm |url-status=live |archive-url=https://web.archive.org/web/20231207072112/http://news.bbc.co.uk/2/hi/science/nature/7926277.stm |archive-date=December 7, 2023 |access-date=March 14, 2009 |work=BBC News }} but greater-than-expected noise in the data, from both the stars and the spacecraft, meant additional time was needed to fulfill all mission goals. Initially, in 2012, the mission was expected to be extended until 2016,{{Cite news |last=Wall |first=Mike |date=April 4, 2012 |title=NASA Extends Planet-Hunting Kepler Mission Through 2016 |url=https://www.space.com/15160-alien-planet-kepler-mission-2016.html |url-status=live |archive-url=https://web.archive.org/web/20240715173315/https://www.space.com/15160-alien-planet-kepler-mission-2016.html |archive-date=July 15, 2024 |access-date=May 2, 2012 |work=Space.com }} but on July 14, 2012, one of the four reaction wheels used for pointing the spacecraft stopped turning, and completing the mission would only be possible if the other three all remained reliable.{{Cite news |last=Clark |first=Stephen |date=October 16, 2012 |title=Kepler's exoplanet survey jeopardized by two issues |url=https://spaceflightnow.com/news/n1210/16kepler/ |url-status=live |archive-url=https://web.archive.org/web/20240616190725/https://www.spaceflightnow.com/news/n1210/16kepler/ |archive-date=June 16, 2024 |access-date=October 17, 2012 |work=Spaceflight Now }} Then, on May 11, 2013, a second one failed, disabling the collection of science data{{Cite press release |date=May 21, 2013 |title=Kepler Mission Manager Update |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20130521.html |url-status=dead |archive-url=https://web.archive.org/web/20230711172415/https://www.nasa.gov/mission_pages/kepler/news/keplerm-20130521.html |archive-date=July 11, 2023 |access-date=June 14, 2013 |publisher=NASA }} and threatening the continuation of the mission.{{Cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=May 15, 2013 |title=Equipment Failure May Cut Kepler Mission Short |url=https://www.nytimes.com/2013/05/16/science/space/equipment-failure-may-cut-kepler-mission-short.html |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20130516013231/https://www.nytimes.com/2013/05/16/science/space/equipment-failure-may-cut-kepler-mission-short.html |archive-date=May 16, 2013 |access-date=May 15, 2013 |work=The New York Times }}

On August 15, 2013, NASA announced that they had given up trying to fix the two failed reaction wheels. This meant the current mission needed to be modified, but it did not necessarily mean the end of planet hunting. NASA had asked the space science community to propose alternative mission plans "potentially including an exoplanet search, using the remaining two good reaction wheels and thrusters".{{Cite press release |date=August 15, 2013 |title=NASA Ends Attempts to Fully Recover Kepler Spacecraft, Potential New Missions Considered |url=https://www.nasa.gov/news-release/nasa-ends-attempts-to-fully-recover-kepler-spacecraft-potential-new-missions-considered/ |url-status=live |archive-url=https://web.archive.org/web/20240312002252/https://www.nasa.gov/news-release/nasa-ends-attempts-to-fully-recover-kepler-spacecraft-potential-new-missions-considered/ |archive-date=March 12, 2024 |access-date=August 15, 2013 |publisher=NASA |id=13-254 }}{{Cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=August 15, 2013 |title=NASA's Kepler Mended, but May Never Fully Recover |url=https://www.nytimes.com/2013/08/16/science/space/nasas-kepler-mended-but-may-never-fully-recover.html |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20130816005723/http://www.nytimes.com/2013/08/16/science/space/nasas-kepler-mended-but-may-never-fully-recover.html |archive-date=August 16, 2013 |access-date=August 15, 2013 |work=The New York Times }}{{Cite news |last=Wall |first=Mike |date=August 15, 2013 |title=Planet-Hunting Days of NASA's Kepler Spacecraft Likely Over |url=https://www.space.com/22387-nasa-planet-hunting-kepler-spacecraft-problems.html |url-status=live |archive-url=https://web.archive.org/web/20240627221858/https://www.space.com/22387-nasa-planet-hunting-kepler-spacecraft-problems.html |archive-date=June 27, 2024 |access-date=August 15, 2013 |work=Space.com }}{{Cite news |date=August 16, 2013 |title=Kepler: NASA retires prolific telescope from planet-hunting duties |url=https://www.bbc.co.uk/news/science-environment-23724344 |url-status=live |archive-url=https://web.archive.org/web/20221226002235/https://www.bbc.com/news/science-environment-23724344 |archive-date=December 26, 2022 |work=BBC News }} On November 18, 2013, the K2 "Second Light" proposal was reported. This would include utilizing the disabled Kepler in a way that could detect habitable planets around smaller, dimmer red dwarfs.{{Cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=November 18, 2013 |title=New Plan for a Disabled Kepler |url=https://www.nytimes.com/2013/11/19/science/space/new-plan-for-a-disabled-kepler.html |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20131119142448/http://www.nytimes.com/2013/11/19/science/space/new-plan-for-a-disabled-kepler.html |archive-date=November 19, 2013 |access-date=November 18, 2013 |work=The New York Times |location=Mountain View, California }} On May 16, 2014, NASA announced the approval of the K2 extension.{{cite web |url=http://www.nasa.gov/content/ames/kepler-mission-manager-update-k2-has-been-approved/ |title=Kepler Mission Manager Update: K2 Has Been Approved! |date=May 16, 2014 |publisher=NASA |access-date=May 17, 2014 |others=NASA Official: Brian Dunbar; Image credit(s): NASA Ames/W. Stenzel |first=Charlie |last=Sobeck |editor1-first=Michele |editor1-last=Johnson |archive-url=https://web.archive.org/web/20140517191944/http://www.nasa.gov/content/ames/kepler-mission-manager-update-k2-has-been-approved/ |archive-date=May 17, 2014 |url-status=live }}

By January 2015, Kepler and its follow-up observations had found 1,013 confirmed exoplanets in about 440 star systems, along with a further 3,199 unconfirmed planet candidates.{{efn-ua|This does not include Kepler candidates without a KOI designation, such as circumbinary planets, or candidates found in the Planet Hunters project.}}{{Cite news |last=Wall |first=Mike |date=June 14, 2013 |title=Ailing NASA Telescope Spots 503 New Alien Planet Candidates |url=https://www.space.com/21570-nasa-kepler-alien-planet-candidates.html |url-status=live |archive-url=https://web.archive.org/web/20240617194323/https://www.space.com/21570-nasa-kepler-alien-planet-candidates.html |archive-date=June 17, 2024 |access-date=June 15, 2013 |work=Space.com |agency=TechMediaNetwork }}{{cite web |title=NASA's Exoplanet Archive KOI table |url=http://exoplanetarchive.ipac.caltech.edu/cgi-bin/ExoTables/nph-exotbls?dataset=cumulative |publisher=NASA |access-date=February 28, 2014 |archive-url=https://archive.today/20140226203336/http://exoplanetarchive.ipac.caltech.edu/cgi-bin/ExoTables/nph-exotbls?dataset=cumulative |archive-date=February 26, 2014 |url-status=dead }} Four planets have been confirmed through Kepler's K2 mission.{{cite journal |title=A nearby M star with three transiting super-Earths discovered by K2 |arxiv=1501.03798 |first1=Ian J. M. |last1=Crossfield |first2=Erik |last2=Petigura |first3=Joshua |last3=Schlieder |first4=Andrew W. |last4=Howard |first5=B. J. |last5=Fulton |first6=Kimberly M. |last6=Aller |first7=David R. |last7=Ciardi |first8=Sebastien |last8=Lepine |first9=Thomas |last9=Barclay |first10=Imke |last10=de Pater |first11=Katherine |last11=de Kleer |first12=Elisa V. |last12=Quintana |first13=Jessie L. |last13=Christiansen |first14=Eddie |last14=Schlafly |first15=Lisa |last15=Kaltenegger |first16=Justin R. |last16=Crepp |first17=Thomas |last17=Henning |first18=Christian |last18=Obermeier |first19=Niall |last19=Deacon |first20=Brad M. S. |last20=Hansen |first21=Michael C. |last21=Liu |first22=Tom |last22=Greene |first23=Steve B. |last23=Howell |first24=Travis |last24=Barman |first25=Christoph |last25=Mordasini |display-authors=5 |date=January 2015 |doi=10.1088/0004-637X/804/1/10 |volume=804 |issue=1 |journal=The Astrophysical Journal |page=10 |bibcode=2015ApJ...804...10C|s2cid=14204860 }} In November 2013, astronomers estimated, based on Kepler space mission data, that there could be as many as 40 billion rocky Earth-size exoplanets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way.{{Cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=November 4, 2013 |title=Far-Off Planets Like the Earth Dot the Galaxy |url=https://www.nytimes.com/2013/11/05/science/cosmic-census-finds-billions-of-planets-that-could-be-like-earth.html |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20150324173042/http://www.nytimes.com/2013/11/05/science/cosmic-census-finds-billions-of-planets-that-could-be-like-earth.html |archive-date=March 24, 2015 |access-date=November 5, 2013 |work=The New York Times }}{{cite journal |last1=Petigura |first1=Erik A. |last2=Howard |first2=Andrew W. |last3=Marcy |first3=Geoffrey W. |title=Prevalence of Earth-size planets orbiting Sun-like stars |date=October 31, 2013 |journal=Proceedings of the National Academy of Sciences of the United States |doi=10.1073/pnas.1319909110 |arxiv=1311.6806 |bibcode=2013PNAS..11019273P |volume=110 |issue=48 |pages=19273–19278 |pmid=24191033 |pmc=3845182|doi-access=free }}{{Cite news |date=January 7, 2013 |title=17 Billion Earth-Size Alien Planets Inhabit Milky Way |url=https://www.space.com/19157-billions-earth-size-alien-planets-aas221.html |url-status=live |archive-url=https://web.archive.org/web/20240920230538/https://www.space.com/19157-billions-earth-size-alien-planets-aas221.html |archive-date=September 20, 2024 |access-date=January 8, 2013 |work=Space.com }} It is estimated that 11 billion of these planets may be orbiting Sun-like stars.{{Cite news |last=Khan |first=Amina |date=November 4, 2013 |title=Milky Way may host billions of Earth-size planets |url=https://www.latimes.com/science/la-sci-earth-like-planets-20131105-story.html |url-status=live |archive-url=https://web.archive.org/web/20240525123929/https://www.latimes.com/science/la-sci-earth-like-planets-20131105-story.html |archive-date=May 25, 2024 |access-date=November 5, 2013 |work=Los Angeles Times }} The nearest such planet may be {{convert|12|ly|pc|order=flip|lk=on}} away, according to the scientists.

On January 6, 2015, NASA announced the 1,000th confirmed exoplanet discovered by the Kepler space telescope. Four of the newly confirmed exoplanets were found to orbit within habitable zones of their related stars: three of the four, Kepler-438b, Kepler-442b and Kepler-452b, are almost Earth-size and likely rocky; the fourth, Kepler-440b, is a super-Earth.{{Cite press release |last1=Clavin |first1=Whitney |last2=Chou |first2=Felicia |last3=Johnson |first3=Michele |date=January 6, 2015 |title=NASA's Kepler Marks 1,000th Exoplanet Discovery, Uncovers More Small Worlds in Habitable Zones |url=https://www.jpl.nasa.gov/news/nasas-kepler-marks-1000th-exoplanet-discovery-uncovers-more-small-worlds-in-habitable-zones/ |url-status=live |archive-url=https://web.archive.org/web/20240927125427/https://www.jpl.nasa.gov/news/nasas-kepler-marks-1000th-exoplanet-discovery-uncovers-more-small-worlds-in-habitable-zones/ |archive-date=September 27, 2024 |access-date=January 6, 2015 |publisher=NASA / JPL |id=2015-003 }} On May 10, 2016, NASA verified 1,284 new exoplanets found by Kepler, the single largest finding of planets to date.{{Cite press release |date=May 10, 2016 |title=NASA's Kepler Mission Announces Largest Collection of Planets Ever Discovered |url=https://www.nasa.gov/news-release/nasas-kepler-mission-announces-largest-collection-of-planets-ever-discovered/ |url-status=live |archive-url=https://web.archive.org/web/20241003222626/https://www.nasa.gov/news-release/nasas-kepler-mission-announces-largest-collection-of-planets-ever-discovered/ |archive-date=October 3, 2024 |access-date=May 10, 2016 |publisher=NASA |id=16-051 }}{{cite web |url=http://www.nasa.gov/feature/ames/kepler/briefingmaterials160510 |title=Briefing materials: 1,284 Newly Validated Kepler Planets |publisher=NASA |date=May 10, 2016 |access-date=May 10, 2016 |archive-date=May 5, 2019 |archive-url=https://web.archive.org/web/20190505193145/https://www.nasa.gov/feature/ames/kepler/briefingmaterials160510/ |url-status=dead }}{{Cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=May 10, 2016 |title=Kepler Finds 1,284 New Planets |url=https://www.nytimes.com/2016/05/11/science/kepler-planets-nasa.html |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20160510204552/http://www.nytimes.com/2016/05/11/science/kepler-planets-nasa.html |archive-date=May 10, 2016 |access-date=May 11, 2016 |work=The New York Times }}

Kepler data have also helped scientists observe and understand supernovae; measurements were collected every half-hour so the light curves were especially useful for studying these types of astronomical events.{{cite journal |title=Kepler clue to supernova puzzle |journal=Nature |date=January 16, 2014 |publisher=Nature Publishing Group |issn=1476-4687 |oclc=01586310 |doi=10.1038/505274a |pmid=24429610 |pages=274–275 |volume=505 |issue=7483 |first=Ron |last=Cowen |bibcode=2014Natur.505..274C |doi-access=free }}

On October 30, 2018, after the spacecraft ran out of fuel, NASA announced that the telescope would be retired.{{Cite press release |date=October 30, 2018 |title=NASA Retires Kepler Space Telescope, Passes Planet-Hunting Torch |url=https://www.nasa.gov/news-release/nasa-retires-kepler-space-telescope-passes-planet-hunting-torch/ |url-status=live |archive-url=https://web.archive.org/web/20241003081649/https://www.nasa.gov/news-release/nasa-retires-kepler-space-telescope-passes-planet-hunting-torch/ |archive-date=October 3, 2024 |publisher=NASA |id=18-092 }} The telescope was shut down the same day, bringing an end to its nine-year service. Kepler observed 530,506 stars and discovered 2,662 exoplanets over its lifetime.{{Cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=October 30, 2018 |title=Kepler, the Little NASA Spacecraft That Could, No Longer Can |url=https://www.nytimes.com/2018/10/30/science/nasa-kepler-exoplanet.html |url-status=live |archive-url=https://web.archive.org/web/20181030211627/https://www.nytimes.com/2018/10/30/science/nasa-kepler-exoplanet.html |archive-date=October 30, 2018 |access-date=October 31, 2018 |newspaper=The New York Times }} A newer NASA mission, TESS, launched in 2018, is continuing the search for exoplanets.{{cite news |last1=Wiessinger |first1=Scott |last2=Lepsch |first2=Aaron E. |last3=Kazmierczak |first3=Jeanette |last4=Reddy |first4=Francis |last5=Boyd |first5=Padi |title=NASA's TESS Releases First Science Image |url=https://svs.gsfc.nasa.gov/13069 |date=September 17, 2018 |work=NASA |access-date=October 31, 2018 }}

File:Kepler in Astrotech's Hazardous Processing Facility (KSC-2009-1645).jpg

File:Kepler Space Telescope.stl

The telescope has a mass of {{convert|1039|kg|lb}} and contains a Schmidt camera with a {{convert|0.95|m|in|1|adj=on|sp=us}} front corrector plate (lens) feeding a {{convert|1.4|m|in|0|adj=on|sp=us}} primary mirror—at the time of its launch this was the largest mirror on any telescope outside Earth orbit,{{cite web |last=Atkins |first=William |title=Exoplanet Search Begins with French Launch of Corot Telescope Satellite |url=http://www.itwire.com/content/view/8299/1066/ |publisher=iTWire |date=December 28, 2008 |access-date=May 6, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20081204114533/http://www.itwire.com/content/view/8299/1066/ |archive-date=December 4, 2008 }} though the Herschel Space Observatory took this title a few months later. Its telescope has a 115 deg² (about 12-degree diameter) field of view (FoV), roughly equivalent to the size of one's fist held at arm's length. Of this, 105 deg² is of science quality, with less than 11% vignetting. The photometer has a soft focus to provide excellent photometry, rather than sharp images. The mission goal was a combined differential photometric precision (CDPP) of 20 ppm for a m(V)=12 Sun-like star for a 6.5-hour integration, though the observations fell short of this objective (see mission status).

File:Keplerspacecraft-FocalPlane-cutout.svg.]]

The focal plane of the spacecraft's camera is made out of forty-two {{convert|50|xx|25|mm|in|0|abbr=on}} CCDs at 2200×1024 pixels each, possessing a total resolution of 94.6 megapixels,{{cite web |url=http://www.nasa.gov/mission_pages/kepler/spacecraft/index.html |title=Kepler: Spacecraft and Instrument |publisher=NASA |editor-first=Michele |editor-last=Johnson |date=July 30, 2015 |access-date=December 11, 2016}} which at the time made it the largest camera system launched into space. The array was cooled by heat pipes connected to an external radiator. The CCDs were read out every 6.5 seconds (to limit saturation) and co-added on board for 58.89 seconds for short cadence targets, and 1765.5 seconds (29.4 minutes) for long cadence targets.{{cite web |url=https://keplerscience.arc.nasa.gov/data-products.html |archive-url=https://web.archive.org/web/20160107031435/http://keplerscience.arc.nasa.gov/data-products.html |url-status=dead |archive-date=January 7, 2016 |title=Kepler and K2 data products |publisher=NASA |editor-first=Geert |editor-last=Barentsen |date=August 16, 2017 |access-date=August 24, 2017}} Due to the larger bandwidth requirements for the former, these were limited in number to 512 compared to 170,000 for long cadence. However, even though at launch Kepler had the highest data rate of any NASA mission,{{Citation needed|date=October 2015}} the 29-minute sums of all 95 million pixels constituted more data than could be stored and sent back to Earth. Therefore, the science team pre-selected the relevant pixels associated with each star of interest, amounting to about 6 percent of the pixels (5.4 megapixels). The data from these pixels was then requantized, compressed and stored, along with other auxiliary data, in the on-board 16 gigabyte solid-state recorder. Data that was stored and downlinked includes science stars, p-mode stars, smear, black level, background and full field-of-view images.{{cite web |title=PyKE Primer – 2. Data Resources |url=http://keplergo.arc.nasa.gov/PyKEprimerResources.shtml |archive-url=https://web.archive.org/web/20130217132822/http://keplergo.arc.nasa.gov/PyKEprimerResources.shtml |url-status=dead |archive-date=February 17, 2013 |publisher=NASA |access-date=March 12, 2014}}

File:comparison optical telescope primary mirrors.svg

The Kepler primary mirror is {{convert|1.4|m|ft|sp=us}} in diameter. Manufactured by glass maker Corning using ultra-low expansion (ULE) glass, the mirror is specifically designed to have a mass only 14% that of a solid mirror of the same size.{{cite web |title=Kepler Primary Mirror |url=http://www.nasa.gov/mission_pages/kepler/multimedia/images/PMA_backside_inspection_1_at_SOC.html |publisher=NASA |access-date=April 5, 2013 |archive-date=June 18, 2020 |archive-url=https://web.archive.org/web/20200618084431/https://www.nasa.gov/mission_pages/kepler/multimedia/images/PMA_backside_inspection_1_at_SOC.html |url-status=dead }}{{cite web |title=Corning To Build Primary Mirror For Kepler Photometer |url=http://www.spacedaily.com/news/extrasolar-03q.html |access-date=April 5, 2013}} To produce a space telescope system with sufficient sensitivity to detect relatively small planets, as they pass in front of stars, a very high reflectance coating on the primary mirror was required. Using ion assisted evaporation, Surface Optics Corp. applied a protective nine-layer silver coating to enhance reflection and a dielectric interference coating to minimize the formation of color centers and atmospheric moisture absorption.{{cite journal |last1=Fulton L. |first1=Michael |last2=Dummer |first2=Richard S. |date=2011 |title=Advanced Large Area Deposition Technology for Astronomical and Space Applications |journal=Vacuum & Coating Technology |issue=December 2011 |pages=43–47 |url=http://e-ditionsbyfry.com/Olive/ODE/VTC/Default.aspx?href=VTC/2011/12/01 |access-date=April 6, 2013 |archive-url=https://web.archive.org/web/20130512233653/http://e-ditionsbyfry.com/Olive/ODE/VTC/Default.aspx?href=VTC%2F2011%2F12%2F01 |archive-date=May 12, 2013 |url-status=dead |df=mdy-all }}{{cite press release |title=Ball Aerospace Completes Primary Mirror and Detector Array Assembly Milestones for Kepler Mission |url=http://www.spaceref.com/news/viewpr.html?pid=23610 |archive-url=https://archive.today/20130616050826/http://www.spaceref.com/news/viewpr.html?pid=23610 |url-status=dead |archive-date=June 16, 2013 |date=September 25, 2007 |publisher=Ball Aerospace and Technologies |work=SpaceRef.com |access-date=April 6, 2013 }}

In terms of photometric performance, Kepler worked well, much better than any Earth-bound telescope, but short of design goals. The objective was a combined differential photometric precision (CDPP) of 20 parts per million (PPM) on a magnitude 12 star for a 6.5-hour integration. This estimate was developed allowing 10 ppm for stellar variability, roughly the value for the Sun. The obtained accuracy for this observation has a wide range, depending on the star and position on the focal plane, with a median of 29 ppm. Most of the additional noise appears to be due to a larger-than-expected variability in the stars themselves (19.5 ppm as opposed to the assumed 10.0 ppm), with the rest due to instrumental noise sources slightly larger than predicted.{{cite journal |last1=Gilliland |first1=Ronald L. |date=2011 |title=Kepler Mission Stellar and Instrument Noise Properties |arxiv=1107.5207 |display-authors=etal |doi=10.1088/0067-0049/197/1/6 |volume=197 |issue=1 |journal=The Astrophysical Journal Supplement Series |page=6 |bibcode=2011ApJS..197....6G|s2cid=118626534 }}{{Cite conference |editor1-last=Oschmann |editor1-first=Jacobus M. Jr. |editor2-last=Clampin |editor2-first=Mark C. |editor3-last=MacEwen |editor3-first=Howard A. |last1=Caldwell |first1=Douglas A. |last2=van Cleve |first2=Jeffrey E. |last3=Jenkins |first3=Jon M. |last4=Argabright |first4=Vic S. |last5=Kolodziejczak |first5=Jeffery J. |last6=Dunham |first6=Edward W. |last7=Geary |first7=John C. |last8=Tenenbaum |first8=Peter |last9=Chandrasekaran |first9=Hema |last10=Li |first10=Jie |last11=Wu |first11=Hayley |last12=von Wilpert |first12=Jason |date=July 2010 |title=Kepler instrument performance: An in-flight update |url=http://kepler.nasa.gov/Science/ForScientists/papersAndDocumentation/SOCpapers/spie_2010_instrument_char_web_version.pdf |conference=Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave |location=San Diego, California, United States |publisher=SPIE |volume=7731 |at=773117 |bibcode=2010SPIE.7731E..17C |doi=10.1117/12.856638 |archive-url=https://web.archive.org/web/20110721122315/http://kepler.nasa.gov/Science/ForScientists/papersAndDocumentation/SOCpapers/spie_2010_instrument_char_web_version.pdf |archive-date=July 21, 2011 |conference-url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7731.toc |s2cid=121398671 |url-status=dead |display-authors=5 }}

Because decrease in brightness from an Earth-size planet transiting a Sun-like star is so small, only 80 ppm, the increased noise means each individual transit is only a 2.7 σ event, instead of the intended 4 σ. This, in turn, means more transits must be observed to be sure of a detection. Scientific estimates indicated that a mission lasting 7 to 8 years, as opposed to the originally planned 3.5 years, would be needed to find all transiting Earth-sized planets.{{cite web |url=http://www.skyandtelescope.com/news/126242378.html |title=Kepler's Dilemma: Not Enough Time |publisher=Sky and Telescope |first=Kelly |last=Beatty |date=September 2011 |access-date=August 2, 2011 |archive-date=October 22, 2013 |archive-url=https://web.archive.org/web/20131022190523/http://www.skyandtelescope.com/news/126242378.html |url-status=dead }} On April 4, 2012, the Kepler mission was approved for extension through the fiscal year 2016,{{cite web |url=http://kepler.nasa.gov/news/index.cfm?FuseAction=ShowNews&NewsID=199 |archive-url=https://web.archive.org/web/20120707131538/http://kepler.nasa.gov/news/index.cfm?FuseAction=ShowNews&NewsID=199 |url-status=dead |archive-date=July 7, 2012 |title=NASA Approves Kepler Mission Extension |publisher=NASA |date=April 4, 2012}} but this also depended on all remaining reaction wheels staying healthy, which turned out not to be the case (see Reaction wheel issues below).

Image:LombergA1024.jpg

File:Kepler-earthdirection 2009-2019.png

Kepler orbits the Sun,{{cite web |last1=Koch |first1=David |last2=Gould |first2=Alan |title=Kepler Mission: Launch Vehicle and Orbit |url=http://kepler.nasa.gov/sci/design/orbit.html |archive-url=https://web.archive.org/web/20070622161529/http://kepler.nasa.gov/sci/design/orbit.html |archive-date=June 22, 2007 |publisher=NASA |date=March 2009 |url-status=dead |access-date=March 14, 2009}} which avoids Earth occultations, stray light, and gravitational perturbations and torques inherent in an Earth orbit.

NASA has characterized Kepler's orbit as "Earth-trailing".{{cite web |url=http://www.nasa.gov/mission_pages/kepler/spacecraft/index-mission.html |title=Kepler: Spacecraft and Instrument |publisher=NASA |access-date=December 21, 2011 |archive-date=October 6, 2020 |archive-url=https://web.archive.org/web/20201006083211/https://www.nasa.gov/mission_pages/kepler/spacecraft/index-mission.html |url-status=dead }} With an orbital period of 372.5 days, Kepler is slowly falling farther behind Earth (about 16 million miles per annum). {{As of|2018|05|01|df=US}}, the distance to Kepler from Earth was about {{convert|0.917|AU|e6km|0|abbr=unit}}. This means that after about 26 years Kepler will reach the other side of the Sun and will get back to the neighborhood of the Earth after 51 years.

Until 2013 the photometer pointed to a field in the northern constellations of Cygnus, Lyra and Draco, which is well out of the ecliptic plane, so that sunlight never enters the photometer as the spacecraft orbits. This is also the direction of the Solar System's motion around the center of the galaxy. Thus, the stars which Kepler observed are roughly the same distance from the Galactic Center as the Solar System, and also close to the galactic plane. This fact is important if position in the galaxy is related to habitability, as suggested by the Rare Earth hypothesis.

Orientation is three-axis stabilized by sensing rotations using fine-guidance sensors located on the instrument focal plane (instead of rate sensing gyroscopes, e.g. as used on Hubble). and using reaction wheels and hydrazine thrusters{{Cite web|url=https://astrobiology.nasa.gov/news/the-kepler-space-telescope-mission-is-ending-but-its-legacy-will-keep-growing/|title = NASA Astrobiology}} to control the orientation.

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Image:Kepler orbit.pngs and equinoxes.]]

Kepler was operated out of Boulder, Colorado, by the Laboratory for Atmospheric and Space Physics (LASP) under contract to Ball Aerospace & Technologies. The spacecraft's solar array was rotated to face the Sun at the solstices and equinoxes, so as to optimize the amount of sunlight falling on the solar array and to keep the heat radiator pointing towards deep space. Together, LASP and Ball Aerospace controlled the spacecraft from a mission operations center located on the research campus of the University of Colorado. LASP performs essential mission planning and the initial collection and distribution of the science data. The mission's initial life-cycle cost was estimated at US$600 million, including funding for 3.5 years of operation. In 2012, NASA announced that the Kepler mission would be funded until 2016 at a cost of about $20 million per year.

NASA contacted the spacecraft using the X band communication link twice a week for command and status updates. Scientific data are downloaded once a month using the K_a band link at a maximum data transfer rate of approximately 550 kB/s. The high gain antenna is not steerable so data collection is interrupted for a day to reorient the whole spacecraft and the high gain antenna for communications to Earth.{{rp|16}} Kepler was the first mission to rely on K_a-band data downlink, and in turn collected statistics on K_a-band performance for later missions using this technology.{{cite web |url=https://personales.upv.es/thinkmind/dl/conferences/spacomm/spacomm_2016/spacomm_2016_2_30_20032.pdf |title=Performance Analysis of Operational Ka-band Link with Kepler}}

The Kepler space telescope conducted its own partial analysis on board and only transmitted scientific data deemed necessary to the mission in order to conserve bandwidth.{{cite news |last=Ng |first=Jansen |url=http://www.dailytech.com/Kepler+Mission+Sets+Out+to+Find+Planets+Using+CCD+Cameras/article14421.htm |title=Kepler Mission Sets Out to Find Planets Using CCD Cameras |work=DailyTech |date=March 8, 2009 |access-date=March 14, 2009 |archive-url=https://web.archive.org/web/20090310010146/http://www.dailytech.com/Kepler+Mission+Sets+Out+to+Find+Planets+Using+CCD+Cameras/article14421.htm |archive-date=March 10, 2009 |url-status=dead }}

Science data telemetry collected during mission operations at LASP is sent for processing to the Kepler Data Management Center (DMC) which is located at the Space Telescope Science Institute on the campus of Johns Hopkins University in Baltimore, Maryland. The science data telemetry is decoded and processed into uncalibrated FITS-format science data products by the DMC, which are then passed along to the Science Operations Center (SOC) at NASA Ames Research Center, for calibration and final processing. The SOC at NASA Ames Research Center (ARC) develops and operates the tools needed to process scientific data for use by the Kepler Science Office (SO). Accordingly, the SOC develops the pipeline data processing software based on scientific algorithms developed jointly by the SO and SOC. During operations, the SOC:{{cite web |url=http://archive.stsci.edu/kepler/manuals/KSCI-19081-002-KDPH.pdf |title=Kepler Data Processing Handbook (KSCI-19081-002) |date=January 25, 2017 |first=Jon M. |last=Jenkins |publisher=NASA}}

1. Receives uncalibrated pixel data from the DMC
2. Applies the analysis algorithms to produce calibrated pixels and light curves for each star
3. Performs transit searches for detection of planets (threshold-crossing events, or TCEs)
4. Performs data validation of candidate planets by evaluating various data products for consistency as a way to eliminate false positive detections

The SOC also evaluates the photometric performance on an ongoing basis and provides the performance metrics to the SO and Mission Management Office. Finally, the SOC develops and maintains the project's scientific databases, including catalogs and processed data. The SOC finally returns calibrated data products and scientific results back to the DMC for long-term archiving, and distribution to astronomers around the world through the Multimission Archive at STScI (MAST).

On July 14, 2012, one of the four reaction wheels used for fine pointing of the spacecraft failed.{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20122407.html |title=Kepler Mission Manager Update |date=July 24, 2012 |first=Roger |last=Hunter |publisher=NASA |access-date=July 27, 2012 |archive-date=January 6, 2021 |archive-url=https://web.archive.org/web/20210106030017/https://www.nasa.gov/mission_pages/kepler/news/keplerm-20122407.html |url-status=dead }} While Kepler requires only three reaction wheels to accurately aim the telescope, another failure would leave the spacecraft unable to aim at its original field.{{Cite magazine |last=McKee |first=Maggie |date=July 24, 2012 |title=Kepler glitch may lower odds of finding Earth's twin |url=https://www.newscientist.com/article/dn22096-kepler-glitch-may-lower-odds-of-finding-earths-twin/ |url-status=live |archive-url=https://web.archive.org/web/20240702172027/https://www.newscientist.com/article/dn22096-kepler-glitch-may-lower-odds-of-finding-earths-twin/ |archive-date=July 2, 2024 |magazine=New Scientist }}

After showing some problems in January 2013, a second reaction wheel failed on May 11, 2013, ending Kepler's primary mission. The spacecraft was put into safe mode, then from June to August 2013 a series of engineering tests were done to try to recover either failed wheel. By August 15, 2013, it was decided that the wheels were unrecoverable, and an engineering report was ordered to assess the spacecraft's remaining capabilities.

This effort ultimately led to the "K2" follow-on mission observing different fields near the ecliptic.

The reaction wheel failures were traced back to pitting caused by arcing between the steel ball bearings in the reaction wheel. The arcing was in turn caused by coronal mass ejections (CMEs) from the sun. Kepler's position far from Earth helped in determining the cause, due to the significant delay between the arrival of a CME at Kepler and Earth.{{cite web |url=https://esmats.eu/esmatspapers/pastpapers/pdfs/2017/bialke.pdf |title=A Newly Discovered Branch of the Fault Tree Explaining Systematic Reaction Wheel Failures and Anomalies}}

Image:Ignition of Kepler's Delta II 7925-10L.jpg

Image:Keplerspacecraft-20110215.jpg

Image:Keplerpacecraft.019e.jpg

In January 2006, the project's launch was delayed eight months because of budget cuts and consolidation at NASA.{{cite web |last=Borucki |first=W. J. |date=May 22, 2010 |url=http://kepler.nasa.gov/Mission/QuickGuide/history/ |title=Brief History of the Kepler Mission |publisher=NASA |access-date=April 23, 2011 |archive-url=https://web.archive.org/web/20110721123028/http://kepler.nasa.gov/Mission/QuickGuide/history/ |archive-date=July 21, 2011 |url-status=dead }} It was delayed again by four months in March 2006 due to fiscal problems. At this time, the high-gain antenna was changed from a gimballed design to one fixed to the frame of the spacecraft to reduce cost and complexity, at the cost of one observation day per month.

The Kepler observatory was launched on March 7, 2009, at 03:49:57 UTC aboard a Delta II rocket from Cape Canaveral Air Force Station, Florida.{{cite web |title=KASC Scientific Webpage |url=http://astro.phys.au.dk/KASC/ |work=Kepler Asteroseismic Science Consortium |publisher=Aarhus University |date=March 14, 2009 |access-date=March 14, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20120505003051/http://astro.phys.au.dk/KASC/ |archive-date=May 5, 2012 }} The launch was a success and all three stages were completed by 04:55 UTC. The cover of the telescope was jettisoned on April 7, 2009, and the first light images were taken on the next day.{{Cite news |last=DeVore |first=Edna |date=April 9, 2009 |title=Planet-Hunting Kepler Telescope Lifts Its Lid |url=https://www.space.com/6562-planet-hunting-kepler-telescope-lifts-lid.html |url-status=live |archive-url=https://web.archive.org/web/20240629195755/https://www.space.com/6562-planet-hunting-kepler-telescope-lifts-lid.html |archive-date=June 29, 2024 |access-date=April 14, 2009 |work=Space.com }}{{cite web |url=http://www.nasa.gov/home/hqnews/2009/apr/HQ_09-085_Kepler_First_Light.html |title=NASA's Kepler Captures First Views of Planet-Hunting Territory |date=April 16, 2009 |publisher=NASA |access-date=April 16, 2009 |archive-date=April 18, 2009 |archive-url=https://web.archive.org/web/20090418045111/http://www.nasa.gov/home/hqnews/2009/apr/HQ_09-085_Kepler_First_Light.html |url-status=dead }}

On April 20, 2009, it was announced that the Kepler science team had concluded that further refinement of the focus would dramatically increase the scientific return.{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20090420.html |title=04.20.09 – Kepler Mission Manager Update |date=April 20, 2009 |publisher=NASA |access-date=April 20, 2009 |archive-date=March 3, 2016 |archive-url=https://web.archive.org/web/20160303224127/http://www.nasa.gov/mission_pages/kepler/news/keplerm-20090420.html |url-status=dead }} On April 23, 2009, it was announced that the focus had been successfully optimized by moving the primary mirror 40 micrometers (1.6 thousandths of an inch) towards the focal plane and tilting the primary mirror 0.0072 degree.{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20090424.html |title=04.23.09 – Kepler Mission Manager Update |date=April 23, 2009 |publisher=NASA |access-date=April 27, 2009 |archive-date=July 22, 2016 |archive-url=https://web.archive.org/web/20160722060640/http://www.nasa.gov/mission_pages/kepler/news/keplerm-20090424.html |url-status=dead }}

On May 13, 2009, at 00:01 UTC, Kepler successfully completed its commissioning phase and began its search for planets around other stars.{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20090514.html |title=05.14.09 – Kepler Mission Manager Update |date=May 14, 2009 |publisher=NASA |access-date=May 16, 2009 |archive-date=August 4, 2020 |archive-url=https://web.archive.org/web/20200804094311/https://www.nasa.gov/mission_pages/kepler/news/keplerm-20090514.html |url-status=dead }}{{cite web |title=Let the Planet Hunt Begin |url=http://www.nasa.gov/mission_pages/kepler/news/kepler-200905013.html |publisher=NASA |date=May 13, 2009 |access-date=May 13, 2009 |archive-date=July 28, 2020 |archive-url=https://web.archive.org/web/20200728065005/https://www.nasa.gov/mission_pages/kepler/news/kepler-200905013.html |url-status=dead }}

On June 19, 2009, the spacecraft successfully sent its first science data to Earth. It was discovered that Kepler had entered safe mode on June 15. A second safe mode event occurred on July 2. In both cases the event was triggered by a processor reset. The spacecraft resumed normal operation on July 3 and the science data that had been collected since June 19 was downlinked that day.{{cite web |url=http://kepler.nasa.gov/Mission/mmupdates/missionManagerArchive/ |archive-url=https://web.archive.org/web/20100528141716/http://kepler.nasa.gov/Mission/mmupdates/missionManagerArchive/ |url-status=dead |archive-date=May 28, 2010 |title=2009 July 7 Mission Manager Update |date=July 7, 2009 |publisher=NASA |access-date=April 23, 2011}} On October 14, 2009, the cause of these safing events was determined to be a low voltage power supply that provides power to the RAD750 processor.{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20091014.html |title=Kepler Mission Manager Update |date=October 14, 2009 |publisher=NASA |access-date=October 18, 2009 |archive-date=May 10, 2020 |archive-url=https://web.archive.org/web/20200510043155/https://www.nasa.gov/mission_pages/kepler/news/keplerm-20091014.html |url-status=dead }} On January 12, 2010, one portion of the focal plane transmitted anomalous data, suggesting a problem with focal plane MOD-3 module, covering two out of Kepler's 42 CCDs. {{As of|2010|10}}, the module was described as "failed", but the coverage still exceeded the science goals.{{cite web |title=Kepler outlook positive; Followup Observing Program in full swing |url=http://kepler.nasa.gov/news/mmu/index.cfm?FuseAction=ShowNews&NewsID=55 |archive-url=https://web.archive.org/web/20110721122210/http://kepler.nasa.gov/news/mmu/index.cfm?FuseAction=ShowNews&NewsID=55 |url-status=dead |archive-date=July 21, 2011 |date=August 23, 2010 |access-date=April 23, 2011}}

Kepler downlinked roughly twelve gigabytes of data{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20090923.html |title=Kepler Mission Manager Update |date=September 23, 2009 |publisher=NASA |access-date=September 25, 2009 |archive-date=April 17, 2020 |archive-url=https://web.archive.org/web/20200417112011/https://www.nasa.gov/mission_pages/kepler/news/keplerm-20090923.html |url-status=dead }} about once per month.{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20091105.html |title=Kepler Mission Manager Update |date=November 5, 2009 |publisher=NASA |access-date=November 8, 2009 |archive-date=July 23, 2020 |archive-url=https://web.archive.org/web/20200723081644/https://www.nasa.gov/mission_pages/kepler/news/keplerm-20091105.html |url-status=dead }}

File:Kepler FOV hiRes.jpg]]

Kepler has a fixed field of view (FOV) against the sky. The diagram to the right shows the celestial coordinates and where the detector fields are located, along with the locations of a few bright stars with celestial north at the top left corner. The mission website has a calculator[https://web.archive.org/web/20040725111550/http://www.kepler.nasa.gov/cgi-bin/ra2pix.pl mission website calculator] that will determine if a given object falls in the FOV, and if so, where it will appear in the photo detector output data stream. Data on exoplanet candidates is submitted to the Kepler Follow-up Program, or KFOP, to conduct follow-up observations.

File:MilkywaykeplerfovbyCRoberts.jpg, Lyra and Draco]]

Kepler's field of view covers 115 square degrees, around 0.25 percent of the sky, or "about two scoops of the Big Dipper". Thus, it would require around 400 Kepler-like telescopes to cover the whole sky.{{cite web |url=http://www.ballaerospace.com/page.jsp?page=186 |title=Kepler mission & program information |publisher=Ball Aerospace & Technologies |access-date=September 18, 2012}} The Kepler field contains portions of the constellations Cygnus, Lyra, and Draco.

The nearest star system in Kepler's field of view is the triple star system Gliese 1245, 15 light years from the Sun. The brown dwarf WISE J2000+3629, 22.8 ± 1 light years from the Sun is also in the field of view, but is invisible to Kepler due to emitting light primarily in infrared wavelengths.

The scientific objective of the Kepler space telescope was to explore the structure and diversity of planetary systems.{{cite web |last1=Koch |first1=David |last2=Gould |first2=Alan |title=Overview of the Kepler Mission |url=http://www.cfa.harvard.edu/kepler/papers/2004/SPIE.Glasgow.Koch.pdf |publisher=SPIE |date=2004 |access-date=December 9, 2010}} This spacecraft observes a large sample of stars to achieve several key goals:

• To determine how many Earth-size and larger planets there are in or near the habitable zone (often called "Goldilocks planets"){{Cite magazine |last=Muir |first=Hazel |date=April 25, 2007 |title='Goldilocks' planet may be just right for life |url=https://www.newscientist.com/article/dn11710-goldilocks-planet-may-be-just-right-for-life/ |url-status=live |archive-url=https://web.archive.org/web/20240704181139/https://www.newscientist.com/article/dn11710-goldilocks-planet-may-be-just-right-for-life/ |archive-date=July 4, 2024 |access-date=April 2, 2009 |magazine=New Scientist }} of a wide variety of spectral types of stars.
• To determine the range of size and shape of the orbits of these planets.
• To estimate how many planets there are in multiple-star systems.
• To determine the range of orbit size, brightness, size, mass and density of short-period giant planets.
• To identify additional members of each discovered planetary system using other techniques.
• Determine the properties of those stars that harbor planetary systems.

Most of the exoplanets previously detected by other projects were giant planets, mostly the size of Jupiter and bigger. Kepler was designed to look for planets 30 to 600 times less massive, closer to the order of Earth's mass (Jupiter is 318 times more massive than Earth). The method used, the transit method, involves observing repeated transit of planets in front of their stars, which causes a slight reduction in the star's apparent magnitude, on the order of 0.01% for an Earth-size planet. The degree of this reduction in brightness can be used to deduce the diameter of the planet, and the interval between transits can be used to deduce the planet's orbital period, from which estimates of its orbital semi-major axis (using Kepler's laws) and its temperature (using models of stellar radiation) can be calculated.{{citation needed|date=March 2022}}

The probability of a random planetary orbit being along the line-of-sight to a star is the diameter of the star divided by the diameter of the orbit.{{cite web |author=David Koch and Alan Gould, curators |date=March 2009 |title=Kepler Mission: Characteristics of Transits (section 'Geometric Probability') |url=http://kepler.nasa.gov/sci/basis/character.html |publisher=NASA |access-date=September 21, 2009 |archive-url=https://web.archive.org/web/20090825002919/http://kepler.nasa.gov/sci/basis/character.html |archive-date=August 25, 2009 |url-status=dead}} For an Earth-size planet at 1 AU transiting a Sun-like star the probability is 0.47%, or about 1 in 210. For a planet like Venus orbiting a Sun-like star the probability is slightly higher, at 0.65%; If the host star has multiple planets, the probability of additional detections is higher than the probability of initial detection assuming planets in a given system tend to orbit in similar planes—an assumption consistent with current models of planetary system formation. For instance, if a Kepler-like mission conducted by aliens observed Earth transiting the Sun, there is a 7% chance that it would also see Venus transiting.

Kepler's 115 deg² field of view gives it a much higher probability of detecting Earth-sized planets than the Hubble Space Telescope, which has a field of view of only 10 sq. arc-minutes. Moreover, Kepler is dedicated to detecting planetary transits, while the Hubble Space Telescope is used to address a wide range of scientific questions, and rarely looks continuously at just one starfield. Of the approximately half-million stars in Kepler's field of view, around 150,000 stars were selected for observation. More than 90,000 are G-type stars on, or near, the main sequence. Thus, Kepler was designed to be sensitive to wavelengths of 400–865 nm where brightness of those stars peaks. Most of the stars observed by Kepler have apparent visual magnitude between 14 and 16 but the brightest observed stars have apparent visual magnitude of 8 or lower. Most of the planet candidates were initially not expected to be confirmed due to being too faint for follow-up observations.{{cite journal |title=Selection, Prioritization, and Characteristics of Kepler Target Stars |arxiv=1001.0349 |first1=N. M. |last1=Batalha |first2=W. J. |last2=Borucki |first3=D. G. |last3=Koch |first4=S. T. |last4=Bryson |first5=M. R. |last5=Haas |first6=T. M. |last6=Brown |first7=D. A. |last7=Caldwell |first8=R. L. |last8=Gilliland |first9=D. W. |last9=Latham |first10=S. |last10=Meibom |first11=D. G. |last11=Monet |display-authors=5 |date=January 3, 2010 |doi=10.1088/2041-8205/713/2/L109 |volume=713 |issue=2 |journal=The Astrophysical Journal |pages=L109–L114 |bibcode=2010ApJ...713L.109B|s2cid=39251116 }} All the selected stars are observed simultaneously, with the spacecraft measuring variations in their brightness every thirty minutes. This provides a better chance for seeing a transit. The mission was designed to maximize the probability of detecting planets orbiting other stars.{{cite web |title=Kepler Mission: Frequently Asked Questions |url=http://kepler.nasa.gov/about/faq.html |archive-url=https://web.archive.org/web/20070820000813/http://kepler.nasa.gov/about/faq.html |archive-date=August 20, 2007 |publisher=NASA |date=March 2009 |url-status=dead |access-date=March 14, 2009}}

Because Kepler must observe at least three transits to confirm that the dimming of a star was caused by a transiting planet, and because larger planets give a signal that is easier to check, scientists expected the first reported results to be larger Jupiter-size planets in tight orbits. The first of these were reported after only a few months of operation. Smaller planets, and planets farther from their sun would take longer, and discovering planets comparable to Earth were expected to take three years or longer.{{cite press release |title=Kepler Mission Rockets to Space in Search of Other Earth |url=https://science.nasa.gov/headlines/y2009/06mar_keplerlaunch.htm?friend |publisher=NASA |date=March 6, 2009 |access-date=March 14, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090315053534/http://science.nasa.gov/headlines/y2009/06mar_keplerlaunch.htm?friend |archive-date=March 15, 2009 }}

Data collected by Kepler is also being used for studying variable stars of various types and performing asteroseismology,{{cite journal |last1=Grigahcène |first1=A. |date=2010 |title=Hybrid γ Doradus – δ Scuti pulsators: New insights into the physics of the oscillations from Kepler observations |arxiv=1001.0747 |display-authors=etal |doi=10.1088/2041-8205/713/2/L192 |volume=713 |issue=2 |journal=The Astrophysical Journal |pages=L192–L197 |bibcode=2010ApJ...713L.192G|s2cid=56144432 }} particularly on stars showing solar-like oscillations.{{cite journal |last1=Chaplin |first1=W. J. |date=2010 |title=The asteroseismic potential of Kepler: first results for solar-type stars |arxiv=1001.0506 |display-authors=etal |doi=10.1088/2041-8205/713/2/L169 |volume=713 |issue=2 |journal=The Astrophysical Journal |pages=L169–L175 |bibcode=2010ApJ...713L.169C|s2cid=67758571 }}

File:NASA-KeplerSpaceTelescope-ArtistConcept-20141027.jpg

Once Kepler has collected and sent back the data, raw light curves are constructed. Brightness values are then adjusted to take the brightness variations due to the rotation of the spacecraft into account. The next step is processing (folding) light curves into a more easily observable form and letting software select signals that seem potentially transit-like. At this point, any signal that shows potential transit-like features is called a threshold crossing event. These signals are individually inspected in two inspection rounds, with the first round taking only a few seconds per target. This inspection eliminates erroneously selected non-signals, signals caused by instrumental noise and obvious eclipsing binaries.{{cite web |url=http://exoplanetarchive.ipac.caltech.edu/docs/PurposeOfKOITable.html |title=Purpose of Kepler Objects of Interest (KOI) Activity Tables |website=NASA Exoplanet Archive |publisher=NASA Exoplanet Science Institute}}

Threshold crossing events that pass these tests are called Kepler Objects of Interest (KOI), receive a KOI designation and are archived. KOIs are inspected more thoroughly in a process called dispositioning. Those which pass the dispositioning are called Kepler planet candidates. The KOI archive is not static, meaning that a Kepler candidate could end up in the false-positive list upon further inspection. In turn, KOIs that were mistakenly classified as false positives could end up back in the candidates list.{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/kepler-new-data-q-and-a.html |title=New NASA Kepler Mission Data |date=May 31, 2013 |publisher=NASA |others=NASA Official: Brian Dunbar; Image credit: NASA Ames/W. Stenzel |access-date=April 20, 2014 |type=Interview |first=Michael |last=Haas |archive-url=https://web.archive.org/web/20140420090621/http://www.nasa.gov/mission_pages/kepler/news/kepler-new-data-q-and-a.html |archive-date=April 20, 2014 |url-status=live }}

Not all the planet candidates go through this process. Circumbinary planets do not show strictly periodic transits, and have to be inspected through other methods. In addition, third-party researchers use different data-processing methods, or even search planet candidates from the unprocessed light curve data. As a consequence, those planets may be missing KOI designation.

File:NewKeplerPlanetCandidates-20170619.jpg }}]]

Once suitable candidates have been found from Kepler data, it is necessary to rule out false positives with follow-up tests.

Usually, Kepler candidates are imaged individually with more-advanced ground-based telescopes in order to resolve any background objects which could contaminate the brightness signature of the transit signal.{{cite journal |last1=Batalha |first1=Natalie M. |date=2010 |title=Pre-Spectroscopic False Positive Elimination of Kepler Planet Candidates |arxiv=1001.0392 |display-authors=etal |doi=10.1088/2041-8205/713/2/L103 |volume=713 |issue=2 |journal=The Astrophysical Journal |pages=L103–L108 |bibcode=2010ApJ...713L.103B|s2cid=119236240 }} Another method to rule out planet candidates is astrometry for which Kepler can collect good data even though doing so was not a design goal. While Kepler cannot detect planetary-mass objects with this method, it can be used to determine if the transit was caused by a stellar-mass object.{{cite arXiv |last1=Monet |first1=David G. |date=2010 |title=Preliminary Astrometric Results from Kepler |class=astro-ph.IM |eprint=1001.0305|display-authors=etal}}

There are a few different exoplanet detection methods which help to rule out false positives by giving further proof that a candidate is a real planet. One of the methods, called doppler spectroscopy, requires follow-up observations from ground-based telescopes. This method works well if the planet is massive or is located around a relatively bright star. While current spectrographs are insufficient for confirming planetary candidates with small masses around relatively dim stars, this method can be used to discover additional massive non-transiting planet candidates around targeted stars.{{citation needed|date=March 2022}}

File:329161main fullFFIHot300.png is towards the lower left corner.]]

In multiplanetary systems, planets can often be confirmed through transit timing variation by looking at the time between successive transits, which may vary if planets are gravitationally perturbed by each other. This helps to confirm relatively low-mass planets even when the star is relatively distant. Transit timing variations indicate that two or more planets belong to the same planetary system. There are even cases where a non-transiting planet is also discovered in this way.{{Cite news |url=http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=226 |url-status=dead |archiveurl=https://web.archive.org/web/20130128110114/http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=226 |archivedate=2013-01-28 |title=The Transit Timing Variation (TTV) Planet-finding Technique Begins to Flower |date=2012-08-23 |work=NASA}}

Circumbinary planets show much larger transit timing variations between transits than planets gravitationally disturbed by other planets. Their transit duration times also vary significantly. Transit timing and duration variations for circumbinary planets are caused by the orbital motion of the host stars, rather than by other planets.{{cite arXiv |title=TASTE: The Asiago Survey for Timing transit variations of Exoplanets |eprint=1009.5905 |class=astro-ph.EP |first1=V. |last1=Nascimbeni |first2=G. |last2=Piotto |first3=L. R. |last3=Bedin |first4=M. |last4=Damasso |date=September 29, 2010}} In addition, if the planet is massive enough, it can cause slight variations of the host stars' orbital periods. Despite being harder to find circumbinary planets due to their non-periodic transits, it is much easier to confirm them, as timing patterns of transits cannot be mimicked by an eclipsing binary or a background star system.{{cite journal |title=Kepler-16: A Transiting Circumbinary Planet |journal=Science |first1=Laurance R. |last1=Doyle |first2=Joshua A. |last2=Carter |first3=Daniel C. |last3=Fabrycky |first4=Robert W. |last4=Slawson |first5=Steve B. |last5=Howell |display-authors=etal |volume=333 |issue=6049 |pages=1602–1606 |date=September 2011 |doi=10.1126/science.1210923 |bibcode=2011Sci...333.1602D |arxiv=1109.3432 |pmid=21921192|s2cid=206536332 }}

In addition to transits, planets orbiting around their stars undergo reflected-light variations—like the Moon, they go through phases from full to new and back again. Because Kepler cannot resolve the planet from the star, it sees only the combined light, and the brightness of the host star seems to change over each orbit in a periodic manner. Although the effect is small—the photometric precision required to see a close-in giant planet is about the same as to detect an Earth-sized planet in transit across a solar-type star—Jupiter-sized planets with an orbital period of a few days or less are detectable by sensitive space telescopes such as Kepler. In the long run, this method may help find more planets than the transit method, because the reflected light variation with orbital phase is largely independent of the planet's orbital inclination, and does not require the planet to pass in front of the disk of the star. In addition, the phase function of a giant planet is also a function of its thermal properties and atmosphere, if any. Therefore, the phase curve may constrain other planetary properties, such as the particle size distribution of the atmospheric particles.{{cite journal |last1=Jenkins |first1=J.M. |first2=Laurance R. |last2=Doyle |date=September 20, 2003 |title=Detecting reflected light from close-in giant planets using space-based photometers |journal=Astrophysical Journal |volume=1 |issue=595 |pages=429–445 |doi=10.1086/377165 |bibcode=2003ApJ...595..429J |arxiv=astro-ph/0305473|s2cid=17773111 }}

Kepler's photometric precision is often high enough to observe a star's brightness changes caused by doppler beaming or a star's shape deformation by a companion. These can sometimes be used to rule out hot Jupiter candidates as false positives caused by a star or a brown dwarf when these effects are too noticeable.{{cite journal |title=Validation of Kepler's Multiple Planet Candidates. III: Light Curve Analysis & Announcement of Hundreds of New Multi-planet Systems |arxiv=1402.6534 |first1=Jason F. |last1=Rowe |first2=Stephen T. |last2=Bryson |first3=Geoffrey W. |last3=Marcy |first4=Jack J. |last4=Lissauer |first5=Daniel |last5=Jontof-Hutter |first6=Fergal |last6=Mullally |first7=Ronald L. |last7=Gilliland |first8=Howard |last8=Issacson |first9=Eric |last9=Ford |first10=Steve B. |last10=Howell |first11=William J. |last11=Borucki |first12=Michael |last12=Haas |first13=Daniel |last13=Huber |first14=Jason H. |last14=Steffen |first15=Susan E. |last15=Thompson |first16=Elisa |last16=Quintana |first17=Thomas |last17=Barclay |first18=Martin |last18=Still |first19=Jonathan |last19=Fortney |first20=T. N. |last20=Gautier III |first21=Roger |last21=Hunter |first22=Douglas A. |last22=Caldwell |first23=David R. Ciardi Edna |last23=Devore |first24=William |last24=Cochran |first25=Jon |last25=Jenkins |first26=Eric |last26=Agol |first27=Joshua A. |last27=Carter |first28=John |last28=Geary |display-authors=5 |date=February 26, 2014 |doi=10.1088/0004-637X/784/1/45 |volume=784 |issue=1 |journal=The Astrophysical Journal |page=45 |bibcode=2014ApJ...784...45R|s2cid=119118620 }} However, there are some cases where such effects are detected even by planetary-mass companions such as TrES-2b.{{cite journal |title=A comprehensive study of Kepler phase curves and secondary eclipses – temperatures and albedos of confirmed Kepler giant planets |arxiv=1404.4348 |first1=Daniel |last1=Angerhausen |first2=Emily |last2=DeLarme |first3=Jon A. |last3=Morse |date=April 16, 2014 |doi=10.1086/683797 |volume=127 |issue=957 |journal=Publications of the Astronomical Society of the Pacific |pages=1113–1130 |bibcode=2015PASP..127.1113A|s2cid=118462488 }}

If a planet cannot be detected through at least one of the other detection methods, it can be confirmed by determining if the possibility of a Kepler candidate being a real planet is significantly larger than any false-positive scenarios combined. One of the first methods was to see if other telescopes can see the transit as well. The first planet confirmed through this method was Kepler-22b which was also observed with the Spitzer Space Telescope in addition to analyzing any other false-positive possibilities.{{Cite news |date=December 5, 2011 |title=Kepler 22-b: Earth-like planet confirmed |url=https://www.bbc.co.uk/news/science-environment-16040655 |url-status=live |archive-url=https://web.archive.org/web/20240106205847/https://www.bbc.com/news/science-environment-16040655 |archive-date=January 6, 2024 |access-date=December 6, 2011 |work=BBC Online }} Such confirmation is costly, as small planets can generally be detected only with space telescopes.

In 2014, a new confirmation method called "validation by multiplicity" was announced. From the planets previously confirmed through various methods, it was found that planets in most planetary systems orbit in a relatively flat plane, similar to the planets found in the Solar System. This means that if a star has multiple planet candidates, it is very likely a real planetary system. Transit signals still need to meet several criteria which rule out false-positive scenarios. For instance, it has to have considerable signal-to-noise ratio, it has at least three observed transits, orbital stability of those systems have to be stable and transit curve has to have a shape that partly eclipsing binaries could not mimic the transit signal. In addition, its orbital period needs to be 1.6 days or longer to rule out common false positives caused by eclipsing binaries.{{cite journal |title=Validation of Kepler's Multiple Planet Candidates. II: Refined Statistical Framework and Descriptions of Systems of Special Interest |arxiv=1402.6352 |last1=Lissauer |first1=Jack J. |last2=Marcy |first2=Geoffrey W. |last3=Bryson |first3=Stephen T. |last4=Rowe |first4=Jason F. |last5=Jontof-Hutter |first5=Daniel |last6=Agol |first6=Eric |last7=Borucki |first7=William J. |last8=Carter |first8=Joshua A. |last9=Ford |first9=Eric B. |last10=Gilliland |first10=Ronald L. |last11=Kolbl |first11=Rea |last12=Star |first12=Kimberly M. |last13=Steffen |first13=Jason H. |last14=Torres |first14=Guillermo |display-authors=5 |date=February 25, 2014 |doi=10.1088/0004-637X/784/1/44 |volume=784 |issue=1 |journal=The Astrophysical Journal |page=44 |bibcode=2014ApJ...784...44L|s2cid=119108651 }} Validation by multiplicity method is very efficient and allows to confirm hundreds of Kepler candidates in a relatively short amount of time.

A new validation method using a tool called PASTIS has been developed. It makes it possible to confirm a planet even when only a single candidate transit event for the host star has been detected. A drawback of this tool is that it requires a relatively high signal-to-noise ratio from Kepler data, so it can mainly confirm only larger planets or planets around quiet and relatively bright stars. Currently, the analysis of Kepler candidates through this method is underway.{{cite journal |title=PASTIS: Bayesian Extrasolar Planet Validation. I. General Framework, Models, and Performance |arxiv=1403.6725 |last1=Díaz |first1=Rodrigo F. |last2=Almenara |first2=José M. |last3=Santerne |first3=Alexandre |last4=Moutou |first4=Claire |last5=Lethuillier |first5=Anthony |last6=Deleuil |first6=Magali |date=March 26, 2014 |doi=10.1093/mnras/stu601 |volume=441 |issue=2 |journal=Monthly Notices of the Royal Astronomical Society |pages=983–1004 |doi-access=free |bibcode=2014MNRAS.441..983D|s2cid=118387716 }} PASTIS was first successful for validating the planet Kepler-420b.{{cite journal |title=SOPHIE Velocimetry of Kepler Transit Candidates: XII. KOI-1257 b: A Highly-Eccentric 3-Month Period Transiting Exoplanet |arxiv=1406.6172 |last1=Santerne |first1=A. |last2=Hébrard |first2=G. |last3=Deleuil |first3=M. |last4=Havel |first4=M. |last5=Correia |first5=A. C. M. |last6=Almenara |first6=J. -M. |last7=Alonso |first7=R. |last8=Arnold |first8=L. |last9=Barros |first9=S. C. C. |last10=Behrend |first10=R. |last11=Bernasconi |first11=L. |last12=Boisse |first12=I. |last13=Bonomo |first13=A. S. |last14=Bouchy |first14=F. |last15=Bruno |first15=G. |last16=Damiani |first16=C. |last17=Díaz |first17=R. F. |last18=Gravallon |first18=D. |last19=Guillot |first19=T. |last20=Labrevoir |first20=O. |last21=Montagnier |first21=G. |last22=Moutou |first22=C. |last23=Rinner |first23=C. |last24=Santos |first24=N. C. |last25=Abe |first25=L. |last26=Audejean |first26=M. |last27=Bendjoya |first27=P. |last28=Gillier |first28=C. |last29=Gregorio |first29=J. |last30=Martinez |first30=P. |last31=Michelet |first31=J. |last32=Montaigut |first32=R. |last33=Poncy |first33=R. |last34=Rivet |first34=J. -P. |last35=Rousseau |first35=G. |last36=Roy |first36=R. |last37=Suarez |first37=O. |last38=Vanhuysse |first38=M. |last39=Verilhac |first39=D. |display-authors=5 |date=June 24, 2014 |doi=10.1051/0004-6361/201424158 |volume=571 |journal=Astronomy & Astrophysics |page=A37 |bibcode=2014A&A...571A..37S|s2cid=118582477 }}

File:Neighborhood21.gif

In April 2012, an independent panel of senior NASA scientists recommended that the Kepler mission be continued through 2016. According to the senior review, Kepler observations needed to continue until at least 2015 to achieve all the stated scientific goals.{{Cite news |last=Clark |first=Stephen |date=April 4, 2012 |title=Kepler planet-hunting mission extended until 2016 |url=https://www.spaceflightnow.com/news/n1204/04kepler/ |url-status=live |archive-url=https://web.archive.org/web/20240222133840/https://www.spaceflightnow.com/news/n1204/04kepler/ |archive-date=February 22, 2024 |access-date=April 4, 2012 |work=Spaceflight Now }} On November 14, 2012, NASA announced the completion of Kepler's primary mission, and the beginning of its extended mission, which ended in 2018 when it ran out of fuel.{{cite web |title=Release : 12–394 – NASA's Kepler Completes Prime Mission, Begins Extended Mission |url=http://www.nasa.gov/home/hqnews/2012/nov/HQ_12-394_Kepler_Completes_Prime_Mission.html |publisher=NASA |access-date=November 17, 2012 |archive-date=July 31, 2020 |archive-url=https://web.archive.org/web/20200731161518/https://www.nasa.gov/home/hqnews/2012/nov/HQ_12-394_Kepler_Completes_Prime_Mission.html |url-status=dead }}

In July 2012, one of Kepler's four reaction wheels (wheel 2) failed. On May 11, 2013, a second wheel (wheel 4) failed, jeopardizing the continuation of the mission, as three wheels are necessary for its planet hunting. Kepler had not collected science data since May because it was not able to point with sufficient accuracy. On July 18 and 22 reaction wheels 4 and 2 were tested respectively; wheel 4 only rotated counter-clockwise but wheel 2 ran in both directions, albeit with significantly elevated friction levels.{{cite web |title=Kepler Mission Manager Update: Initial Recovery Tests |url=http://www.nasa.gov/content/kepler-mission-manager-update-initial-recovery-tests/ |publisher=NASA |access-date=September 9, 2013 |date=July 24, 2013 |archive-date=September 22, 2020 |archive-url=https://web.archive.org/web/20200922073835/https://www.nasa.gov/content/kepler-mission-manager-update-initial-recovery-tests/ |url-status=dead }} A further test of wheel 4 on July 25 managed to achieve bi-directional rotation.{{cite web |url=http://www.nasa.gov/content/kepler-mission-manager-update-pointing-test |title=Kepler Mission Manager Update: Pointing Test |date=August 2, 2013 |publisher=NASA |access-date=August 3, 2013 |archive-date=July 25, 2020 |archive-url=https://web.archive.org/web/20200725185646/https://www.nasa.gov/content/kepler-mission-manager-update-pointing-test/ |url-status=dead }} Both wheels, however, exhibited too much friction to be useful. On August 2, NASA put out a call for proposals to use the remaining capabilities of Kepler for other scientific missions. Starting on August 8, a full systems evaluation was conducted. It was determined that wheel 2 could not provide sufficient precision for scientific missions and the spacecraft was returned to a "rest" state to conserve fuel. Wheel 4 was previously ruled out because it exhibited higher friction levels than wheel 2 in previous tests. Sending astronauts to fix Kepler is not an option because it orbits the Sun and is millions of kilometers from Earth.

On August 15, 2013, NASA announced that Kepler would not continue searching for planets using the transit method after attempts to resolve issues with two of the four reaction wheels failed. An engineering report was ordered to assess the spacecraft's capabilities, its two good reaction wheels and its thrusters. Concurrently, a scientific study was conducted to determine whether enough knowledge can be obtained from Kepler's limited scope to justify its $18 million per year cost.

Possible ideas included searching for asteroids and comets, looking for evidence of supernovas, and finding huge exoplanets through gravitational microlensing. Another proposal was to modify the software on Kepler to compensate for the disabled reaction wheels. Instead of the stars being fixed and stable in Kepler's field of view, they will drift. Proposed software was to track this drift and more or less completely recover the mission goals despite being unable to hold the stars in a fixed view.{{cite arXiv |title=KeSeF - Kepler Self Follow-up Mission |eprint=1308.2252 |class=astro-ph.EP |first=Aviv |last=Ofir |date=August 9, 2013}}

Previously collected data continued to be analyzed.{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20130607.html |title=Kepler Mission Manager Update |date=June 7, 2013 |publisher=NASA |access-date=June 14, 2013 |archive-date=July 31, 2020 |archive-url=https://web.archive.org/web/20200731222857/https://www.nasa.gov/mission_pages/kepler/news/keplerm-20130607.html |url-status=dead }}

In November 2013, a new mission plan named K2 "Second Light" was presented for consideration.{{cite web |last1=Johnson |first1=Michele |editor1-last=Johnson |editor1-first=Michele |title=A Sunny Outlook for NASA Kepler's Second Light |url=http://www.nasa.gov/kepler/a-sunny-outlook-for-nasa-keplers-second-light |date=November 25, 2013 |publisher=NASA |access-date=December 12, 2013 |archive-url=https://web.archive.org/web/20140418000640/http://www.nasa.gov/kepler/a-sunny-outlook-for-nasa-keplers-second-light/ |archive-date=April 18, 2014 |url-status=live |others=NASA Official: Brian Dunbar; Image credits: NASA Ames; NASA Ames/W Stenzel }}{{cite web |last1=Johnson |first1=Michele |editor1-last=Johnson |editor1-first=Michele |title=Kepler's Second Light: How K2 Will Work |publisher=NASA |date=December 11, 2013 |url=http://www.nasa.gov/kepler/keplers-second-light-how-k2-will-work/ |access-date=December 12, 2013 |others=NASA Official: Brian Dunbar; Image credit: NASA Ames/W Stenzel |archive-url=https://web.archive.org/web/20140418001138/http://www.nasa.gov/kepler/keplers-second-light-how-k2-will-work/ |archive-date=April 18, 2014 |url-status=live }}{{cite web |first=Roger |last=Hunter |editor1-last=Johnson |editor1-first=Michele |title=Kepler Mission Manager Update: Invited to 2014 Senior Review |publisher=NASA |date=December 11, 2013 |url=http://www.nasa.gov/kepler/kepler-mission-manager-update-invited-to-2014-senior-review |access-date=December 12, 2013 |others=NASA Official: Brian Dunbar |archive-url=https://web.archive.org/web/20140418001405/http://www.nasa.gov/kepler/kepler-mission-manager-update-invited-to-2014-senior-review/ |archive-date=April 18, 2014 |url-status=live }}{{cite web |last=Wall |first=Mike |title=NASA's Hobbled Planet-Hunting Spacecraft May Resume Search for Alien Worlds |work=Space.com |publisher=TechMediaNetwork |date=November 5, 2013 |url=http://www.space.com/23465-planet-hunting-kepler-spacecraft-future.html |access-date=April 17, 2014 |others=Image credit: NASA |archive-url=https://web.archive.org/web/20140418002147/http://www.space.com/23465-planet-hunting-kepler-spacecraft-future.html |archive-date=April 18, 2014 |url-status=live }} K2 would involve using Kepler's remaining capability, photometric precision of about 300 parts per million, compared with about 20 parts per million earlier, to collect data for the study of "supernova explosions, star formation and Solar-System bodies such as asteroids and comets, ... " and for finding and studying more exoplanets. In this proposed mission plan, Kepler would search a much larger area in the plane of Earth's orbit around the Sun. Celestial objects, including exoplanets, stars and others, detected by the K2 mission would be associated with the EPIC acronym, standing for Ecliptic Plane Input Catalog.

{{wide image|Kepler-K2-MissionTimeline-20140808.png|800px|align-cap=center|K2 mission timeline (August 8, 2014).{{cite web |title=Kepler Mission Manager Update: K2 collecting data |url=http://www.nasa.gov/ames/kepler/kepler-mission-manager-update-k2-collecting-data/ |date=August 8, 2014 |publisher=NASA |access-date=August 9, 2014 |archive-date=May 10, 2020 |archive-url=https://web.archive.org/web/20200510081119/https://www.nasa.gov/ames/kepler/kepler-mission-manager-update-k2-collecting-data/ |url-status=dead }}}}

In early 2014, the spacecraft underwent successful testing for the K2 mission.{{cite web |url=http://www.nasa.gov/ames/kepler/kepler-mission-manager-update-k2-spacecraft-operation-tests-continue/ |title=Kepler Mission Manager Update: K2 spacecraft operation tests continue |publisher=NASA |date=February 14, 2014 |access-date=April 17, 2014 |first=Roger |last=Hunter |editor1-last=Johnson |editor1-first=Michele |others=NASA Official: Brian Dunbar; Image Credit: NASA Ames/T. Barclay |archive-url=https://web.archive.org/web/20140418002638/http://www.nasa.gov/ames/kepler/kepler-mission-manager-update-k2-spacecraft-operation-tests-continue/ |archive-date=April 18, 2014 |url-status=live }} From March to May 2014, data from a new field called Field 0 was collected as a testing run.{{cite journal |title=HAT-P-54b: A hot jupiter transiting a 0.64 Msun star in field 0 of the K2 mission |arxiv=1404.4417 |first1=G. Á. |last1=Bakos |first2=J. D. |last2=Hartman |first3=W. |last3=Bhatti |first4=A. |last4=Bieryla |first5=M. |last5=de Val-Borro |first6=D. W. |last6=Latham |first7=L. A. |last7=Buchhave |first8=Z. |last8=Csubry |first9=K. |last9=Penev |first10=G. |last10=Kovács |first11=B. |last11=Béky |first12=E. |last12=Falco |first13=T. |last13=Kovács |first14=A. W. |last14=Howard |first15=J. A. |last15=Johnson |first16=H. |last16=Isaacson |first17=G. W. |last17=Marcy |first18=G. |last18=Torres |first19=R. W. |last19=Noyes |first20=P. |last20=Berlind |first21=M. L. |last21=Calkins |first22=G. A. |last22=Esquerdo |first23=J. |last23=Lázár |first24=I. |last24=Papp |first25=P. |last25=Sári |display-authors=5 |date=April 17, 2014 |doi=10.1088/0004-6256/149/4/149 |volume=149 |issue=4 |journal=The Astronomical Journal |page=149 |bibcode=2015AJ....149..149B|s2cid=119239193 }} On May 16, 2014, NASA announced the approval of extending the Kepler mission to the K2 mission. Kepler's photometric precision for the K2 mission was estimated to be 50 ppm on a magnitude 12 star for a 6.5-hour integration.{{cite web |url=http://keplerscience.arc.nasa.gov/K2/ |title=Kepler Guest Observer Program |publisher=NASA |date=May 29, 2014 |access-date=June 12, 2014 |editor1-first=Martin |editor1-last=Still |others=NASA Official: Jessie Dotson |archive-url=https://web.archive.org/web/20140613045308/http://keplerscience.arc.nasa.gov/K2/ |archive-date=June 13, 2014 |url-status=dead }} In February 2014, photometric precision for the K2 mission using two-wheel, fine-point precision operations was measured as 44 ppm on magnitude 12 stars for a 6.5-hour integration. The analysis of these measurements by NASA suggests the K2 photometric precision approaches that of the Kepler archive of three-wheel, fine-point precision data.{{cite web |url=http://keplerscience.arc.nasa.gov/K2/Performance.shtml |title=K2 Performance |publisher=NASA |date=May 29, 2014 |access-date=June 12, 2014 |editor1-first=Martin |editor1-last=Still |others=NASA Official: Jessie Dotson |archive-url=https://web.archive.org/web/20140613045540/http://keplerscience.arc.nasa.gov/K2/Performance.shtml |archive-date=June 13, 2014 |url-status=dead }}

On May 29, 2014, campaign fields 0 to 13 were reported and described in detail.

File:NASA-KeplerSecondLight-K2-Explained-20131211.jpg

Field 1 of the K2 mission is set towards the Leo-Virgo region of the sky, while Field 2 is towards the "head" area of Scorpius and includes two globular clusters, Messier 4 and Messier 80,{{Cite journal |title=Cepheids and RR Lyrae Stars in the K2 Fields |journal=Information Bulletin on Variable Stars |first1=L. |last1=Molnár |first2=E. |last2=Plachy |first3=R. |last3=Szabó |volume=6108 |issue=1 |pages=1 |date=May 29, 2014 |bibcode=2014IBVS.6108....1M |arxiv=1405.7690}} and part of the Scorpius–Centaurus association, which is only about 11 million years old{{Cite journal |first1=Mark J. |last1=Pecaut |first2=Eric E. |last2=Mamajek |first3=Eric J. |last3=Bubar |date=February 2012 |title=A Revised Age for Upper Scorpius and the Star Formation History among the F-type Members of the Scorpius-Centaurus OB Association |journal=Astrophysical Journal |volume=746 |issue=2 |pages=154 |arxiv=1112.1695 |bibcode=2012ApJ...746..154P |doi=10.1088/0004-637X/746/2/154|s2cid=118461108 }} and {{convert|380|-|470|ly|pc|order=flip|lk=on}} distant{{cite journal |title=A Hipparcos Census of Nearby OB Associations |first1=P. T. |last1=de Zeeuw |first2=R. |last2=Hoogerwerf |first3=J. H. J. |last3=de Bruijne |first4=A. G. A. |last4=Brown |first5=A. |last5=Blaauw |date=1999 |journal=Astronomical Journal |volume=117 |issue=1 |pages=354–399 |bibcode=1999AJ....117..354D |doi=10.1086/300682 |arxiv=astro-ph/9809227 |s2cid=16098861 }} with probably over 1,000 members.{{cite journal |bibcode=2002AJ....124.1670M |first1=E. E. |last1=Mamajek |first2=M. R. |last2=Meyer |first3=James |last3=Liebert |date=2002 |journal=Astronomical Journal |volume=124 |issue=3 |pages=1670–1694 |title=Post-T Tauri Stars in the Nearest OB Association |doi=10.1086/341952 |arxiv=astro-ph/0205417|s2cid=16855894 }}

On December 18, 2014, NASA announced that the K2 mission had detected its first confirmed exoplanet, a super-Earth named HIP 116454 b. Its signature was found in a set of engineering data meant to prepare the spacecraft for the full K2 mission. Radial velocity follow-up observations were needed as only a single transit of the planet was detected.{{Cite press release |last1=Chou |first1=Felicia |last2=Johnson |first2=Michele |date=December 18, 2014 |title=NASA's Kepler Reborn, Makes First Exoplanet Find of New Mission |url=https://www.nasa.gov/news-release/nasas-kepler-reborn-makes-first-exoplanet-find-of-new-mission/ |url-status=live |archive-url=https://web.archive.org/web/20240929011713/https://www.nasa.gov/news-release/nasas-kepler-reborn-makes-first-exoplanet-find-of-new-mission/ |archive-date=September 29, 2024 |access-date=December 19, 2014 |publisher=NASA |id=Release 14-335 }}

During a scheduled contact on April 7, 2016, Kepler was found to be operating in emergency mode, the lowest operational and most fuel intensive mode. Mission operations declared a spacecraft emergency, which afforded them priority access to NASA's Deep Space Network.{{cite web |url=http://www.nasa.gov/feature/mission-manager-update-kepler-recovered-from-emergency-and-stable |title=Mission Manager Update: Kepler Recovered from Emergency and Stable |publisher=NASA |first=Charlie |last=Sobeck |date=April 11, 2016 |access-date=April 14, 2016 |archive-date=November 8, 2020 |archive-url=https://web.archive.org/web/20201108122748/http://www.nasa.gov/feature/mission-manager-update-kepler-recovered-from-emergency-and-stable/ |url-status=dead }}{{Cite journal |last=Witze |first=Alexandra |date=April 10, 2016 |title=Kepler spacecraft in emergency mode |url=https://www.nature.com/articles/nature.2016.19720 |url-status=live |journal=Nature |doi=10.1038/nature.2016.19720 |issn=0028-0836 |eissn=1476-4687 |archive-url=https://web.archive.org/web/20240701063547/https://www.nature.com/articles/nature.2016.19720 |archive-date=July 1, 2024 |access-date=April 14, 2016 |doi-access=free }} By the evening of April 8 the spacecraft had been upgraded to safe mode, and on April 10 it was placed into point-rest state,{{Cite news |last=Khan |first=Amina |date=April 11, 2016 |title=NASA Kepler spacecraft recovers from emergency mode, but what triggered it? |url=https://www.latimes.com/science/sciencenow/la-sci-sn-nasa-kepler-emergency-safe-20160411-story.html |url-status=live |archive-url=https://web.archive.org/web/20240429083943/https://www.latimes.com/science/sciencenow/la-sci-sn-nasa-kepler-emergency-safe-20160411-story.html |archive-date=April 29, 2024 |access-date=April 14, 2016 |work=Los Angeles Times }} a stable mode which provides normal communication and the lowest fuel burn. At that time, the cause of the emergency was unknown, but it was not believed that Kepler's reaction wheels or a planned maneuver to support K2{{'s}} Campaign 9 were responsible. Operators downloaded and analyzed engineering data from the spacecraft, with the prioritization of returning to normal science operations.{{Cite news |last=Clark |first=Stephen |date=April 11, 2016 |title=Kepler telescope recovered from spacecraft emergency |url=https://spaceflightnow.com/2016/04/11/kepler-telescope-recovered-from-spacecraft-emergency/ |url-status=live |archive-url=https://web.archive.org/web/20240619095918/https://spaceflightnow.com/2016/04/11/kepler-telescope-recovered-from-spacecraft-emergency/ |archive-date=June 19, 2024 |access-date=April 14, 2016 |work=Spaceflight Now }} Kepler was returned to science mode on April 22.{{cite web |url=https://www.nasa.gov/feature/ames/kepler/mission-manager-qa-recovering-the-kepler-spacecraft-to-hunt-for-exoplanets-again |title=Mission Manager Q&A: Recovering The Kepler Spacecraft To Hunt For Exoplanets Again |publisher=NASA |first1=Michele |last1=Johnson |first2=Charlie |last2=Sobeck |date=May 3, 2016 |access-date=August 25, 2016 |archive-date=November 8, 2020 |archive-url=https://web.archive.org/web/20201108113948/http://www.nasa.gov/feature/ames/kepler/mission-manager-qa-recovering-the-kepler-spacecraft-to-hunt-for-exoplanets-again/ |url-status=dead }} The emergency caused the first half of Campaign 9 to be shortened by two weeks.{{cite web |url=https://www.nasa.gov/feature/ames/kepler/mission-manager-update-k2-marches-on |title=Mission Manager Update: K2 Marches On |publisher=NASA |first1=Michele |last1=Johnson |first2=Charlie |last2=Sobeck |date=June 9, 2016 |access-date=August 25, 2016 |archive-date=November 8, 2020 |archive-url=https://web.archive.org/web/20201108161812/http://www.nasa.gov/feature/ames/kepler/mission-manager-update-k2-marches-on/ |url-status=dead }}

In June 2016, NASA announced a K2 mission extension of three additional years, beyond the expected exhaustion of on-board fuel in 2018.{{cite web |url=http://keplerscience.arc.nasa.gov/k2-mission-officially-extended-through-end-of-mission.html |archive-url=https://web.archive.org/web/20160814044546/http://keplerscience.arc.nasa.gov/k2-mission-officially-extended-through-end-of-mission.html |url-status=dead |archive-date=August 14, 2016 |title=K2 mission officially extended through end of mission |publisher=NASA |first=Knicole |last=Colon |date=June 9, 2016 |access-date=August 25, 2016}} In August 2018, NASA roused the spacecraft from sleep mode, applied a modified configuration to deal with thruster problems that degraded pointing performance, and began collecting scientific data for the 19th observation campaign, finding that the onboard fuel was not yet utterly exhausted.{{cite web|url=https://www.nasa.gov/ames/kepler/kepler-spacecraft-updates|title=Kepler and K2|website=Kepler Spacecraft Updates|date=September 5, 2018|access-date=September 7, 2018|archive-date=November 9, 2020|archive-url=https://web.archive.org/web/20201109033018/https://www.nasa.gov/ames/kepler/kepler-spacecraft-updates/|url-status=dead}}

On October 30, 2018, NASA announced that the spacecraft was out of fuel and its mission was officially ended.{{Cite news |last=Griggs |first=Mary Beth |date=October 30, 2018 |title=The Kepler Space Telescope is dead |url=https://www.theverge.com/2018/10/30/18044152/nasa-kepler-space-telescope-out-of-fuel-dead |url-status=live |archive-url=https://web.archive.org/web/20240410094743/https://www.theverge.com/2018/10/30/18044152/nasa-kepler-space-telescope-out-of-fuel-dead |archive-date=April 10, 2024 |work=The Verge }}

File:NGC 6791 cluster.jpg NGC 6791. Celestial north is towards the lower left corner.]]

File:Kepler First Light Detail TrES-2.jpg is towards the lower left corner.]]

The Kepler space telescope was in active operation from 2009 through 2013, with the first main results announced on January 4, 2010. As expected, the initial discoveries were all short-period planets. As the mission continued, additional longer-period candidates were found. {{As of|2018|11}}, Kepler has discovered 5,011 exoplanet candidates and 2,662 confirmed exoplanets.{{cite web |url=https://www.nasa.gov/kepler/discoveries |title=How many exoplanets has Kepler discovered? |publisher=NASA |date=October 27, 2017 |access-date=October 28, 2017}}

{{Cite web |date=November 2, 2018 |title=Kepler by the Numbers |url=https://www.nasa.gov/image-article/kepler-by-numbers-mission-statistics/ |url-status=live |archive-url=https://web.archive.org/web/20240422001857/https://www.nasa.gov/image-article/kepler-by-numbers-mission-statistics/ |archive-date=April 22, 2024 |access-date=September 10, 2021 |publisher=NASA }} As of August 2022, 2,056 exoplanet candidates remain to be confirmed and 2,711 are now confirmed exoplanets.{{Cite web |title=Exoplanet and Candidate Statistics |url=https://exoplanetarchive.ipac.caltech.edu/docs/counts_detail.html |access-date=2022-08-26 |website=exoplanetarchive.ipac.caltech.edu}}

NASA held a press conference to discuss early science results of the Kepler mission on August 6, 2009.{{cite web |url=http://www.nasa.gov/centers/ames/news/releases/2009/M09-94AR.html |title=NASA Announces Briefing About Kepler's Early Science Results |date=August 3, 2009 |publisher=NASA |access-date=April 23, 2011 |archive-date=May 11, 2020 |archive-url=https://web.archive.org/web/20200511182808/https://www.nasa.gov/centers/ames/news/releases/2009/M09-94AR.html |url-status=dead }} At this press conference, it was revealed that Kepler had confirmed the existence of the previously known transiting exoplanet HAT-P-7b, and was functioning well enough to discover Earth-size planets.{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/kepler-discovery.html |title=NASA's Kepler Spies Changing Phases on a Distant World |date=August 6, 2009 |publisher=NASA |access-date=August 6, 2009 |archive-date=April 18, 2020 |archive-url=https://web.archive.org/web/20200418042038/https://www.nasa.gov/mission_pages/kepler/news/kepler-discovery.html |url-status=dead }}{{cite journal |title=Kepler's Optical Phase Curve of the Exoplanet HAT-P-7b |journal=Science |date=August 7, 2009 |publisher=AAAS |location=Washington, DC |issn=1095-9203 |oclc=1644869 |volume=325 |issue=5941 |page=709 |doi=10.1126/science.1178312 |pmid=19661420 |bibcode=2009Sci...325..709B |first1=W. J. |last1=Borucki |first2=D. |last2=Koch |first3=J. |last3=Jenkins |first4=D. |last4=Sasselov |first5=R. |last5=Gilliland |first6=N. |last6=Batalha |first7=D. W. |last7=Latham |first8=D. |last8=Caldwell |first9=G. |last9=Basri |first10=T. |last10=Brown |first11=J. |last11=Christensen-Dalsgaard |first12=W. D. |last12=Cochran |first13=E. |last13=Devore |first14=E. |last14=Dunham |first15=A. K. |last15=Dupree |first16=T. |last16=Gautier |first17=J. |last17=Geary |first18=A. |last18=Gould |first19=S. |last19=Howell |first20=H. |last20=Kjeldsen |first21=J. |last21=Lissauer |first22=G. |last22=Marcy |first23=S. |last23=Meibom |first24=D. |last24=Morrison |first25=J. |last25=Tarter |s2cid=206522122 |display-authors=5 |url=https://zenodo.org/record/1230908 }}

Because Kepler's detection of planets depends on seeing very small changes in brightness, stars that vary in brightness by themselves (variable stars) are not useful in this search. From the first few months of data, Kepler scientists determined that about 7,500 stars from the initial target list are such variable stars. These were dropped from the target list, and replaced by new candidates. On November 4, 2009, the Kepler project publicly released the light curves of the dropped stars.{{Cite web |date=November 4, 2009 |title=Kepler dropped stars now public |url=https://archive.stsci.edu/mast_news.php?out=html&desc=t&id=342 |url-status=live |archive-url=https://web.archive.org/web/20240707015652/https://archive.stsci.edu/mast_news.php?out=html&desc=t&id=342 |archive-date=July 7, 2024 |access-date=April 23, 2011 |publisher=NASA }} The first new planet candidate observed by Kepler was originally marked as a false positive because of uncertainties in the mass of its parent star. However, it was confirmed ten years later and is now designated Kepler-1658b.{{cite journal |last1=Chontos |first1=Ashley |last2=Huber |first2=Daniel |last3=Latham |first3=David W. |last4=Bieryla |first4=Allyson |last5=van Eylen |first5=Vincent |last6=Bedding |first6=Timothy R. |last7=Berger |first7=Travis |last8=Buchhave |first8=Lars A. |last9=Campante |first9=Tiago L. |last10=Chaplin |first10=William J |last11=Colman |first11=Isabel L. |last12=Coughlin |first12=Jeff L. |last13=Davies |first13=Guy |last14=Hirano |first14=Teruyuki |last15=Howard |first15=Andrew W. |last16=Isaacson |first16=Howard |title=The Curious Case of KOI 4: Confirming Kepler's First Exoplanet Detection|journal=The Astronomical Journal |volume=157 |issue=5 |pages=192 |arxiv=1903.01591 |date=March 2019 |doi=10.3847/1538-3881/ab0e8e |bibcode=2019AJ....157..192C |s2cid=119240124 |doi-access=free }}{{Cite press release |last1=Chen |first1=Rick |date=March 5, 2019 |title=Kepler's First Planet Candidate Confirmed 10 Years Later |url=https://www.nasa.gov/missions/kepler/discovery-alert-keplers-first-planet-candidate-confirmed-10-years-later/ |url-status=live |archive-url=https://web.archive.org/web/20231011101850/https://www.nasa.gov/missions/kepler/discovery-alert-keplers-first-planet-candidate-confirmed-10-years-later/ |archive-date=October 11, 2023 |access-date=March 6, 2019 |publisher=NASA }}

The first six weeks of data revealed five previously unknown planets, all very close to their stars.{{cite web |url=http://www.sciencenews.org/view/generic/id/52465/title/Kepler_space_telescope_finds_its_first_extrasolar_planets |title=Kepler space telescope finds its first extrasolar planets |publisher=Sciencenews.org |date=January 30, 2010 |access-date=February 5, 2011 |archive-date=September 25, 2012 |archive-url=https://web.archive.org/web/20120925002416/http://www.sciencenews.org/view/generic/id/52465/title/Kepler_space_telescope_finds_its_first_extrasolar_planets |url-status=dead }}{{cite web |last=MacRobert |first=Robert |title=Kepler's First Exoplanet Results – News Blog |url=http://www.skyandtelescope.com/community/skyblog/newsblog/80621797.html |publisher=Sky & Telescope |date=January 4, 2010 |access-date=April 21, 2011 |archive-date=September 14, 2011 |archive-url=https://web.archive.org/web/20110914041857/http://www.skyandtelescope.com/community/skyblog/newsblog/80621797.html |url-status=dead }} Among the notable results are one of the least dense planets yet found,{{cite web |last=Gilster |first=Paul |url=http://www.centauri-dreams.org/?p=16640 |title=The Remarkable Kepler-11 |publisher=Tau Zero Foundation |date=February 2, 2011 |access-date=April 21, 2011}} two low-mass white dwarfs{{cite journal |first1=Marten H. |last1=van Kerkwijk |first2=Saul A. |last2=Rappaport |first3=René P. |last3=Breton |first4=Stephen |last4=Justham |first5=Philipp |last5=Podsiadlowski |first6=Zhanwen |last6=Han |title=Observations of Doppler Boosting in Kepler Light Curves |date=May 20, 2010 |journal=The Astrophysical Journal |issn=0004-637X |volume=715 |issue=1 |pages=51–58 |bibcode=2010ApJ...715...51V |doi=10.1088/0004-637X/715/1/51 |arxiv=1001.4539|s2cid=15893663 }} that were initially reported as being members of a new class of stellar objects,{{cite web |last=Villard |first=Ray |title=Blazing Stellar Companion Defies Explanation |url=http://news.discovery.com/space/blazing-stellar-companion-defies-explanation.html |publisher=Discovery.com |access-date=April 20, 2011 |archive-date=March 2, 2012 |archive-url=https://web.archive.org/web/20120302113859/http://news.discovery.com/space/blazing-stellar-companion-defies-explanation.html |url-status=dead }} and Kepler-16b, a well-characterized planet orbiting a binary star.

On June 15, 2010, the Kepler mission released data on all but 400 of the ~156,000 planetary target stars to the public. 706 targets from this first data set have viable exoplanet candidates, with sizes ranging from as small as Earth to larger than Jupiter. The identity and characteristics of 306 of the 706 targets were given. The released targets included five{{citation needed|date=May 2016}} candidate multi-planet systems, including six extra exoplanet candidates. Only 33.5 days of data were available for most of the candidates. NASA also announced data for another 400 candidates were being withheld to allow members of the Kepler team to perform follow-up observations.{{cite web |title=Kepler News: First 43 Days of Kepler Data Released |url=http://kepler.arc.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=42 |archive-url=https://web.archive.org/web/20100811220422/http://www.kepler.arc.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=42 |url-status=dead |archive-date=August 11, 2010 |publisher=NASA |date=May 15, 2010 |access-date=April 24, 2011}} The data for these candidates was published February 2, 2011. (See the Kepler results for 2011 below.)

The Kepler results, based on the candidates in the list released in 2010, implied that most candidate planets have radii less than half that of Jupiter. The results also imply that small candidate planets with periods less than thirty days are much more common than large candidate planets with periods less than thirty days and that the ground-based discoveries are sampling the large-size tail of the size distribution.{{cite report |last1=Borucki |first1=William J. |display-authors=etal|title=Characteristics of Kepler Planetary Candidates Based on the First Data Set: The Majority are Found to be Neptune-Size and Smaller |arxiv=1006.2799 |date=2010 |doi=10.1088/0004-637X/728/2/117 |s2cid=93116 }} This contradicted older theories which had suggested small and Earth-size planets would be relatively infrequent.{{cite journal |last1=Woolfson |first1=M. M. |title=The Solar System: Its Origin and Evolution |journal=Journal of the Royal Astronomical Society |volume=34 |pages=1–20 |date=1993 |bibcode=1993QJRAS..34....1W}} Page 18 in particular states that models that required a near collision of stars imply about 1% will have planets.{{cite journal |title=Protoplanet Migration by Nebula Tides |last1=Ward |first1=W.R. |journal=Icarus |volume=126 |issue=2 |pages=261–281 |date=1997 |url=http://www.gps.caltech.edu/classes/ge133/reading/ward_migration.pdf |publisher=Elsevier |access-date=April 23, 2011 |bibcode=1997Icar..126..261W |doi=10.1006/icar.1996.5647 |archive-date=June 14, 2011 |archive-url=https://web.archive.org/web/20110614091430/http://www.gps.caltech.edu/classes/ge133/reading/ward_migration.pdf |url-status=dead }} Based on extrapolations from the Kepler data, an estimate of around 100 million habitable planets in the Milky Way may be realistic.{{cite web |url=http://www.ted.com/talks/dimitar_sasselov_how_we_found_hundreds_of_earth_like_planets.html |last1=Sasselov |first1=Dimitar |title=How we found hundreds of Earth-like planets |publisher=Ted.com |date=July 2010 |access-date=February 5, 2011 |archive-date=July 27, 2010 |archive-url=https://web.archive.org/web/20100727211015/http://www.ted.com/talks/dimitar_sasselov_how_we_found_hundreds_of_earth_like_planets.html |url-status=dead }} Some media reports of the TED talk have led to the misunderstanding that Kepler had actually found these planets. This was clarified in a letter to the Director of the NASA Ames Research Center, for the Kepler Science Council dated August 2, 2010 states, "Analysis of the current Kepler data does not support the assertion that Kepler has found any Earth-like planets."{{cite journal |last1=Steffen |first1=Jason H. |display-authors=etal |title=Five Kepler target stars that show multiple transiting exoplanet candidates |doi=10.1088/0004-637X/725/1/1226 |pages=1226–1241 |volume=725 |issue=1 |journal=Astrophysical Journal |issn=0004-637X |arxiv=1006.2763 |date=November 9, 2010 |bibcode=2010ApJ...725.1226S|s2cid=14775394 }}{{cite journal |title=Kepler Eclipsing Binary Stars. I. Catalog and Principal Characterization of 1879 Eclipsing Binaries in the First Data Release |arxiv=1006.2815 |first1=Andrej |last1=Prsa |first2=Natalie M. |last2=Batalha |first3=Robert W. |last3=Slawson |first4=Laurance R. |last4=Doyle |first5=William F. |last5=Welsh |first6=Jerome A. |last6=Orosz |first7=Sara |last7=Seager |first8=Michael |last8=Rucker |first9=Kimberly |last9=Mjaseth |first10=Scott G. |last10=Engle |first11=Kyle |last11=Conroy |first12=Jon M. |last12=Jenkins |first13=Douglas A. |last13=Caldwell |first14=David G. |last14=Koch |first15=William J. |last15=Borucki |display-authors=5 |date=January 21, 2011 |doi=10.1088/0004-6256/141/3/83 |volume=141 |issue=3 |journal=The Astronomical Journal |page=83 |bibcode=2011AJ....141...83P|s2cid=13440062 }}

In 2010, Kepler identified two systems containing objects which are smaller and hotter than their parent stars: KOI 74 and KOI 81.{{cite journal |first1=Jason F. |last1=Rowe |first2=William J. |last2=Borucki |first3=David |last3=Koch |first4=Steve B. |last4=Howell |first5=Gibor |last5=Basri |first6=Natalie |last6=Batalha |first7=Timothy M. |last7=Brown |first8=Douglas |last8=Caldwell |first9=William D. |last9=Cochran |first10=Edward |last10=Dunham |first11=Andrea K. |last11=Dupree |first12=Jonathan J. |last12=Fortney |first13=Thomas N. |last13=Gautier III |first14=Ronald L. |last14=Gilliland |first15=Jon |last15=Jenkins |first16=David W. |last16=Latham |first17=Jack J. |last17=Lissauer |first18=Geoff |last18=Marcy |first19=David G. |last19=Monet |first20=Dimitar |last20=Sasselov |first21=William F. |last21=Welsh |display-authors=5 |title=Kepler Observations of Transiting Hot Compact Objects |date=2010 |journal=The Astrophysical Journal Letters |volume=713 |issue=2 |pages=L150–L154 |bibcode=2010ApJ...713L.150R |doi=10.1088/2041-8205/713/2/L150 |arxiv=1001.3420|s2cid=118578253 }} These objects are probably low-mass white dwarfs produced by previous episodes of mass transfer in their systems.

File:Kepler 20 - planet lineup.jpg{{cite web |title=Kepler: A Search For Habitable Planets – Kepler-20e |url=http://kepler.nasa.gov/Mission/discoveries/kepler20e/ |archive-url=https://web.archive.org/web/20120310175648/http://kepler.nasa.gov/Mission/discoveries/kepler20e/ |url-status=dead |archive-date=March 10, 2012 |date=December 20, 2011 |publisher=NASA |access-date=December 23, 2011}} and Kepler-20f{{cite web |title=Kepler: A Search For Habitable Planets – Kepler-20f |url=http://kepler.nasa.gov/Mission/discoveries/kepler20f/ |archive-url=https://web.archive.org/web/20120310195733/http://kepler.nasa.gov/Mission/discoveries/kepler20f/ |url-status=dead |archive-date=March 10, 2012 |date=December 20, 2011 |publisher=NASA |access-date=December 23, 2011}} with Venus and Earth]]

On February 2, 2011, the Kepler team announced the results of analysis of the data taken between 2 May and September 16, 2009.{{cite journal |last1=Borucki |first1=William J. |date=2011 |title=Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data |arxiv=1102.0541 |display-authors=etal |doi=10.1088/0004-637X/736/1/19 |volume=736 |issue=1 |journal=The Astrophysical Journal |page=19 |bibcode=2011ApJ...736...19B|s2cid=15233153 }} They found 1235 planetary candidates circling 997 host stars. (The numbers that follow assume the candidates are really planets, though the official papers called them only candidates. Independent analysis indicated that at least 90% of them are real planets and not false positives).{{cite journal |last1=Morton |first1=Timothy D. |last2=Johnson |first2=John Asher |date=2011 |title=On the Low False Positive Probabilities of Kepler Planet Candidates |journal=The Astrophysical Journal |volume=738 |issue=2 |pages=170 |arxiv=1101.5630|doi=10.1088/0004-637X/738/2/170 |bibcode=2011ApJ...738..170M |s2cid=35223956 }} 68 planets were approximately Earth-size, 288 super-Earth-size, 662 Neptune-size, 165 Jupiter-size, and 19 up to twice the size of Jupiter. In contrast to previous work, roughly 74% of the planets are smaller than Neptune, most likely as a result of previous work finding large planets more easily than smaller ones.

That February 2, 2011 release of 1235 exoplanet candidates included 54 that may be in the "habitable zone", including five less than twice the size of Earth.{{cite web |title=NASA Finds Earth-size Planet Candidates in Habitable Zone, Six Planet System |url=http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=98 |archive-url=https://web.archive.org/web/20110429012133/http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=98 |url-status=dead |archive-date=April 29, 2011 |date=February 2, 2011 |publisher=NASA |access-date=April 24, 2011}}{{Cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=February 2, 2011 |title=Kepler Planet Hunter Finds 1,200 Possibilities |url=https://www.nytimes.com/2011/02/03/science/03planet.html |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20130102083850/https://www.nytimes.com/2011/02/03/science/03planet.html |archive-date=January 2, 2013 |access-date=April 24, 2011 |work=The New York Times }} There were previously only two planets thought to be in the "habitable zone", so these new findings represent an enormous expansion of the potential number of "Goldilocks planets" (planets of the right temperature to support liquid water).{{Cite news |last1=Borenstein |first1=Seth |date=February 2, 2011 |title=NASA spots scores of potentially livable worlds |url=https://www.nbcnews.com/id/wbna41387915 |url-status=live |archive-url=https://web.archive.org/web/20221030074311/https://www.nbcnews.com/id/wbna41387915 |archive-date=October 30, 2022 |access-date=April 24, 2011 |publisher=MSNBC News }} All of the habitable zone candidates found thus far orbit stars significantly smaller and cooler than the Sun (habitable candidates around Sun-like stars will take several additional years to accumulate the three transits required for detection).{{cite web |last1=Alexander |first1=Amir |title=Kepler Discoveries Suggest a Galaxy Rich in Life |publisher=The Planetary Society |date=February 3, 2011 |url=http://www.planetary.org/news/2011/0203_Kepler_Discoveries_Suggest_a_Galaxy.html |access-date=February 4, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110205191952/http://www.planetary.org/news/2011/0203_Kepler_Discoveries_Suggest_a_Galaxy.html |archive-date=February 5, 2011 }} Of all the new planet candidates, 68 are 125% of Earth's size or smaller, or smaller than all previously discovered exoplanets. "Earth-size" and "super-Earth-size" is defined as "less than or equal to 2 Earth radii (Re)" [(or, Rp ≤ 2.0 Re) – Table 5]. Six such planet candidates [namely: KOI 326.01 (Rp=0.85), KOI 701.03 (Rp=1.73), KOI 268.01 (Rp=1.75), KOI 1026.01 (Rp=1.77), KOI 854.01 (Rp=1.91), KOI 70.03 (Rp=1.96) – Table 6] are in the "habitable zone." A more recent study found that one of these candidates (KOI 326.01) is in fact much larger and hotter than first reported.{{cite web |last1=Grant |first1=Andrew |title=Exclusive: "Most Earth-Like" Exoplanet Gets Major Demotion – It Isn't Habitable |url=http://blogs.discovermagazine.com/80beats/2011/03/08/exclusive-most-earth-like-exoplanet-gets-major-demotion%e2%80%94it-isnt-habitable/ |work=Discover Magazine |date=March 8, 2011 |access-date=April 24, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110309132609/http://blogs.discovermagazine.com/80beats/2011/03/08/exclusive-most-earth-like-exoplanet-gets-major-demotion%e2%80%94it-isnt-habitable/ |archive-date=March 9, 2011 }}

The frequency of planet observations was highest for exoplanets two to three times Earth-size, and then declined in inverse proportionality to the area of the planet. The best estimate (as of March 2011), after accounting for observational biases, was: 5.4% of stars host Earth-size candidates, 6.8% host super-Earth-size candidates, 19.3% host Neptune-size candidates, and 2.55% host Jupiter-size or larger candidates. Multi-planet systems are common; 17% of the host stars have multi-candidate systems, and 33.9% of all the planets are in multiple planet systems.{{cite journal |first=William J. |last=Borucki |display-authors=etal |date=2011 |title=Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data |arxiv=1102.0541 |bibcode=2011ApJ...736...19B |doi=10.1088/0004-637X/736/1/19 |journal=The Astrophysical Journal |volume=736 |issue=1 |page=19 |publisher=IOP Publishing |s2cid=15233153 |issn=0004-637X}}

By December 5, 2011, the Kepler team announced that they had discovered 2,326 planetary candidates, of which 207 are similar in size to Earth, 680 are super-Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter. Compared to the February 2011 figures, the number of Earth-size and super-Earth-size planets increased by 200% and 140% respectively. Moreover, 48 planet candidates were found in the habitable zones of surveyed stars, marking a decrease from the February figure; this was due to the more stringent criteria in use in the December data.

On December 20, 2011, the Kepler team announced the discovery of the first Earth-size exoplanets, Kepler-20e and Kepler-20f, orbiting a Sun-like star, Kepler-20.{{cite web |last=Johnson |first=Michele |title=NASA Discovers First Earth-size Planets Beyond Our Solar System |url=http://www.nasa.gov/mission_pages/kepler/news/kepler-20-system.html |publisher=NASA |date=December 20, 2011 |access-date=December 20, 2011 |archive-date=May 16, 2020 |archive-url=https://web.archive.org/web/20200516230313/https://www.nasa.gov/mission_pages/kepler/news/kepler-20-system.html |url-status=dead }}

Based on Kepler's findings, astronomer Seth Shostak estimated in 2011 that "within a thousand light-years of Earth", there are "at least 30,000" habitable planets.{{Cite news |last1=Shostak |first1=Seth |author-link=Seth Shostak |date=February 3, 2011 |title=A Bucketful of Worlds |url=https://www.huffpost.com/entry/a-bucketful-of-worlds_b_817921 |url-status=live |archive-url=https://web.archive.org/web/20240905172202/https://www.huffpost.com/entry/a-bucketful-of-worlds_b_817921 |archive-date=September 5, 2024 |access-date=April 24, 2011 |work=Huffington Post }} Also based on the findings, the Kepler team has estimated that there are "at least 50 billion planets in the Milky Way", of which "at least 500 million" are in the habitable zone.{{cite news |last1=Borenstein |first1=Seth |title=Cosmic census finds crowd of planets in our galaxy |agency=Associated Press |date=February 19, 2011 |url=http://apnews.excite.com/article/20110219/D9LG45NO0.html |access-date=April 24, 2011 |archive-url=https://web.archive.org/web/20110927053134/http://apnews.excite.com/article/20110219/D9LG45NO0.html |archive-date=September 27, 2011 |url-status=dead |df=mdy-all }} In March 2011, astronomers at NASA's Jet Propulsion Laboratory (JPL) reported that about "1.4 to 2.7 percent" of all Sun-like stars are expected to have Earth-size planets "within the habitable zones of their stars". This means there are "two billion" of these "Earth analogs" in the Milky Way alone. The JPL astronomers also noted that there are "50 billion other galaxies", potentially yielding more than one sextillion "Earth analog" planets if all galaxies have similar numbers of planets to the Milky Way.{{Cite news |last1=Choi |first1=Charles Q. |date=March 21, 2011 |title=New Estimate for Alien Earths: 2 Billion in Our Galaxy Alone |url=https://www.space.com/11188-alien-earths-planets-sun-stars.html |url-status=live |archive-url=https://web.archive.org/web/20230322174104/https://www.space.com/11188-alien-earths-planets-sun-stars.html |archive-date=March 22, 2023 |access-date=April 24, 2011 |work=Space.com }}

In January 2012, an international team of astronomers reported that each star in the Milky Way may host "on average...at least 1.6 planets", suggesting that over 160 billion star-bound planets may exist in the Milky Way.{{Cite news |last=Wall |first=Mike |date=January 11, 2012 |title=160 Billion Alien Planets May Exist in Our Milky Way Galaxy |url=https://www.space.com/14200-160-billion-alien-planets-milky-galaxy.html |url-status=live |archive-url=https://web.archive.org/web/20240802113411/https://www.space.com/14200-160-billion-alien-planets-milky-galaxy.html |archive-date=August 2, 2024 |access-date=January 11, 2012 |work=Space.com }}{{cite journal |first1=A. |last1=Cassan |title=One or more bound planets per Milky Way star from microlensing observations |doi=10.1038/nature10684 |date=January 11, 2012 |journal=Nature |volume=481 |pages=167–169 |bibcode=2012Natur.481..167C |pmid=22237108 |issue=7380 |arxiv=1202.0903 |last2=Kubas |first2=D. |last3=Beaulieu |first3=J.-P. |last4=Dominik |first4=M. |last5=Horne |first5=K. |last6=Greenhill |first6=J. |last7=Wambsganss |first7=J. |last8=Menzies |first8=J. |last9=Williams |first9=A. |s2cid=2614136 |display-authors=5 }} Kepler also recorded distant stellar super-flares, some of which are 10,000 times more powerful than the 1859 Carrington event.{{Cite news |last=Amos |first=Jonathan |date=May 17, 2012 |title=Kepler telescope studies star superflares |url=https://www.bbc.com/news/science-environment-18089695 |url-status=live |archive-url=https://web.archive.org/web/20221028091657/https://www.bbc.com/news/science-environment-18089695 |archive-date=October 28, 2022 |access-date=May 31, 2012 |work=BBC News }} The superflares may be triggered by close-orbiting Jupiter-sized planets. The Transit Timing Variation (TTV) technique, which was used to discover Kepler-9d, gained popularity for confirming exoplanet discoveries.[https://web.archive.org/web/20130128110114/http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=226 The Transit Timing Variation (TTV) Planet-finding Technique Begins to Flower]. NASA.gov. A planet in a system with four stars was also confirmed, the first time such a system had been discovered.[https://web.archive.org/web/20130128105815/http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=233 Planet Hunters Find Circumbinary Planet in 4-Star System – 10.16.2012].

{{As of|2012}}, there were a total of 2,321 candidates.{{cite web |url=http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=165 |archive-url=https://web.archive.org/web/20120316051034/http://kepler.nasa.gov/news/nasakeplernews/index.cfm?fuseaction=ShowNews&NewsID=165 |url-status=dead |archive-date=March 16, 2012 |title=Kepler-22b, Super-Earth in the habitable zone of a Sun-like Star |publisher=NASA |date=December 5, 2011}}{{cite web |url=http://news.sciencemag.org/sciencenow/2011/09/super-earth-found-in-habitable-z.html |title='Super-Earth' Found in Habitable Zone |first=Govert |last=Schilling |date=September 12, 2011 |publisher=AAAS |url-status=dead |archive-url=https://web.archive.org/web/20110925020810/http://news.sciencemag.org/sciencenow/2011/09/super-earth-found-in-habitable-z.html |archive-date=September 25, 2011 }}{{cite web |url=http://archive.stsci.edu/kepler/planet_candidates.html |title=Released Kepler Planetary Candidates |publisher=MAST |date=February 27, 2012 |access-date=November 26, 2012}} Of these, 207 are similar in size to Earth, 680 are super-Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter. Moreover, 48 planet candidates were found in the habitable zones of surveyed stars. The Kepler team estimated that 5.4% of all stars host Earth-size planet candidates, and that 17% of all stars have multiple planets.

Image:Exoplanet Period-Mass Scatter Kepler.png

According to a study by Caltech astronomers published in January 2013, the Milky Way contains at least as many planets as it does stars, resulting in 100–400 billion exoplanets.{{cite web |last=Claven |first=Whitney |title=Billions and Billions of Planets |url=http://www.nasa.gov/mission_pages/kepler/news/kepler20130103.html |date=January 3, 2013 |publisher=NASA |access-date=January 3, 2013 |archive-date=April 21, 2020 |archive-url=https://web.archive.org/web/20200421135903/https://www.nasa.gov/mission_pages/kepler/news/kepler20130103.html |url-status=dead }}{{Cite news |date=January 2, 2013 |title=100 Billion Alien Planets Fill Our Milky Way Galaxy: Study |url=https://www.space.com/19103-milky-way-100-billion-planets.html |url-status=live |archive-url=https://web.archive.org/web/20130103060601/http://www.space.com/19103-milky-way-100-billion-planets.html |archive-date=January 3, 2013 |access-date=January 3, 2013 |work=Space.com }} The study, based on planets orbiting the star Kepler-32, suggests that planetary systems may be common around stars in the Milky Way. The discovery of 461 more candidates was announced on January 7, 2013.{{Cite web |url=http://www.nasa.gov/mission_pages/kepler/news/kepler-461-new-candidates.html |title=NASA's Kepler Mission Discovers 461 New Planet Candidates |access-date=January 7, 2013 |archive-date=March 1, 2013 |archive-url=https://web.archive.org/web/20130301094017/http://www.nasa.gov/mission_pages/kepler/news/kepler-461-new-candidates.html |url-status=dead }} The longer Kepler watches, the more planets with long periods it can detect.

{{Cquote|Since the last Kepler catalog was released in February 2012, the number of candidates discovered in the Kepler data has increased by 20 percent and now totals 2,740 potential planets orbiting 2,036 stars|NASA}}

A candidate, newly announced on January 7, 2013, was Kepler-69c (formerly, KOI-172.02), an Earth-size exoplanet orbiting a star similar to the Sun in the habitable zone and possibly habitable.{{Cite news |last=Moskowitz |first=Clara |date=January 9, 2013 |title=Most Earth-Like Alien Planet Possibly Found |url=https://www.space.com/19201-most-earth-like-alien-planet.html |url-status=live |archive-url=https://web.archive.org/web/20240525053811/https://www.space.com/19201-most-earth-like-alien-planet.html |archive-date=May 25, 2024 |access-date=January 9, 2013 |work=Space.com }}

In April 2013, a white dwarf was discovered bending the light of its companion red dwarf in the KOI-256 star system.{{cite news |url=http://www.nasa.gov/mission_pages/kepler/news/kepler20130404.html |title=Gravity-Bending Find Leads to Kepler Meeting Einstein |publisher=NASA |date=April 4, 2013 |access-date=April 6, 2013 |url-status=dead |archive-url=https://web.archive.org/web/20150705131007/http://www.nasa.gov/mission_pages/kepler/news/kepler20130404.html |archive-date=July 5, 2015 }}

In April 2013, NASA announced the discovery of three new Earth-size exoplanets—Kepler-62e, Kepler-62f, and Kepler-69c—in the habitable zones of their respective host stars, Kepler-62 and Kepler-69. The new exoplanets are considered prime candidates for possessing liquid water and thus a habitable environment.{{cite web |last1=Johnson |first1=Michele |last2=Harrington |first2=J.D. |title=NASA's Kepler Discovers Its Smallest 'Habitable Zone' Planets to Date |url=http://www.nasa.gov/mission_pages/kepler/news/kepler-62-kepler-69.html |date=April 18, 2013 |publisher=NASA |access-date=April 18, 2013 |archive-date=May 8, 2020 |archive-url=https://web.archive.org/web/20200508010029/https://www.nasa.gov/mission_pages/kepler/news/kepler-62-kepler-69.html |url-status=dead }}{{Cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=April 18, 2013 |title=2 Good Places to Live, 1,200 Light-Years Away |url=https://www.nytimes.com/2013/04/19/science/space/2-new-planets-are-most-earth-like-yet-scientists-say.html |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20130418183306/http://www.nytimes.com/2013/04/19/science/space/2-new-planets-are-most-earth-like-yet-scientists-say.html |archive-date=April 18, 2013 |access-date=April 18, 2013 |work=The New York Times }}{{cite web |url=https://www.youtube.com/watch?v=P8PJt-R5NxI | archive-url=https://ghostarchive.org/varchive/youtube/20211113/P8PJt-R5NxI| archive-date=2021-11-13 | url-status=live|title=NASA's Kepler Discovers Its Smallest 'Habitable Zone' Planets to Date |publisher=YouTube |date=April 18, 2013 |access-date=April 19, 2013}}{{cbignore}} A more recent analysis has shown that Kepler-69c is likely more analogous to Venus, and thus unlikely to be habitable.{{cite journal |first1=Stephen R. |last1=Kane |first2=Thomas |last2=Barclay |first3=Dawn M. |last3=Gelino |title=A Potential Super-Venus in the Kepler-69 System |publisher=IOP Publishing |issn=2041-8205 |journal=The Astrophysical Journal Letters |arxiv=1305.2933 |date=2013 |bibcode=2013ApJ...770L..20K |volume=770 |page=L20 |doi=10.1088/2041-8205/770/2/L20 |issue=2|s2cid=9808447 }}

On May 15, 2013, NASA announced the space telescope had been crippled by failure of a reaction wheel that keeps it pointed in the right direction. A second wheel had previously failed, and the telescope required three wheels (out of four total) to be operational for the instrument to function properly. Further testing in July and August determined that while Kepler was capable of using its damaged reaction wheels to prevent itself from entering safe mode and of downlinking previously collected science data it was not capable of collecting further science data as previously configured.{{cite web |url=http://www.nasa.gov/content/kepler-mission-manager-update-pointing-test-results |title=Kepler Mission Manager Update: Pointing Test Results |date=August 19, 2013 |publisher=NASA |access-date=September 9, 2013 |archive-date=May 7, 2020 |archive-url=https://web.archive.org/web/20200507172827/https://www.nasa.gov/content/kepler-mission-manager-update-pointing-test-results/ |url-status=dead }} Scientists working on the Kepler project said there was a backlog of data still to be looked at, and that more discoveries would be made in the following couple of years, despite the setback.{{cite news |url=http://www.3news.co.nz/Planet-hunting-Kepler-broken-mission-may-be-over/tabid/1160/articleID/298431/Default.aspx |work=3 News NZ |title=Kepler broken – mission may be over |date=May 20, 2013 |access-date=May 20, 2013 |archive-url=https://web.archive.org/web/20140705045849/http://www.3news.co.nz/Planet-hunting-Kepler-broken-mission-may-be-over/tabid/1160/articleID/298431/Default.aspx |archive-date=July 5, 2014 |url-status=dead }}

Although no new science data from Kepler field had been collected since the problem, an additional sixty-three candidates were announced in July 2013 based on the previously collected observations.{{Cite web |url=http://www.nasa.gov/content/kepler-mission-manager-update-preparing-for-recovery/ |title=NASA – Kepler Mission Manager Update: Preparing for Recovery |access-date=July 16, 2013 |archive-date=August 26, 2020 |archive-url=https://web.archive.org/web/20200826003256/https://www.nasa.gov/content/kepler-mission-manager-update-preparing-for-recovery/ |url-status=dead }}

In November 2013, the second Kepler science conference was held. The discoveries included the median size of planet candidates getting smaller compared to early 2013, preliminary results of the discovery of a few circumbinary planets and planets in the habitable zone.{{cite conference |title=Agenda |conference=Second Kepler Science Conference – NASA Ames Research Center, Mountain View, CA. Nov. 4–8, 2013 |conference-url=http://nexsci.caltech.edu/conferences/KeplerII/agenda.shtml }}

File:ExoplanetDiscoveries-Histogram-20140226.png of exoplanet discoveries. The yellow shaded bar shows newly announced planets including those verified by the multiplicity technique (February 26, 2014).]]

On February 13, over 530 additional planet candidates were announced residing around single planet systems. Several of them were nearly Earth-sized and located in the habitable zone. This number was further increased by about 400 in June 2014.{{cite web |url=http://exoplanetarchive.ipac.caltech.edu/ |title=Welcome to the NASA Exoplanet Archive |publisher=California Institute of Technology |date=February 27, 2014 |access-date=February 27, 2014 |archive-url=https://web.archive.org/web/20140227025004/http://exoplanetarchive.ipac.caltech.edu/ |archive-date=February 27, 2014 |url-status=live |quote=February 13, 2014: The Kepler project has updated dispositions for 534 KOIs in the Q1–Q16 KOI activity table. This brings the total number of Kepler candidates and confirmed planets to 3,841. For more information, see the Purpose of KOI Table document and the interactive tables.}}

On February 26, scientists announced that data from Kepler had confirmed the existence of 715 new exoplanets. A new statistical method of confirmation was used called "verification by multiplicity" which is based on how many planets around multiple stars were found to be real planets. This allowed much quicker confirmation of numerous candidates which are part of multiplanetary systems. 95% of the discovered exoplanets were smaller than Neptune and four, including Kepler-296f, were less than 2 1/2 the size of Earth and were in habitable zones where surface temperatures are suitable for liquid water.{{cite web |last1=Johnson |first1=Michele |last2=Harrington |first2=J.D. |title=NASA's Kepler Mission Announces a Planet Bonanza, 715 New Worlds |url=http://www.nasa.gov/ames/kepler/nasas-kepler-mission-announces-a-planet-bonanza/ |date=February 26, 2014 |publisher=NASA |access-date=February 26, 2014 |archive-date=February 26, 2014 |archive-url=https://web.archive.org/web/20140226202703/http://www.nasa.gov/ames/kepler/nasas-kepler-mission-announces-a-planet-bonanza/ |url-status=dead }}{{Cite news |last=Wall |first=Mike |date=February 26, 2014 |title=Population of Known Alien Planets Nearly Doubles as NASA Discovers 715 New Worlds |url=https://www.space.com/24824-alien-planets-population-doubles-nasa-kepler.html |url-status=live |archive-url=https://web.archive.org/web/20240929021402/https://www.space.com/24824-alien-planets-population-doubles-nasa-kepler.html |archive-date=September 29, 2024 |access-date=February 26, 2014 |work=Space.com }}{{Cite news |last=Amos |first=Jonathan |date=February 26, 2014 |title=Kepler telescope bags huge haul of planets |url=https://www.bbc.com/news/science-environment-26362433 |url-status=live |archive-url=https://web.archive.org/web/20241009110620/https://www.bbc.com/news/science-environment-26362433 |archive-date=October 9, 2024 |access-date=February 27, 2014 |work=BBC News }}{{Cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=February 27, 2014 |title=From Kepler Data, Astronomers Find Galaxy Filled With More but Smaller Worlds |url=https://www.nytimes.com/2014/02/27/science/space/diving-into-kepler-data-astronomers-discover-hundreds-of-planets.html |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20140227020555/http://www.nytimes.com/2014/02/27/science/space/diving-into-kepler-data-astronomers-discover-hundreds-of-planets.html |archive-date=February 27, 2014 |access-date=February 28, 2014 |work=The New York Times }}

In March, a study found that small planets with orbital periods of less than one day are usually accompanied by at least one additional planet with orbital period of 1–50 days. This study also noted that ultra-short period planets are almost always smaller than 2 Earth radii unless it is a misaligned hot Jupiter.{{cite journal |title=A Study of the Shortest-Period Planets Found With Kepler |arxiv=1403.2379 |first1=Roberto |last1=Sanchis-Ojeda |first2=Saul |last2=Rappaport |first3=Joshua N. |last3=Winn |first4=Michael C. |last4=Kotson |first5=Alan M. |last5=Levine |first6=Ileyk |last6=El Mellah |date=March 10, 2014 |doi=10.1088/0004-637X/787/1/47 |volume=787 |issue=1 |journal=The Astrophysical Journal |page=47 |bibcode=2014ApJ...787...47S|s2cid=14380222 }}

On April 17, the Kepler team announced the discovery of Kepler-186f, the first nearly Earth-sized planet located in the habitable zone. This planet orbits around a red dwarf.{{cite web |url=http://www.nasa.gov/ames/kepler/nasas-kepler-discovers-first-earth-size-planet-in-the-habitable-zone-of-another-star/index.html |title=NASA's Kepler Discovers First Earth-Size Planet In The 'Habitable Zone' of Another Star |date=April 17, 2014 |publisher=NASA |access-date=April 26, 2014 |editor=Jessica Culler |others=NASA Official: Brian Dunbar; Image credit(s): 2xNASA Ames/SETI Institute/JPL-Caltech; NASA Ames |first=Jessica |last=Culler |archive-url=https://web.archive.org/web/20140426070848/http://www.nasa.gov/ames/kepler/nasas-kepler-discovers-first-earth-size-planet-in-the-habitable-zone-of-another-star/index.html |archive-date=April 26, 2014 |url-status=live }}

In May 2014, K2 observations fields 0 to 13 were announced and described in detail.{{cite web |last1=Barclay |first1=Thomas |last2=Dotson |first2=Jessie |title=K2 Campaign Fields – 0 to 13 |url=http://keplerscience.arc.nasa.gov/K2/Fields.shtml |archive-url=https://web.archive.org/web/20140426094927/http://keplerscience.arc.nasa.gov/K2/Fields.shtml |url-status=dead |archive-date=April 26, 2014 |date=May 29, 2014 |publisher=NASA |access-date=April 4, 2015}} K2 observations began in June 2014.

In July 2014, the first discoveries from K2 field data were reported in the form of eclipsing binaries. Discoveries were derived from a Kepler engineering data set which was collected prior to campaign 0{{cite web |last1=Barclay |first1=Thomas |last2=Dotson |first2=Jessie |title=K2 Campaign 0 (March 8, 2014 – May 30, 2014) |url=http://keplerscience.arc.nasa.gov/K2/GuestInvestigationsC00.shtml |archive-url=https://web.archive.org/web/20140801130152/http://keplerscience.arc.nasa.gov/K2/GuestInvestigationsC00.shtml |url-status=dead |archive-date=August 1, 2014 |date=May 29, 2014 |publisher=NASA |access-date=April 4, 2015}} in preparation to the main K2 mission.{{cite journal |title=Kepler Eclipsing Binary Stars. V. Identification of 31 Candidate Eclipsing Binaries in the K2 Engineering Dataset |journal=Publications of the Astronomical Society of the Pacific |first1=Kyle E. |last1=Conroy |first2=Andrej |last2=Prša |first3=Keivan G. |last3=Stassun |first4=Steven |last4=Bloemen |first5=Mahmoud |last5=Parvizi |first6=Billy |last6=Quarles |first7=Tabetha |last7=Boyajian |first8=Thomas |last8=Barclay |first9=Avi |last9=Shporer |first10=David W. |last10=Latham |first11=Michael |last11=Abdul-Masih |display-authors=5 |volume=126 |issue=944 |pages=914–922 |date=October 2014 |doi=10.1086/678953 |bibcode=2014PASP..126..914C |arxiv=1407.3780|s2cid=8232628 }}

On September 23, 2014, NASA reported that the K2 mission had completed campaign 1,{{cite web |last1=Barclay |first1=Thomas |last2=Dotson |first2=Jessie |title=K2 Campaign 1 (May 30, 2014 – August 21, 2014) |url=http://keplerscience.arc.nasa.gov/K2/GuestInvestigationsC01.shtml |archive-url=https://web.archive.org/web/20140801104443/http://keplerscience.arc.nasa.gov/K2/GuestInvestigationsC01.shtml |url-status=dead |archive-date=August 1, 2014 |date=May 29, 2014 |publisher=NASA |access-date=April 4, 2015}} the first official set of science observations, and that campaign 2{{cite web |last1=Barclay |first1=Thomas |last2=Dotson |first2=Jessie |title=K2 Campaign 2 (August 22, 2014 – November 11, 2014) |url=http://keplerscience.arc.nasa.gov/K2/GuestInvestigationsC02.shtml |archive-url=https://web.archive.org/web/20141105054749/http://keplerscience.arc.nasa.gov/K2/GuestInvestigationsC02.shtml |url-status=dead |archive-date=November 5, 2014 |date=May 29, 2014 |publisher=NASA |access-date=April 4, 2015}} was underway.{{cite web |last=Sobeck |first=Charlie |title=Mission Manager Update: C1 data on the ground; C2 underway |url=http://www.nasa.gov/ames/kepler/mission-manager-update-c1-data-on-the-ground-c2-underway |date=September 23, 2014 |publisher=NASA |access-date=September 23, 2014 |archive-date=April 17, 2018 |archive-url=https://web.archive.org/web/20180417220541/https://www.nasa.gov/ames/kepler/mission-manager-update-c1-data-on-the-ground-c2-underway/ |url-status=dead }}

File:KeplerSpaceTelescope-SupernovaKSN2011b-20150520.png, in the process of exploding: before, during and after.]]

Campaign 3{{cite web |last1=Barclay |first1=Thomas |last2=Dotson |first2=Jessie |title=K2 Campaign 3 (November 14, 2014 – February 6, 2014) |url=http://keplerscience.arc.nasa.gov/K2/GuestInvestigationsC03.shtml |archive-url=https://web.archive.org/web/20150102121432/http://keplerscience.arc.nasa.gov/K2/GuestInvestigationsC03.shtml |url-status=dead |archive-date=January 2, 2015 |date=May 29, 2014 |publisher=NASA |access-date=April 4, 2015}} lasted from November 14, 2014, to February 6, 2015, and included "16,375 standard long cadence and 55 standard short cadence targets".

{{prose|section|date=March 2023}}

• In January 2015, the number of confirmed Kepler planets exceeded 1000. At least two (Kepler-438b and Kepler-442b) of the discovered planets announced that month were likely rocky and in the habitable zone. Also in January 2015, NASA reported that five confirmed sub-earth-sized rocky exoplanets, all smaller than the planet Venus, were found orbiting the 11.2 billion year old star Kepler-444, making this star system, at 80% of the age of the universe, the oldest yet discovered.{{cite journal |title=An Ancient Extrasolar System with Five Sub-Earth-size Planets |journal=The Astrophysical Journal |first1=T. L. |last1=Campante |first2=T. |last2=Barclay |first3=J. J. |last3=Swift |first4=D. |last4=Huber |first5=V. Zh. |last5=Adibekyan |first6=W. |last6=Cochran |first7=C. J. |last7=Burke |first8=H. |last8=Isaacson |first9=E. V. |last9=Quintana |first10=G. R. |last10=Davies |first11=V. |last11=Silva Aguirre |first12=D. |last12=Ragozzine |first13=R. |last13=Riddle |first14=C. |last14=Baranec |first15=S. |last15=Basu |first16=W. J. |last16=Chaplin |first17=J. |last17=Christensen-Dalsgaard |first18=T. S. |last18=Metcalfe |first19=T. R. |last19=Bedding |first20=R. |last20=Handberg |first21=D. |last21=Stello |first22=J. M. |last22=Brewer |first23=S. |last23=Hekker |first24=C. |last24=Karoff |first25=R. |last25=Kolbl |first26=N. M. |last26=Law |first27=M. |last27=Lundkvist |first28=A. |last28=Miglio |first29=J. F. |last29=Rowe |first30=N. C. |last30=Santos |first31=C. |last31=Van Laerhoven |first32=T. |last32=Arentoft |first33=Y. P. |last33=Elsworth |first34=D. A. |last34=Fischer |first35=S. D. |last35=Kawaler |first36=H. |last36=Kjeldsen |first37=M. N. |last37=Lund |first38=G. W. |last38=Marcy |first39=S. G. |last39=Sousa |first40=A. |last40=Sozzetti |first41=T. R. |last41=White |display-authors=5 |volume=799 |issue=2 |at=article 170 |date=February 2015 |doi=10.1088/0004-637X/799/2/170 |bibcode=2015ApJ...799..170C |arxiv=1501.06227|s2cid=5404044 }}{{Cite news |last=Dunn |first=Marcia |date=January 27, 2015 |title=Astronomers find solar system more than double ours in age |url=https://apnews.com/general-news-1b42cd9c22fa48a6b57fcbe1dccbd617 |url-status=live |archive-url=https://web.archive.org/web/20240107030243/https://apnews.com/general-news-1b42cd9c22fa48a6b57fcbe1dccbd617 |archive-date=January 7, 2024 |access-date=January 27, 2015 |work=Associated Press }}{{Cite news |last1=Atkinson |first1=Nancy |date=January 27, 2015 |title=Oldest Planetary System Discovered, Improving the Chances for Intelligent Life Everywhere |url=https://www.universetoday.com/118510/oldest-planetary-system-discovered-improving-the-chances-for-intelligent-life-everywhere/ |url-status=live |archive-url=https://web.archive.org/web/20240424155023/https://www.universetoday.com/118510/oldest-planetary-system-discovered-improving-the-chances-for-intelligent-life-everywhere/ |archive-date=April 24, 2024 |access-date=January 27, 2015 |work=Universe Today }}
• In April 2015, campaign 4{{cite web |url=http://keplerscience.arc.nasa.gov/K2/GuestInvestigationsC04.shtml |archive-url=https://web.archive.org/web/20150224214845/http://keplerscience.arc.nasa.gov/K2/GuestInvestigationsC04.shtml |url-status=dead |archive-date=February 24, 2015 |title=K2 Campaign 4 (February 7, 2015 – April 24, 2015) |publisher=NASA |last1=Barclay |first1=Thomas |last2=Dotson |first2=Jessie |date=May 29, 2014 |access-date=April 4, 2015}} was reported to last between February 7, 2015, and April 24, 2015, and to include observations of nearly 16,000 target stars and two notable open star clusters, Pleiades and Hyades.{{cite web |url=http://www.nasa.gov/ames/kepler/mission-manager-update-k2-in-campaign-4/ |title=Mission Manager Update: K2 in Campaign 4 |publisher=NASA |last1=Sobeck |first1=Charlie |last2=Johnson |first2=Michele |last3=Dunbar |first3=Brian |date=April 2, 2015 |access-date=April 4, 2015 |archive-date=September 23, 2020 |archive-url=https://web.archive.org/web/20200923135725/https://www.nasa.gov/ames/kepler/mission-manager-update-k2-in-campaign-4/ |url-status=dead }}
• In May 2015, Kepler observed a newly discovered supernova, KSN 2011b (Type 1a), before, during and after explosion. Details of the pre-nova moments may help scientists better understand dark energy.{{cite web |url=http://www.nasa.gov/ames/kepler/nasa-spacecraft-capture-rare-early-moments-of-baby-supernovae |title=NASA Spacecraft Capture Rare, Early Moments of Baby Supernovae |publisher=NASA |last1=Johnson |first1=Michele |last2=Chandler |first2=Lynn |date=May 20, 2015 |access-date=May 21, 2015 |archive-date=November 8, 2020 |archive-url=https://web.archive.org/web/20201108105310/http://www.nasa.gov/ames/kepler/nasa-spacecraft-capture-rare-early-moments-of-baby-supernovae/ |url-status=dead }}
• On July 24, 2015, NASA announced the discovery of Kepler-452b, a confirmed exoplanet that is near-Earth in size and found orbiting the habitable zone of a Sun-like star.{{Cite press release |last1=Chou |first1=Felicia |last2=Johnson |first2=Michele |date=July 23, 2015 |title=NASA's Kepler Mission Discovers Bigger, Older Cousin to Earth |url=https://www.nasa.gov/news-release/nasas-kepler-mission-discovers-bigger-older-cousin-to-earth/ |url-status=live |archive-url=https://web.archive.org/web/20241007083734/https://www.nasa.gov/news-release/nasas-kepler-mission-discovers-bigger-older-cousin-to-earth/ |archive-date=October 7, 2024 |access-date=July 23, 2015 |publisher=NASA |id=15-156 }}{{cite journal |title=Discovery and Validation of Kepler-452b: A 1.6 R⨁ Super Earth Exoplanet in the Habitable Zone of a G2 Star |journal=The Astronomical Journal |last1=Jenkins |first1=Jon M. |last2=Twicken |first2=Joseph D. |last3=Batalha |first3=Natalie M. |last4=Caldwell |first4=Douglas A. |last5=Cochran |first5=William D. |last6=Endl |first6=Michael |last7=Latham |first7=David W. |last8=Esquerdo |first8=Gilbert A. |last9=Seader |first9=Shawn|last10=Bieryla|first10=Allyson |last11=Petigura |first11=Erik |last12=Ciardi |first12=David R. |last13=Marcy |first13=Geoffrey W. |last14=Isaacson |first14=Howard |last15=Huber |first15=Daniel |last16=Rowe |first16=Jason F. |last17=Torres |first17=Guillermo |last18=Bryson |first18=Stephen T. |last19=Buchhave |first19=Lars |last20=Ramirez |first20=Ivan |last21=Wolfgang |first21=Angie |last22=Li |first22=Jie |last23=Campbell |first23=Jennifer R. |last24=Tenenbaum |first24=Peter |last25=Sanderfer |first25=Dwight |last26=Henze |first26=Christopher E. |last27=Catanzarite |first27=Joseph H. |last28=Gilliland |first28=Ronald L. |last29=Borucki |first29=William J. |display-authors=5 |volume=150 |issue=2 |page=56 |date=July 2015 |doi=10.1088/0004-6256/150/2/56 |bibcode=2015AJ....150...56J |arxiv=1507.06723|s2cid=26447864 }} The seventh Kepler planet candidate catalog was released, containing 4,696 candidates, and increase of 521 candidates since the previous catalog release in January 2015.{{Cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=July 23, 2015 |title=NASA Says Data Reveals an Earth-Like Planet, Kepler 452b |url=https://www.nytimes.com/2015/07/24/science/space/kepler-data-reveals-what-might-be-best-goldilocks-planet-yet.html |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20150724153629/http://www.nytimes.com/2015/07/24/science/space/kepler-data-reveals-what-might-be-best-goldilocks-planet-yet.html |archive-date=July 24, 2015 |access-date=July 24, 2015 |work=The New York Times }}{{Cite web |last=Johnson |first=Michele |date=July 23, 2015 |title=Kepler Planet Candidates, July 2015 |url=https://www.nasa.gov/image-article/kepler-planet-candidates-july-2015/ |url-status=live |archive-url=https://web.archive.org/web/20240315093840/https://www.nasa.gov/image-article/kepler-planet-candidates-july-2015/ |archive-date=March 15, 2024 |access-date=July 24, 2015 |publisher=NASA }}
• On September 14, 2015, astronomers reported unusual light fluctuations of KIC 8462852, an F-type main-sequence star in the constellation Cygnus, as detected by Kepler, while searching for exoplanets. Various hypotheses have been presented, including comets, asteroids, and an alien civilization.{{Cite news |last=Kaplan |first=Sarah |date=October 15, 2015 |title=The strange star that has serious scientists talking about an alien megastructure |url=https://www.washingtonpost.com/news/morning-mix/wp/2015/10/15/the-strange-star-that-has-serious-scientists-talking-about-an-alien-megastructure/ |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20151017095720/https://www.washingtonpost.com/news/morning-mix/wp/2015/10/15/the-strange-star-that-has-serious-scientists-talking-about-an-alien-megastructure/ |archive-date=October 17, 2015 |access-date=October 15, 2015 |issn=0190-8286 |newspaper=The Washington Post }}{{Cite magazine |last1=Andersen |first1=Ross |date=October 13, 2015 |title=The Most Mysterious Star in Our Galaxy |url=https://www.theatlantic.com/science/archive/2015/10/the-most-interesting-star-in-our-galaxy/410023/ |url-status=live |archive-url=https://web.archive.org/web/20241002103300/https://www.theatlantic.com/science/archive/2015/10/the-most-interesting-star-in-our-galaxy/410023/ |archive-date=October 2, 2024 |access-date=October 13, 2015 |magazine=The Atlantic |issn=1072-7825 |eissn=2151-9463 }}{{cite journal |title=Planet Hunters IX. KIC 8462852 – Where's the flux? |journal=Monthly Notices of the Royal Astronomical Society |last1=Boyajian |first1=T. S. |last2=LaCourse |first2=D. M. |last3=Rappaport |first3=S. A. |last4=Fabrycky |first4=D. |last5=Fischer |first5=D. A. |last6=Gandolfi |first6=D. |last7=Kennedy |first7=G. M. |last8=Liu |first8=M. C. |last9=Moor |first9=A. |last10=Olah |first10=K. |last11=Vida |first11=K. |last12=Wyatt |first12=M. C. |last13=Best |first13=W. M. J. |last14=Ciesla |first14=F. |last15=Csak |first15=B. |last16=Dupuy |first16=T. J. |last17=Handler |first17=G. |last18=Heng |first18=K. |last19=Korhonen |first19=H. |last20=Kovacs |first20=J. |last21=Kozakis |first21=T. |last22=Kriskovics |first22=L. |last23=Schmitt |first23=J. R. |last24=Szabo |first24=Gy. |last25=Szabo |first25=R. |last26=Wang |first26=J. |last27=Goodman |first27=S. |last28=Hoekstra |first28=A. |last29=Jek |first29=K. J. |display-authors=5 |volume=457 |issue=4 |pages=3988–4004 |date=April 2016 |doi=10.1093/mnras/stw218 |doi-access=free |bibcode=2016MNRAS.457.3988B |arxiv=1509.03622|s2cid=54859232 }}

By May 10, 2016, the Kepler mission had verified 1,284 new planets. Based on their size, about 550 could be rocky planets. Nine of these orbit in their stars' habitable zone: Kepler-560b, Kepler-705b, Kepler-1229b, Kepler-1410b, Kepler-1455b, Kepler-1544 b, Kepler-1593b, Kepler-1606b, and Kepler-1638b.

The Kepler team originally promised to release data within one year of observations.{{cite web |url=http://kepler.nasa.gov/Mission/faq/#a9 |archive-url=https://web.archive.org/web/20100527093519/http://kepler.nasa.gov/Mission/faq/#a9 |url-status=dead |archive-date=May 27, 2010 |title=Frequently Asked Questions from the Public |access-date=September 6, 2011 |quote=Data for each 3-month observation period will be made public within one year of the end the observation period.}} However, this plan was changed after launch, with data being scheduled for release up to three years after its collection.{{cite web |title=NASA's Kepler Mission Data Release Schedule |url=http://keplergo.arc.nasa.gov/ArchiveSchedule.shtml |archive-url=https://web.archive.org/web/20091016015816/http://keplergo.arc.nasa.gov/ArchiveSchedule.shtml |url-status=dead |archive-date=October 16, 2009 |publisher=NASA |access-date=October 18, 2011}} On this schedule, the data from the quarter ending June 2010 was scheduled to be released in June 2013. This resulted in considerable criticism,{{Cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=June 14, 2010 |title=In the Hunt for Planets, Who Owns the Data? |url=https://www.nytimes.com/2010/06/15/science/space/15kepler.html |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20100617074946/http://www.nytimes.com/2010/06/15/science/space/15kepler.html |archive-date=June 17, 2010 |work=The New York Times }}{{Cite journal |last=Hand |first=Eric |date=April 14, 2010 |title=Telescope team may be allowed to sit on exoplanet data |url=http://www.nature.com/news/2010/100414/full/news.2010.182.html |url-status=live |journal=Nature |doi=10.1038/news.2010.182 |issn=0028-0836 |eissn=1476-4687 |archive-url=https://web.archive.org/web/20100416011151/http://www.nature.com/news/2010/100414/full/news.2010.182.html |archive-date=April 16, 2010 }}{{Cite magazine |last=MacRobert |first=Alan |date=May 26, 2011 |title=Kepler's Exoplanets: A Progress Report |url=https://skyandtelescope.org/astronomy-news/keplers-exoplanets-aprogress-report/ |url-status=live |archive-url=https://web.archive.org/web/20231011101913/https://skyandtelescope.org/astronomy-news/keplers-exoplanets-aprogress-report/ |archive-date=October 11, 2023 |magazine=Sky & Telescope }}{{cite web |title=Minutes of the Kepler Users Panel |url=http://keplergo.arc.nasa.gov/docs/KUP_minutes_Mar2011.pdf |archive-url=https://web.archive.org/web/20111015194243/http://keplergo.arc.nasa.gov/docs/KUP_minutes_Mar2011.pdf |url-status=dead |archive-date=October 15, 2011 |date=March 28–29, 2011 |first=Alex |last=Brown}}{{cite web |url=http://news.discovery.com/space/kepler-exoplanet-controversy-erupts.html |title=Kepler Exoplanet Controversy Erupts |first=Nicole |last=Gugliucci |date=June 15, 2010 |publisher=Discovery News |access-date=October 4, 2011 |archive-date=November 12, 2012 |archive-url=https://web.archive.org/web/20121112182620/http://news.discovery.com/space/kepler-exoplanet-controversy-erupts.html |url-status=dead }} leading the Kepler science team to release the third quarter of their data one year and nine months after collection.{{cite web |url=http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=145 |archive-url=https://web.archive.org/web/20111019083528/http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=145 |url-status=dead |archive-date=October 19, 2011 |title=NASA's Kepler Mission Announces Next Data Release to Public Archive|date=March 31, 2015}} The data through September 2010 (quarters 4, 5, and 6) was made public in January 2012.{{cite web |url=http://keplergo.arc.nasa.gov/ArchiveSchedule.shtml |archive-url=https://web.archive.org/web/20091016015816/http://keplergo.arc.nasa.gov/ArchiveSchedule.shtml |url-status=dead |archive-date=October 16, 2009 |title=Kepler Data Collection and Archive Timeline |access-date=January 1, 2012}}

Periodically, the Kepler team releases a list of candidates (Kepler Objects of Interest, or KOIs) to the public. Using this information, a team of astronomers collected radial velocity data using the SOPHIE échelle spectrograph to confirm the existence of the candidate KOI-428b in 2010, later named Kepler-40b.{{cite journal |title=SOPHIE velocimetry of Kepler transit candidates. II. KOI-428b: A hot Jupiter transiting a subgiant F-star |journal=Astronomy & Astrophysics |first1=A. |last1=Santerne |first2=R. F. |last2=Diaz |first3=F. |last3=Bouchy |first4=M. |last4=Deleuil |first5=C. |last5=Moutou |first6=G. |last6=Hebrard |first7=A. |last7=Eggenberger |first8=D. |last8=Ehrenreich |first9=C. |last9=Gry |first10=S. |last10=Udry |display-authors=5 |volume=528 |at=A63 |date=April 2011 |doi=10.1051/0004-6361/201015764 |bibcode=2011A&A...528A..63S |arxiv=1101.0196|s2cid=119275985 }} In 2011, the same team confirmed candidate KOI-423b, later named Kepler-39b.{{Cite journal |title=SOPHIE velocimetry of Kepler transit candidates. III. KOI-423b: an 18 M_Jup transiting companion around an F7IV star |journal=Astronomy & Astrophysics |first1=F. |last1=Bouchy |first2=A. S. |last2=Bonomo |first3=A. |last3=Santerne |first4=C. |last4=Moutou |first5=M. |last5=Deleuil |first6=R. F. |last6=Díaz |first7=A. |last7=Eggenberger |first8=D. |last8=Ehrenreich |first9=C. |last9=Gry |first10=T. |last10=Guillot |first11=M. |last11=Havel |first12=G. |last12=Hébrard |first13=S. |last13=Udry |display-authors=5 |volume=533 |at=A83 |date=September 2011 |doi=10.1051/0004-6361/201117095 |bibcode=2011A&A...533A..83B |arxiv=1106.3225|s2cid=62836749 }}

Since December 2010, Kepler mission data has been used for the Planet Hunters project, which allows volunteers to look for transit events in the light curves of Kepler images to identify planets that computer algorithms might miss.{{Cite magazine |last1=Andrews |first1=Bill |date=December 20, 2010 |title=Become a Planet Hunter! |url=https://cs.astronomy.com/asy/b/astronomy/archive/2010/12/20/become-a-planet-hunter.aspx |url-status=live |archive-url=https://web.archive.org/web/20220126230506/https://cs.astronomy.com/asy/b/astronomy/archive/2010/12/20/become-a-planet-hunter.aspx |archive-date=January 26, 2022 |access-date=April 24, 2011 |magazine=Astronomy }} By June 2011, users had found sixty-nine potential candidates that were previously unrecognized by the Kepler mission team.{{cite web |title=Planetometer |url=http://www.planethunters.org/planetometer |publisher=Zooniverse |access-date=June 15, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110721124511/http://www.planethunters.org/planetometer |archive-date=July 21, 2011 }} The team has plans to publicly credit amateurs who spot such planets.

In January 2012, the BBC program Stargazing Live aired a public appeal for volunteers to analyse Planethunters.org data for potential new exoplanets. This led two amateur astronomers—one in Peterborough, England—to discover a new Neptune-sized exoplanet, to be named Threapleton Holmes B.{{cite news |url=https://www.telegraph.co.uk/news/science/space/9026837/Amateur-stargazers-discover-new-planet.html |archive-url=https://ghostarchive.org/archive/20220112/https://www.telegraph.co.uk/news/science/space/9026837/Amateur-stargazers-discover-new-planet.html |archive-date=January 12, 2022 |url-access=subscription |url-status=live |work=The Daily Telegraph |title=Amateur stargazers discover new planet |date=January 20, 2012 |access-date=January 20, 2012}}{{cbignore}} One hundred thousand other volunteers were also engaged in the search by late January, analyzing over one million Kepler images by early 2012.{{Cite news |last=Amos |first=Jonathan |date=January 18, 2012 |title=Stargazing viewer in planet coup |url=https://www.bbc.co.uk/news/science-environment-16612181 |url-status=live |archive-url=https://web.archive.org/web/20240912185727/https://www.bbc.com/news/science-environment-16612181 |archive-date=September 12, 2024 |access-date=January 19, 2012 |work=BBC News }} One such exoplanet, PH1b (or Kepler-64b from its Kepler designation), was discovered in 2012. A second exoplanet, PH2b (Kepler-86b) was discovered in 2013.

In April 2017, ABC Stargazing Live, a variation of BBC Stargazing Live, launched the Zooniverse project "Exoplanet Explorers". While Planethunters.org worked with archived data, Exoplanet Explorers used recently downlinked data from the K2 mission. On the first day of the project, 184 transit candidates were identified that passed simple tests. On the second day, the research team identified a star system, later named K2-138, with a Sun-like star and four super-Earths in a tight orbit. In the end, volunteers helped to identify 90 exoplanet candidates.{{cite web |url=https://www.zooniverse.org/projects/ianc2/exoplanet-explorers/about/results |title=We Got One!!! |series=Exoplanet Explorers |work=Zooniverse.org |access-date=April 18, 2017}}{{Cite web |date=April 7, 2017 |title=Stargazing Live 2017: Thank you all! |url=https://blog.zooniverse.org/2017/04/07/stargazing-live-2017-thank-you-all/ |url-status=live |archive-url=https://web.archive.org/web/20240616182121/https://blog.zooniverse.org/2017/04/07/stargazing-live-2017-thank-you-all/ |archive-date=June 16, 2024 |access-date=April 18, 2017 |website=Zooniverse.org }} The citizen scientists that helped discover the new star system will be added as co-authors in the research paper when published.{{Cite news |last=Miller |first=Daniel |date=April 6, 2017 |title=Stargazing Live viewers find four-planet solar system via crowd-sourcing project |url=https://www.abc.net.au/news/2017-04-06/stargazing-live-four-planets-discovered-in-new-solar-system/8423142 |url-status=live |archive-url=https://web.archive.org/web/20240725051056/https://www.abc.net.au/news/2017-04-06/stargazing-live-four-planets-discovered-in-new-solar-system/8423142 |archive-date=July 25, 2024 |access-date=April 18, 2017 |work=ABC }}

{{main|List of exoplanets discovered by the Kepler space telescope}}

{{main|List of planets observed during Kepler's K2 mission}}

{{see also|List of exoplanetary host stars|List of exoplanets}}

File:KeplerExoplanets-NearEarthSize-HabitableZone-20150106.pngs (Kepler-62e, Kepler-62f, Kepler-186f, Kepler-296e, Kepler-296f, Kepler-438b, Kepler-440b, Kepler-442b).]]

Exoplanets discovered using Kepler{{'s}} data, but confirmed by outside researchers, include Kepler-39b, Kepler-40b, Kepler-41b,{{cite encyclopedia |first=Cyril |last=Dedieu |url=http://exoplanet.eu/star.php?st=KOI-196 |title=Star: KOI-196 |access-date=December 21, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20120111063437/http://exoplanet.eu/star.php?st=KOI-196 |encyclopedia=Extrasolar Planets Encyclopaedia |archive-date=January 11, 2012 }} Kepler-43b,{{cite encyclopedia |url=http://exoplanet.eu/star.php?st=KOI-135 |title=Star: KOI-135 |access-date=December 21, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20120101111049/http://exoplanet.eu/star.php?st=KOI-135 |encyclopedia=Extrasolar Planets Encyclopaedia |archive-date=January 1, 2012 }} Kepler-44b,{{cite encyclopedia |url=http://exoplanet.eu/star.php?st=KOI-204 |title=Star: KOI-204 |access-date=December 21, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20120101104353/http://exoplanet.eu/star.php?st=KOI-204 |encyclopedia=Extrasolar Planets Encyclopaedia |archive-date=January 1, 2012 }} Kepler-45b,{{cite encyclopedia |url=http://exoplanet.eu/star.php?st=KOI-254 |title=Star: KOI-254 |access-date=December 21, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20120119195842/http://exoplanet.eu/star.php?st=KOI-254 |encyclopedia=Extrasolar Planets Encyclopaedia |archive-date=January 19, 2012 }} as well as the planets orbiting Kepler-223{{cite encyclopedia |url=http://exoplanet.eu/star.php?st=KOI-730 |title=Star: KOI-730 |access-date=December 21, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20120616124736/http://exoplanet.eu/star.php?st=KOI-730 |encyclopedia=Extrasolar Planets Encyclopaedia |archive-date=June 16, 2012 }} and Kepler-42.{{cite encyclopedia |url=http://exoplanet.eu/star.php?st=KOI-961 |archive-url=https://web.archive.org/web/20120208054043/http://exoplanet.eu/star.php?st=KOI-961 |url-status=dead |archive-date=February 8, 2012 |encyclopedia=Extrasolar Planets Encyclopaedia |title=Star: KOI-961 |access-date=January 1, 2012}} The "KOI" acronym indicates that the star is a Kepler Object of Interest.

{{Main|Kepler Input Catalog}}

The Kepler Input Catalog is a publicly searchable database of roughly 13.2 million targets used for the Kepler Spectral Classification Program and the Kepler mission.{{cite web |url=http://archive.stsci.edu/kepler/kic10/help/search_help.html |title=MAST KIC Search Help |publisher=Space Telescope Science Institute |access-date=April 23, 2011}}{{cite web |url=http://archive.stsci.edu/kepler/kic10/search.php |title=KIC10 Search |access-date=April 23, 2011}} The catalog alone is not used for finding Kepler targets, because only a portion of the listed stars (about one-third of the catalog) can be observed by the spacecraft.

Kepler has been assigned an observatory code {{Obscode|C55}} in order to report its astrometric observations of small Solar System bodies to the Minor Planet Center. In 2013 the alternative NEOKepler mission was proposed, a search for near-Earth objects, in particular potentially hazardous asteroids (PHAs). Its unique orbit and larger field of view than existing survey telescopes allow it to look for objects inside Earth's orbit. It was predicted a 12-month survey could make a significant contribution to the hunt for PHAs as well as potentially locating targets for NASA's Asteroid Redirect Mission.{{cite arXiv |title=NEOKepler: Discovering Near-Earth Objects Using the Kepler Spacecraft |eprint=1309.1096 |class=astro-ph.EP |first1=Kevin B. |last1=Stevenson |first2=Daniel |last2=Fabrycky |first3=Robert |last3=Jedicke |first4=William |last4=Bottke |first5=Larry |last5=Denneau |date=September 2013}} Kepler's first discovery in the Solar System, however, was {{LoMP|506121|{{mp|506121|2016 BP|81}}}}, a 200-kilometer cold classical Kuiper belt object located beyond the orbit of Neptune.{{Cite web |title=506121 (2016 BP81) |url=https://www.minorplanetcenter.net/db_search/show_object?object_id=506121 |url-status=live |archive-url=https://web.archive.org/web/20171222220142/https://minorplanetcenter.net/db_search/show_object?object_id=506121 |archive-date=December 22, 2017 |access-date=March 28, 2018 |website=Minor Planet Center }}

File:KeplerSpaceTelescope -Retirement-ArtistConcept-20181030.jpg

On October 30, 2018, NASA announced that the Kepler space telescope, having run out of fuel, and after nine years of service and the discovery of over 2,600 exoplanets, has been officially retired, and will maintain its current, safe orbit, away from Earth.{{Cite press release |last1=Chou |first1=Felicia |last2=Hawkes |first2=Alison |last3=Cofield |first3=Calia |date=October 30, 2018 |title=NASA Retires Kepler Space Telescope |url=https://www.jpl.nasa.gov/news/nasa-retires-kepler-space-telescope/ |url-status=live |archive-url=https://web.archive.org/web/20240910121233/https://www.jpl.nasa.gov/news/nasa-retires-kepler-space-telescope |archive-date=September 10, 2024 |access-date=October 30, 2018 |publisher=NASA / JPL |id=2018-254 }}{{Cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=October 30, 2018 |title=Kepler, the Little NASA Spacecraft That Could, No Longer Can |url=https://www.nytimes.com/2018/10/30/science/nasa-kepler-exoplanet.html |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20181030211627/https://www.nytimes.com/2018/10/30/science/nasa-kepler-exoplanet.html |archive-date=October 30, 2018 |access-date=October 30, 2018 |work=The New York Times }} The spacecraft was deactivated with a "goodnight" command sent from the mission's control center at the Laboratory for Atmospheric and Space Physics on November 15, 2018.{{Cite news |last=Wall |first=Mike |date=November 16, 2018 |title=Farewell, Kepler: NASA Shuts Down Prolific Planet-Hunting Space Telescope |url=https://www.space.com/42461-kepler-exoplanet-hunting-telescope-shuts-down.html |url-status=live |archive-url=https://web.archive.org/web/20181116223512/https://www.space.com/42461-kepler-exoplanet-hunting-telescope-shuts-down.html |archive-date=November 16, 2018 |access-date=November 16, 2018 |work=Space.com |quote=NASA decommissioned the Kepler space telescope last night (Nov. 15), beaming "goodnight" commands to the sun-orbiting observatory. [...] The final commands were sent from Kepler's operations center at the University of Colorado Boulder's Laboratory for Atmospheric and Space Physics... }} Kepler's retirement coincides with the 388th anniversary of Johannes Kepler's death in 1630.{{Cite press release |last1=Chou |first1=Felicia |last2=Hawkes |first2=Alison |last3=Cofield |first3=Calla |date=November 16, 2018 |title=Kepler Telescope Bids 'Goodnight' with Final Commands |url=https://www.jpl.nasa.gov/news/kepler-telescope-bids-goodnight-with-final-commands/ |url-status=live |archive-url=https://web.archive.org/web/20240419080338/https://www.jpl.nasa.gov/news/kepler-telescope-bids-goodnight-with-final-commands |archive-date=April 19, 2024 |access-date=November 16, 2018 |publisher=NASA / JPL |id=208-266 |quote=Coincidentally, Kepler's "goodnight" falls on the same date as the 388-year anniversary of the death of its namesake, German astronomer Johannes Kepler... }}

{{div col|colwidth=36em}}

• Kepler-22b, the first exoplanet confirmed by Kepler to have an average orbital distance within its star's habitable zone
• List of exoplanets discovered using the Kepler spacecraft
• List of exoplanets
• List of multiplanetary systems
• List of stars that dim oddly
• Hunt for Exomoons with Kepler
• William J. Borucki, the chief investigator for Kepler
• NASA Exoplanet Archive, online exoplanet catalog

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Other space-based exoplanet search projects

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• CHEOPS {{small|(since 2019)}}
• CoRoT {{small|(2006–2012)}}
• Gaia {{small|(2013–2025)}}
• PlanetQuest {{small|(since 2002)}}
• PLATO {{small|(2026)}}
• TESS {{small|(since 2018)}}

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Other ground-based exoplanet search projects

{{div col|colwidth=18em}}

• APF {{small|(since 2013)}}
• HATNet {{small|(since 2001)}}
• HARPS {{small|(since 2003)}}
• NGTS {{small|(since 2015)}}
• PlanetQuest {{small|(since 2002)}}
• SuperWASP {{small|(since 2002)}}

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{{notelist-ua}}

{{Reflist}}

{{Commons category|Kepler (spacecraft)}}

• {{Official website|http://kepler.nasa.gov}} by NASA's Ames Research Center
• [http://www.nasa.gov/kepler Kepler website] by NASA
• [https://web.archive.org/web/20121110210233/http://keplerscience.arc.nasa.gov/ Kepler Science Center] by NASA's Ames Research Center
• [http://archive.stsci.edu/kepler/ Kepler public data archive] by the Space Telescope Science Institute
• [https://archive.nytimes.com/www.nytimes.com/interactive/science/space/keplers-tally-of-planets.html Kepler – Tally of Exoplanets] (NYT; October 30, 2018)
• [http://www.mso.anu.edu.au/saga/ Strömgren survey for Asteroseismology and Galactic Archaeology]
• {{youTube|Td_YeAdygJE|Video (1:00): Kepler Orrey V (Oct 30, 2018)}}

Exoplanet catalogs and databases

• [https://exoplanetarchive.ipac.caltech.edu/ NASA Exoplanet Archive]
• [https://exoplanet.eu/home/ Extrasolar Planets Encyclopaedia] by the Paris Observatory
• [http://phl.upr.edu/projects/habitable-exoplanets-catalog The Habitable Exoplanets Catalog] by UPR Arecibo
• [http://planetquest.jpl.nasa.gov/newworldsatlas New Worlds Atlas] by the NASA/JPL PlanetQuest

{{Space observatories}}

{{Exoplanet search projects}}

{{Johannes Kepler}}

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