Rogue planet

The two first discovery papers use the names isolated planetary-mass objects (iPMO) and free-floating planets (FFP). Most astronomical papers use one of these terms. The term rogue planet is more often used for microlensing studies, which also often uses the term FFP.{{cite journal |last1=Bennett |first1=D.P. |last2=Batista |first2=V. |display-authors=etal |date=13 December 2013 |title=A Sub-Earth-Mass Moon Orbiting a Gas Giant Primary or a High Velocity Planetary System in the Galactic Bulge |journal=The Astrophysical Journal |volume=785 |issue=2 |page=155 |arxiv=1312.3951 |bibcode=2014ApJ...785..155B |doi=10.1088/0004-637X/785/2/155 |s2cid=118327512}} A press release intended for the public might use an alternative name. The discovery of at least 70 FFPs in 2021, for example, used the terms rogue planet, starless planet,{{Cite web |date=2021-12-23 |title=Billions of Starless Planets Haunt Dark Cloud Cradles |url=https://www.nao.ac.jp/en/news/science/2021/20211223-subaru.html |access-date=2023-09-09 |website=NAOJ: National Astronomical Observatory of Japan |language=en}} wandering planet and free-floating planet{{Cite web |title=Largest Collection of Free-Floating Planets Found in the Milky Way - KPNO |url=https://kpno.noirlab.edu/news/noirlab2131/ |access-date=2023-09-08 |website=kpno.noirlab.edu}} in different press releases.

Isolated planetary-mass objects (iPMO) were first discovered in 2000 by the UK team Lucas & Roche with UKIRT in the Orion Nebula.{{Cite journal |last1=Lucas |first1=P. W. |last2=Roche |first2=P. F. |date=2000-06-01 |title=A population of very young brown dwarfs and free-floating planets in Orion |journal=Monthly Notices of the Royal Astronomical Society |volume=314 |issue=4 |pages=858–864 |doi=10.1046/j.1365-8711.2000.03515.x |doi-access=free |arxiv=astro-ph/0003061 |bibcode=2000MNRAS.314..858L |s2cid=119002349 |issn=0035-8711}} In the same year the Spanish team Zapatero Osorio et al. discovered iPMOs with Keck spectroscopy in the σ Orionis cluster. The spectroscopy of the objects in the Orion Nebula was published in 2001. Both European teams are now recognized for their quasi-simultaneous discoveries. In 1999 the Japanese team Oasa et al. discovered objects in Chamaeleon I{{Cite journal |last1=Oasa |first1=Yumiko |last2=Tamura |first2=Motohide |last3=Sugitani |first3=Koji |date=1999-11-01 |title=A Deep Near-Infrared Survey of the Chamaeleon I Dark Cloud Core |journal=The Astrophysical Journal |volume=526 |issue=1 |pages=336–343 |doi=10.1086/307964 |bibcode=1999ApJ...526..336O |s2cid=120597899 |issn=0004-637X|doi-access=free }} that were spectroscopically confirmed years later in 2004 by the US team Luhman et al.{{Cite journal |last1=Luhman |first1=K. L. |last2=Peterson |first2=Dawn E. |last3=Megeath |first3=S. T. |date=2004-12-01 |title=Spectroscopic Confirmation of the Least Massive Known Brown Dwarf in Chamaeleon |url=https://ui.adsabs.harvard.edu/abs/2004ApJ...617..565L |journal=The Astrophysical Journal |volume=617 |issue=1 |pages=565–568 |doi=10.1086/425228 |arxiv=astro-ph/0411445 |bibcode=2004ApJ...617..565L |s2cid=18157277 |issn=0004-637X}}

File:Locations of the rogue planets.jpg

There are two techniques to discover free-floating planets: direct imaging and microlensing.

Astrophysicist Takahiro Sumi of Osaka University in Japan and colleagues, who form the Microlensing Observations in Astrophysics and the Optical Gravitational Lensing Experiment collaborations, published their study of microlensing in 2011. They observed 50 million stars in the Milky Way by using the {{convert|1.8|m|adj=on}} MOA-II telescope at New Zealand's Mount John Observatory and the {{convert|1.3|m|adj=on}} University of Warsaw telescope at Chile's Las Campanas Observatory. They found 474 incidents of microlensing, ten of which were brief enough to be planets of around Jupiter's size with no associated star in the immediate vicinity. The researchers estimated from their observations that there are nearly two Jupiter-mass rogue planets for every star in the Milky Way.[http://news.sciencemag.org/sciencenow/2011/05/homeless-planets-may-be-common.html?ref=hp Homeless' Planets May Be Common in Our Galaxy] {{webarchive | url=https://web.archive.org/web/20121008190445/http://news.sciencemag.org/sciencenow/2011/05/homeless-planets-may-be-common.html?ref=hp | date=8 October 2012}} by Jon Cartwright, Science Now, 18 May 2011, Accessed 20 May 2011[http://www.physorg.com/news/2011-05-class-planets.html Planets that have no stars: New class of planets discovered], Physorg.com, 18 May 2011. Accessed May 2011.{{cite journal|first=T. |last=Sumi |arxiv=1105.3544 |title=Unbound or Distant Planetary Mass Population Detected by Gravitational Microlensing |date=2011 |display-authors=etal |doi=10.1038/nature10092 |pmid=21593867 |volume=473 |issue=7347 |journal=Nature |pages=349–352 |bibcode=2011Natur.473..349S |s2cid=4422627}} One study suggested a much larger number, up to 100,000 times more rogue planets than stars in the Milky Way, though this study encompassed hypothetical objects much smaller than Jupiter.{{cite web|title=Researchers say galaxy may swarm with 'nomad planets' |url=https://www6.slac.stanford.edu/news/2012-02-23-researchers-say-galaxy-may-swarm-nomad-planets |access-date=29 February 2012 |publisher=Stanford University|date=2012-02-23}} A 2017 study by Przemek Mróz of Warsaw University Observatory and colleagues, with six times larger statistics than the 2011 study, indicates an upper limit on Jupiter-mass free-floating or wide-orbit planets of 0.25 planets per main-sequence star in the Milky Way.{{cite journal|author=P. Mroz |arxiv=1707.07634 |title=No large population of unbound or wide-orbit Jupiter-mass planets |date=2017 |display-authors=etal |doi=10.1038/nature23276 |pmid=28738410 |volume=548 |issue=7666 |journal=Nature |pages=183–186 |bibcode=2017Natur.548..183M|s2cid=4459776}}

In September 2020, astronomers using microlensing techniques reported the detection, for the first time, of an Earth-mass rogue planet (named OGLE-2016-BLG-1928) unbound to any star and free floating in the Milky Way galaxy.{{cite journal |last1=Mróz |first1=Przemek |last2=Poleski |first2=Radosław |last3=Gould |first3=Andrew |last4=Udalski |first4=Andrzej |last5=Sumi |first5=Takahiro |last6=Szymański |first6=Michał K. |last7=Soszyński |first7=Igor |last8=Pietrukowicz |first8=Paweł |last9=Kozłowski |first9=Szymon |last10=Skowron |first10=Jan |last11=Ulaczyk |first11=Krzysztof |last12=Albrow |first12=Michael D. |last13=Chung |first13=Sun-Ju |last14=Han |first14=Cheongho |last15=Hwang |first15=Kyu-Ha |display-authors=1 |year=2020 |title=A Terrestrial-mass Rogue Planet Candidate Detected in the Shortest-timescale Microlensing Event |journal=The Astrophysical Journal Letters |volume=903 |issue=1 |at=L11 |arxiv=2009.12377 |bibcode=2020ApJ...903L..11M |doi=10.3847/2041-8213/abbfad |bibcode-access=free |doi-access=free |last16=Jung |first16=Youn Kil |last17=Kim |first17=Hyoun-Woo |last18=Ryu |first18=Yoon-Hyun |last19=Shin |first19=In-Gu |last20=Shvartzvald |first20=Yossi |last21=Yee |first21=Jennifer C. |last22=Zang |first22=Weicheng |last23=Cha |first23=Sang-Mok |last24=Kim |first24=Dong-Jin |last25=Kim |first25=Seung-Lee |last26=Lee |first26=Chung-Uk |last27=Lee |first27=Dong-Joo |last28=Lee |first28=Yongseok |last29=Park |first29=Byeong-Gon |last30=Pogge |first30=Richard W.}}{{cite news |last=Gough |first=Evan |date=1 October 2020 |title=A Rogue Earth-Mass Planet Has Been Discovered Freely Floating in the Milky Way Without a Star |work=Universe Today |url=https://www.universetoday.com/148097/a-rogue-earth-mass-planet-has-been-discovered-freely-floating-in-the-milky-way-without-a-star/ |access-date=2 October 2020}}{{cite news|last=Redd |first=Nola Taylor |title=Rogue Rocky Planet Found Adrift in the Milky Way – The diminutive world and others like it could help astronomers probe the mysteries of planet formation |url=https://www.scientificamerican.com/article/rogue-rocky-planet-found-adrift-in-the-milky-way/|date=19 October 2020 |work=Scientific American |access-date=19 October 2020}}

File:WISE J0830+2837 Spitzer.jpg. It has a temperature of 300-350 K (27-77°C; 80-170 °F).]]

Microlensing planets can only be studied by the microlensing event, which makes the characterization of the planet difficult. Astronomers therefore turn to isolated planetary-mass objects (iPMO) that were found via the direct imaging method. To determine a mass of a brown dwarf or iPMO one needs for example the luminosity and the age of an object.{{Cite journal |last1=Saumon |first1=D. |last2=Marley |first2=Mark S. |date=2008-12-01 |title=The Evolution of L and T Dwarfs in Color-Magnitude Diagrams |url=https://ui.adsabs.harvard.edu/abs/2008ApJ...689.1327S |journal=The Astrophysical Journal |volume=689 |issue=2 |pages=1327–1344 |doi=10.1086/592734 |arxiv=0808.2611 |bibcode=2008ApJ...689.1327S |s2cid=15981010 |issn=0004-637X}} Determining the age of a low-mass object has proven to be difficult. It is no surprise that the vast majority of iPMOs are found inside young nearby star-forming regions of which astronomers know their age. These objects are younger than 200 Myrs, are massive (>5 {{Jupiter mass|link=true}}) and belong to the L- and T-dwarfs. There is however a small growing sample of cold and old Y-dwarfs that have estimated masses of 8-20 {{Jupiter mass}}.{{Cite journal |last1=Leggett |first1=S. K. |last2=Tremblin |first2=P. |last3=Esplin |first3=T. L. |last4=Luhman |first4=K. L. |last5=Morley |first5=Caroline V. |date=2017-06-01 |title=The Y-type Brown Dwarfs: Estimates of Mass and Age from New Astrometry, Homogenized Photometry, and Near-infrared Spectroscopy |journal=The Astrophysical Journal |volume=842 |issue=2 |page=118 |doi=10.3847/1538-4357/aa6fb5 |arxiv=1704.03573 |bibcode=2017ApJ...842..118L |issn=0004-637X |doi-access=free }} Nearby rogue planet candidates of spectral type Y include WISE 0855−0714 at a distance of {{val|7.27|0.13|u=light-years}}.{{cite journal|title=The Spectral Energy Distribution of the Coldest Known Brown Dwarf |journal=The Astronomical Journal |first1=Kevin L. |last1=Luhman |first2=Taran L. |last2=Esplin |volume=152 |issue=2 |at=78 |date=September 2016 |doi=10.3847/0004-6256/152/3/78 |bibcode=2016AJ....152...78L |arxiv=1605.06655|s2cid=118577918 |doi-access=free }} If this sample of Y-dwarfs can be characterized with more accurate measurements or if a way to better characterize their ages can be found, the number of old and cold iPMOs will likely increase significantly.

The first iPMOs were discovered in the early 2000s via direct imaging inside young star-forming regions. These iPMOs found via direct imaging formed probably like stars (sometimes called sub-brown dwarf). There might be iPMOs that form like a planet, which are then ejected. These objects will however be kinematically different from their natal star-forming region, should not be surrounded by a circumstellar disk and have high metallicity.{{Cite journal |last=Caballero |first=José A. |date=2018-09-01 |title=A Review on Substellar Objects below the Deuterium Burning Mass Limit: Planets, Brown Dwarfs or What? |journal=Geosciences |volume=8 |issue=10 |page=362 |doi=10.3390/geosciences8100362 |arxiv=1808.07798 |bibcode=2018Geosc...8..362C |doi-access=free }} None of the iPMOs found inside young star-forming regions show a high velocity compared to their star-forming region. For old iPMOs the cold WISE J0830+2837 shows a V_tan of about 100 km/s, which is high, but still consistent with formation in our galaxy. For WISE 1534–1043{{Cite journal |last1=Kirkpatrick |first1=J. Davy |last2=Marocco |first2=Federico |last3=Caselden |first3=Dan |last4=Meisner |first4=Aaron M. |last5=Faherty |first5=Jacqueline K. |last6=Schneider |first6=Adam C. |last7=Kuchner |first7=Marc J. |last8=Casewell |first8=S. L. |last9=Gelino |first9=Christopher R. |last10=Cushing |first10=Michael C. |last11=Eisenhardt |first11=Peter R. |last12=Wright |first12=Edward L. |last13=Schurr |first13=Steven D. |date=2021-07-01 |title=The Enigmatic Brown Dwarf WISEA J153429.75-104303.3 (a.k.a. "The Accident") |journal=The Astrophysical Journal |volume=915 |issue=1 |pages=L6 |doi=10.3847/2041-8213/ac0437 |arxiv=2106.13408 |bibcode=2021ApJ...915L...6K |issn=0004-637X |doi-access=free }} one alternative scenario explains this object as an ejected exoplanet due to its high V_tan of about 200 km/s, but its color suggests it is an old metal-poor brown dwarf. Most astronomers studying massive iPMOs believe that they represent the low-mass end of the star-formation process.

Astronomers have used the Herschel Space Observatory and the Very Large Telescope to observe a very young free-floating planetary-mass object, OTS 44, and demonstrate that the processes characterizing the canonical star-like mode of formation apply to isolated objects down to a few Jupiter masses. Herschel far-infrared observations have shown that OTS 44 is surrounded by a disk of at least 10 Earth masses and thus could eventually form a mini planetary system.{{cite journal |last1=Joergens |first1=V. |last2=Bonnefoy |first2=M. |last3=Liu |first3=Y. |last4=Bayo |first4=A. |last5=Wolf |first5=S. |last6=Chauvin |first6=G. |last7=Rojo |first7=P. |date=2013 |title=OTS 44: Disk and accretion at the planetary border |journal=Astronomy & Astrophysics |volume=558 |page=L7 |arxiv=1310.1936 |bibcode=2013A&A...558L...7J |doi=10.1051/0004-6361/201322432 |s2cid=118456052 |number=7}} Spectroscopic observations of OTS 44 with the SINFONI spectrograph at the Very Large Telescope have revealed that the disk is actively accreting matter, similar to the disks of young stars.

{{multiple image

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| image1 = TWA 42 Keck.png

| caption1 = 2MASS J1119–1137AB, the first planetary-mass binary discovered, located in the TW Hydrae association

| image2 = JuMBO 29.jpg

| caption2 = JuMBO 29, a candidate 12.5+3 {{jupiter mass}} binary, separated by 135 AU, located in the Orion Nebula

}}

The first discovery of a resolved planetary-mass binary was 2MASS J1119–1137AB. There are however other binaries known, such as 2MASS J1553022+153236AB,{{Cite journal |last1=Dupuy |first1=Trent J. |last2=Liu |first2=Michael C. |date=2012-08-01 |title=The Hawaii Infrared Parallax Program. I. Ultracool Binaries and the L/T Transition |journal=The Astrophysical Journal Supplement Series |volume=201 |issue=2 |page=19 |arxiv=1201.2465 |bibcode=2012ApJS..201...19D |doi=10.1088/0067-0049/201/2/19 |issn=0067-0049 |doi-access=free}}{{Cite journal |last1=Zhang |first1=Zhoujian |last2=Liu |first2=Michael C. |last3=Best |first3=William M. J. |last4=Dupuy |first4=Trent J. |last5=Siverd |first5=Robert J. |date=2021-04-01 |title=The Hawaii Infrared Parallax Program. V. New T-dwarf Members and Candidate Members of Nearby Young Moving Groups |journal=The Astrophysical Journal |volume=911 |issue=1 |page=7 |arxiv=2102.05045 |bibcode=2021ApJ...911....7Z |doi=10.3847/1538-4357/abe3fa |issn=0004-637X |doi-access=free}} WISE 1828+2650, WISE 0146+4234, WISE J0336−0143 (could also be a brown dwarf and a planetary-mass object (BD+PMO) binary), NIRISS-NGC1333-12{{Cite journal |last1=Langeveld |first1=Adam B. |last2=Scholz |first2=Aleks |last3=Mužić |first3=Koraljka |last4=Jayawardhana |first4=Ray |last5=Capela |first5=Daniel |last6=Albert |first6=Loïc |last7=Doyon |first7=René |last8=Flagg |first8=Laura |last9=de Furio |first9=Matthew |last10=Johnstone |first10=Doug |last11=Lafrèniere |first11=David |last12=Meyer |first12=Michael |date=2024-10-01 |title=The JWST/NIRISS Deep Spectroscopic Survey for Young Brown Dwarfs and Free-floating Planets |journal=The Astronomical Journal |volume=168 |issue=4 |page=179 |arxiv=2408.12639 |bibcode=2024AJ....168..179L |doi=10.3847/1538-3881/ad6f0c |doi-access=free |issn=0004-6256}} and several objects discovered by Zhang et al.

In the Orion Nebula a population of 40 wide binaries and 2 triple systems were discovered. The discovery was surprising for two reasons: the trend of binaries of brown dwarfs predicted a decrease of distance between low mass objects with decreasing mass. It was also predicted that the binary fraction decreases with mass. These binaries were named Jupiter-mass Binary Objects (JuMBOs); they make up at least 9% of the iPMOs and have a separation smaller than 340 AU. It is unclear how these JuMBOs formed, but an extensive study argued that they formed in situ, like stars.{{Cite journal | last1=Portegies Zwart| first1=Simon|last2=Hochart|first2=Erwan|date=2024-07-02|title=The origin and evolution of wide Jupiter mass binary objects in young stellar clusters| journal=SciPost| volume=3|issue=1|page=19|doi=10.21468/SciPostAstro.3.1.001| doi-access=free| arxiv=2312.04645| bibcode=2024ScPA....3....1P}} If they formed like stars, then there must be an unknown "extra ingredient" to allow them to form. If they formed like planets and were later ejected, then it has to be explained why these binaries did not break apart during the ejection process. Future measurements with JWST might resolve if these objects formed as ejected planets or as stars.{{Cite arXiv |last1=Pearson |first1=Samuel G. |last2=McCaughrean |first2=Mark J. |date=2 Oct 2023 |title=Jupiter Mass Binary Objects in the Trapezium Cluster |page=24 |class=astro-ph.EP |eprint=2310.01231 }} Kevin Luhman reanalysed the NIRCam data and found that most JuMBOs did not appear in his sample of substellar objects. Moreover the color was consistent with reddened background sources or low signal-to-noise sources. He considers only JuMBO 29 as a good candidate for a binary planetary-mass system.{{cite journal| last = Luhman | first =K. L. | author-link=Kevin Luhman| date =14 Oct 2024 | title =Candidates for Substellar Members of the Orion Nebula Cluster from JWST/NIRCam | journal =The Astronomical Journal | volume =168 | issue =6 | page =230 | doi =10.3847/1538-3881/ad812a | doi-access =free | arxiv =2410.10406 | bibcode =2024AJ....168..230L }}

There are likely hundreds of known candidate iPMOs, over a hundred{{Cite book |last1=Béjar |first1=V. J. S. |url=https://ui.adsabs.harvard.edu/abs/2018haex.bookE..92B |title=Brown Dwarfs and Free-Floating Planets in Young Stellar Clusters |last2=Martín |first2=Eduardo L. |date=2018-01-01|bibcode=2018haex.bookE..92B }} objects with spectra and a small but growing number of candidates discovered via microlensing. Some large surveys include:

As of December 2021, the largest-ever group of rogue planets was discovered, numbering at least 70 and up to 170 depending on the assumed age. They are found in the OB association between Upper Scorpius and Ophiuchus with masses between 4 and 13 {{Jupiter mass|link=y}} and age around 3 to 10 million years, and were most likely formed by either gravitational collapse of gas clouds, or formation in a protoplanetary disk followed by ejection due to dynamical instabilities.{{Cite journal|last1=Miret-Roig|first1=Núria|last2=Bouy|first2=Hervé|last3=Raymond|first3=Sean N.|last4=Tamura|first4=Motohide|last5=Bertin|first5=Emmanuel|last6=Barrado|first6=David|last7=Olivares|first7=Javier|last8=Galli|first8=Phillip A. B.|last9=Cuillandre|first9=Jean-Charles|last10=Sarro|first10=Luis Manuel|last11=Berihuete|first11=Angel|date=2021-12-22|title=A rich population of free-floating planets in the Upper Scorpius young stellar association|url=https://www.nature.com/articles/s41550-021-01513-x|journal=Nature Astronomy|volume=6|pages=89–97|language=en|doi=10.1038/s41550-021-01513-x|issn=2397-3366|bibcode=2022NatAs...6...89M|arxiv=2112.11999|s2cid=245385321}} See also

[https://www.nature.com/articles/s41550-021-01513-x.epdf?sharing_token=q1qRU1u0E-F1gidMR-zy99RgN0jAjWel9jnR3ZoTv0MNRjP5-PHrAStec6uGZjltVbis6xlDrJ6k1jF8hqqq10sjBO3UdEZIpgGDRm7TPS_gSCK_FYKPReCzFKzmtRjs42WI3U-Sq54AafvVIZd1723041mlBJXX5KXeJj4Y7aQ%3D Nature SharedIt article link];

[https://www.eso.org/public/archives/releases/sciencepapers/eso2120/eso2120a_en.pdf ESO article link]{{cite web | title = ESO telescopes help uncover largest group of rogue planets yet | url = https://www.eso.org/public/news/eso2120/ | publisher = European Southern Observatory | date = 22 December 2021 | access-date = 22 December 2021}}{{Cite web|last1=Raymond|first1=Sean|last2=Bouy|first2=Núria Miret-Roig & Hervé|date=2021-12-22|title=We Discovered a Rogues' Gallery of Monster-Sized Gas Giants|url=http://nautil.us/blog/we-discovered-a-rogues-gallery-of-monster_sized-gas-giants|access-date=2021-12-23|website=Nautilus}}{{Cite web|last=Shen|first=Zili|date=2021-12-30|title=Wandering Planets|url=https://astrobites.org/2021/12/30/free-floating-planets/|access-date=2022-01-02|website=Astrobites|language=en-US}} Follow-up observations with spectroscopy from the Subaru Telescope and Gran Telescopio Canarias showed that the contamination of this sample is quite low (≤6%). The 16 young objects had a mass between 3 and 14 {{Jupiter mass}}, confirming that they are indeed planetary-mass objects.

In October 2023 an even larger group of 540 planetary-mass object candidates was discovered in the Trapezium Cluster and inner Orion Nebula with JWST. The objects have a mass between 13 and 0.6 {{Jupiter mass}}. A surprising number of these objects formed wide binaries, which was not predicted.

There are in general two scenarios that can lead to the formation of an isolated planetary-mass object (iPMO). It can form like a planet around a star and is then ejected, or it forms like a low-mass star or brown dwarf in isolation. This can influence its composition and motion.

{{Main|Sub-brown dwarf}}

Objects with a mass of at least one Jupiter mass were thought to be able to form via collapse and fragmentation of molecular clouds from models in 2001.{{Cite journal |last=Boss |first=Alan P. |date=2001-04-01 |title=Formation of Planetary-Mass Objects by Protostellar Collapse and Fragmentation |journal=The Astrophysical Journal |volume=551 |issue=2 |pages=L167–L170 |doi=10.1086/320033 |bibcode=2001ApJ...551L.167B |s2cid=121261733 |issn=0004-637X|doi-access=free }} Pre-JWST observations have shown that objects below 3-5 {{Jupiter mass}} are unlikely to form on their own. Observations in 2023 in the Trapezium Cluster with JWST have shown that objects as massive as 0.6 {{Jupiter mass}} might form on their own, not requiring a steep cut-off mass. A particular type of globule, called globulettes, are thought to be birthplaces for brown dwarfs and planetary-mass objects. Globulettes are found in the Rosette Nebula and IC 1805.{{Cite journal |last1=Gahm |first1=G. F. |last2=Grenman |first2=T. |last3=Fredriksson |first3=S. |last4=Kristen |first4=H. |date=2007-04-01 |title=Globulettes as Seeds of Brown Dwarfs and Free-Floating Planetary-Mass Objects |journal=The Astronomical Journal |volume=133 |issue=4 |pages=1795–1809 |doi=10.1086/512036 |bibcode=2007AJ....133.1795G |s2cid=120588285 |issn=0004-6256|doi-access=free }} Sometimes young iPMOs are still surrounded by a disk that could form exomoons. Due to the tight orbit of this type of exomoon around their host planet, they have a high chance of 10-15% to be transiting.{{Cite journal |last1=Limbach |first1=Mary Anne |last2=Vos |first2=Johanna M. |last3=Winn |first3=Joshua N. |last4=Heller |first4=René |last5=Mason |first5=Jeffrey C. |last6=Schneider |first6=Adam C. |last7=Dai |first7=Fei |date=2021-09-01 |title=On the Detection of Exomoons Transiting Isolated Planetary-mass Objects |journal=The Astrophysical Journal |volume=918 |issue=2 |pages=L25 |doi=10.3847/2041-8213/ac1e2d |arxiv=2108.08323 |bibcode=2021ApJ...918L..25L |issn=0004-637X |doi-access=free }}

Some very young star-forming regions, typically younger than 5 million years, sometimes contain isolated planetary-mass objects with infrared excess and signs of accretion. Most well known is the iPMO OTS 44 discovered to have a disk and being located in Chamaeleon I. Chamaeleon I and II have other candidate iPMOs with disks.{{Cite journal |last1=Luhman |first1=K. L. |last2=Adame |first2=Lucía |last3=D'Alessio |first3=Paola |last4=Calvet |first4=Nuria |last5=Hartmann |first5=Lee |last6=Megeath |first6=S. T. |last7=Fazio |first7=G. G. |date=2005-12-01 |title=Discovery of a Planetary-Mass Brown Dwarf with a Circumstellar Disk |journal=The Astrophysical Journal |volume=635 |issue=1 |pages=L93–L96 |doi=10.1086/498868 |bibcode=2005ApJ...635L..93L |issn=0004-637X|doi-access=free |arxiv=astro-ph/0511807 }}{{Cite journal |last1=Jayawardhana |first1=Ray |last2=Ivanov |first2=Valentin D. |date=2006-08-01 |title=Spectroscopy of Young Planetary Mass Candidates with Disks |journal=The Astrophysical Journal |volume=647 |issue=2 |pages=L167–L170 |doi=10.1086/507522 |bibcode=2006ApJ...647L.167J |issn=0004-637X|doi-access=free |arxiv=astro-ph/0607152 }} Other star-forming regions with iPMOs with disks or accretion are Lupus I, Rho Ophiuchi Cloud Complex,{{Cite journal |last1=Rilinger |first1=Anneliese M. |last2=Espaillat |first2=Catherine C. |date=2021-11-01 |title=Disk Masses and Dust Evolution of Protoplanetary Disks around Brown Dwarfs |journal=The Astrophysical Journal |volume=921 |issue=2 |page=182 |doi=10.3847/1538-4357/ac09e5 |bibcode=2021ApJ...921..182R |issn=0004-637X |doi-access=free |arxiv=2106.05247 }} Sigma Orionis cluster,{{Cite journal |last1=Zapatero Osorio |first1=M. R. |last2=Caballero |first2=J. A. |last3=Béjar |first3=V. J. S. |last4=Rebolo |first4=R. |last5=Barrado Y Navascués |first5=D. |last6=Bihain |first6=G. |last7=Eislöffel |first7=J. |last8=Martín |first8=E. L. |last9=Bailer-Jones |first9=C. A. L. |last10=Mundt |first10=R. |last11=Forveille |first11=T. |last12=Bouy |first12=H. |date=2007-09-01 |title=Discs of planetary-mass objects in σ Orionis |journal=Astronomy and Astrophysics |volume=472 |issue=1 |pages=L9–L12 |doi=10.1051/0004-6361:20078116 |bibcode=2007A&A...472L...9Z |issn=0004-6361|doi-access=free }} Orion Nebula, Taurus,{{Cite journal |last1=Best |first1=William M. J. |last2=Liu |first2=Michael C. |last3=Magnier |first3=Eugene A. |last4=Bowler |first4=Brendan P. |last5=Aller |first5=Kimberly M. |last6=Zhang |first6=Zhoujian |last7=Kotson |first7=Michael C. |last8=Burgett |first8=W. S. |last9=Chambers |first9=K. C. |last10=Draper |first10=P. W. |last11=Flewelling |first11=H. |last12=Hodapp |first12=K. W. |last13=Kaiser |first13=N. |last14=Metcalfe |first14=N. |last15=Wainscoat |first15=R. J. |date=2017-03-01 |title=A Search for L/T Transition Dwarfs with Pan-STARRS1 and WISE. III. Young L Dwarf Discoveries and Proper Motion Catalogs in Taurus and Scorpius-Centaurus |journal=The Astrophysical Journal |volume=837 |issue=1 |page=95 |doi=10.3847/1538-4357/aa5df0 |bibcode=2017ApJ...837...95B |issn=0004-637X |doi-access=free |arxiv=1702.00789 |hdl=1721.1/109753 |hdl-access=free }} NGC 1333{{Cite journal |last1=Scholz |first1=Aleks |last2=Muzic |first2=Koraljka |last3=Jayawardhana |first3=Ray |last4=Almendros-Abad |first4=Victor |last5=Wilson |first5=Isaac |date=2023-05-01 |title=Disks around Young Planetary-mass Objects: Ultradeep Spitzer Imaging of NGC 1333 |journal=The Astronomical Journal |volume=165 |issue=5 |page=196 |doi=10.3847/1538-3881/acc65d |bibcode=2023AJ....165..196S |issn=0004-6256 |doi-access=free |arxiv=2303.12451 |hdl=10023/27429 |hdl-access=free }} and IC 348.{{Cite journal |last1=Alves de Oliveira |first1=C. |last2=Moraux |first2=E. |last3=Bouvier |first3=J. |last4=Duchêne |first4=G. |last5=Bouy |first5=H. |last6=Maschberger |first6=T. |last7=Hudelot |first7=P. |date=2013-01-01 |title=Spectroscopy of brown dwarf candidates in IC 348 and the determination of its substellar IMF down to planetary masses |journal=Astronomy and Astrophysics |volume=549 |pages=A123 |doi=10.1051/0004-6361/201220229 |bibcode=2013A&A...549A.123A |issn=0004-6361|doi-access=free |arxiv=1211.4029 }} A large survey of disks around brown dwarfs and iPMOs with ALMA found that these disks are not massive enough to form earth-mass planets. There is still the possibility that the disks already have formed planets. Studies of red dwarfs have shown that some have gas-rich disks at a relative old age. These disks were dubbed Peter Pan Disks and this trend could continue into the planetary-mass regime. One Peter Pan disk is the 45 Myr old brown dwarf 2MASS J02265658-5327032 with a mass of about 13.7 {{Jupiter mass}}, which is close to the planetary-mass regime.{{Cite journal |last1=Boucher |first1=Anne |last2=Lafrenière |first2=David |last3=Gagné |first3=Jonathan |last4=Malo |first4=Lison |last5=Faherty |first5=Jacqueline K. |last6=Doyon |first6=René |last7=Chen |first7=Christine H. |date=2016-11-01 |title=BANYAN. VIII. New Low-mass Stars and Brown Dwarfs with Candidate Circumstellar Disks |journal=The Astrophysical Journal |volume=832 |issue=1 |page=50 |doi=10.3847/0004-637X/832/1/50 |bibcode=2016ApJ...832...50B |issn=0004-637X |doi-access=free |arxiv=1608.08259 }} Recent studies of the nearby planetary-mass object 2MASS J11151597+1937266 found that this nearby iPMO is surrounded by a disk. It shows signs of accretion from the disk and also infrared excess.{{Cite journal |last1=Theissen |first1=Christopher A. |last2=Burgasser |first2=Adam J. |last3=Bardalez Gagliuffi |first3=Daniella C. |last4=Hardegree-Ullman |first4=Kevin K. |last5=Gagné |first5=Jonathan |last6=Schmidt |first6=Sarah J. |last7=West |first7=Andrew A. |date=2018-01-01 |title=2MASS J11151597+1937266: A Young, Dusty, Isolated, Planetary-mass Object with a Potential Wide Stellar Companion |journal=The Astrophysical Journal |volume=853 |issue=1 |page=75 |arxiv=1712.03964 |bibcode=2018ApJ...853...75T |doi=10.3847/1538-4357/aaa0cf |issn=0004-637X |doi-access=free}} In May 2025 researchers using JWST found that the disk around Cha 1107−7626 contains hydrocarbons. Cha 1107−7626 (6-10 {{Jupiter mass}}) is one of the lowest-mass objects with a dusty disk.{{Cite arXiv |eprint=2505.13714 |last1=Flagg |first1=Laura |last2=Scholz |first2=Aleks |last3=Almendros-Abad |first3=V. |last4=Jayawardhana |first4=Ray |last5=Damian |first5=Belinda |last6=Muzic |first6=Koraljka |last7=Natta |first7=Antonella |last8=Pinilla |first8=Paola |last9=Testi |first9=Leonardo |title=Detection of Hydrocarbons in the Disk around an Actively-Accreting Planetary-Mass Object |date=2025 |class=astro-ph.EP }}

Ejected planets are predicted to be mostly low-mass (<30 {{Earth mass|link=true}} Figure 1 Ma et al.){{Cite journal |last1=Ma |first1=Sizheng |last2=Mao |first2=Shude |last3=Ida |first3=Shigeru |last4=Zhu |first4=Wei |last5=Lin |first5=Douglas N. C. |date=2016-09-01 |title=Free-floating planets from core accretion theory: microlensing predictions |journal=Monthly Notices of the Royal Astronomical Society |volume=461 |issue=1 |pages=L107–L111 |doi=10.1093/mnrasl/slw110 |doi-access=free |arxiv=1605.08556 |bibcode=2016MNRAS.461L.107M |issn=0035-8711}} and their mean mass depends on the mass of their host star. Simulations by Ma et al. did show that 17.5% of 1 {{Solar mass|link=true}} stars eject a total of 16.8 {{Earth mass}} per star with a typical (median) mass of 0.8 {{Earth mass}} for an individual free-floating planet (FFP). For lower mass red dwarfs with a mass of 0.3 {{Solar mass}} 12% of stars eject a total of 5.1 {{Earth mass}} per star with a typical mass of 0.3 {{Earth mass}} for an individual FFP.

Hong et al.{{Cite journal |last1=Hong |first1=Yu-Cian |last2=Raymond |first2=Sean N. |last3=Nicholson |first3=Philip D. |last4=Lunine |first4=Jonathan I. |date=2018-01-01 |title=Innocent Bystanders: Orbital Dynamics of Exomoons During Planet-Planet Scattering |journal=The Astrophysical Journal |volume=852 |issue=2 |page=85 |doi=10.3847/1538-4357/aaa0db |arxiv=1712.06500 |bibcode=2018ApJ...852...85H |issn=0004-637X |doi-access=free }} predicted that exomoons can be scattered by planet-planet interactions and become ejected exomoons. Higher mass (0.3-1 {{Jupiter mass}}) ejected FFP are predicted to be possible, but they are also predicted to be rare. Ejection of a planet can occur via planet-planet scatter or due a stellar flyby. Another possibility is the ejection of a fragment of a disk that then forms into a planetary-mass object.{{Cite journal |last=Miret-Roig |first=Núria |date=2023-03-01 |title=The origin of free-floating planets |url=https://ui.adsabs.harvard.edu/abs/2023Ap&SS.368...17M/abstract |journal=Astrophysics and Space Science |volume=368 |issue=3 |page=17 |arxiv=2303.05522 |bibcode=2023Ap&SS.368...17M |doi=10.1007/s10509-023-04175-5 |issn=0004-640X}} Another suggested scenario is the ejection of planets in a tilted circumbinary orbit. Interactions with the central binary and the planets with each other can lead to the ejection of the lower-mass planet in the system.{{Cite journal |last1=Chen |first1=Cheng |last2=Martin |first2=Rebecca G. |last3=Lubow |first3=Stephen H. |last4=Nixon |first4=C. J. |date=2024-01-01 |title=Tilted Circumbinary Planetary Systems as Efficient Progenitors of Free-floating Planets |journal=The Astrophysical Journal |volume=961 |issue=1 |pages=L5 |arxiv=2310.15603 |bibcode=2024ApJ...961L...5C |doi=10.3847/2041-8213/ad17c5 |doi-access=free |issn=0004-637X}}{{cite journal |last1=Portegies Zwart |first1=Simon |last2=Hochart |first2=Erwan |date=2 July 2024 |title=The origin and evolution of wide Jupiter mass binary objects in young stellar clusters |journal=SciPost Astronomy |volume=3 |issue=1 |doi=10.21468/SciPostAstro.3.1.001|doi-access=free |bibcode=2024ScPA....3....1P |arxiv=2312.04645 }} Although the effectiveness of this mechanism depends on the encounter geometry, which is not well constrained yet both observationally and theoretically

Encounters between young circumstellar disks, which are marginally gravitationally stable, can produce elongated tidal bridges that collapse locally to form iPMOs.{{cite news |title=PMO |url=https://www.news.uzh.ch/en/articles/media/2025/PMO.html |work=www.news.uzh.ch |date=27 February 2025 |language=en}} These iPMOs host expansive disks similar to observations, which the ejected planet hyperthesis can hardly explain. They also have a high multiplicity fraction in their formation, as suggested by iPMOs in the Trapezium cluster. Although the effectiveness of this mechanism depends on the encounter geometry, which is not well constrained yet both observationally and theoretically.{{cite journal |last1=Fu |first1=Zhihao |last2=Deng |first2=Hongping |last3=Lin |first3=Douglas N. C. |last4=Mayer |first4=Lucio |title=Formation of free-floating planetary mass objects via circumstellar disk encounters |journal=Science Advances |date=28 February 2025 |volume=11 |issue=9 |pages=eadu6058 |doi=10.1126/sciadv.adu6058|pmid=40009673 |pmc=11864182 |arxiv=2410.21180 |bibcode=2025SciA...11.6058F }}

If a stellar or brown dwarf embryo experiences a halted accretion, it could remain low-mass enough to become a planetary-mass object. Such a halted accretion could occur if the embryo is ejected or if its circumstellar disk experiences photoevaporation near O-stars. Objects that formed via the ejected embryo scenario would have smaller or no disk and the fraction of binaries decreases for such objects. It could also be that free-floating planetary-mass objects form from a combination of scenarios.

Most isolated planetary-mass objects will float in interstellar space forever.

Some iPMOs will have a close encounter with a planetary system. This rare encounter can have three outcomes: The iPMO will remain unbound, it could be weakly bound to the star, or it could "kick out" the exoplanet, replacing it. Simulations have shown that the vast majority of these encounters result in a capture event with the iPMO being weakly bound with a low gravitational binding energy and an elongated highly eccentric orbit. These orbits are not stable and 90% of these objects gain energy due to planet-planet encounters and are ejected back into interstellar space. Only 1% of all stars will experience this temporary capture.{{Cite journal |last1=Goulinski |first1=Nadav |last2=Ribak |first2=Erez N. |date=2018-01-01 |title=Capture of free-floating planets by planetary systems |journal=Monthly Notices of the Royal Astronomical Society |volume=473 |issue=2 |pages=1589–1595 |doi=10.1093/mnras/stx2506 |doi-access=free |bibcode=2018MNRAS.473.1589G |issn=0035-8711|arxiv=1705.10332 }}

File:Alone in Space - Astronomers Find New Kind of Planet.jpg-size rogue planet]]

Interstellar planets generate little heat and are not heated by a star.{{cite web |url=https://aeon.co/essays/could-we-make-our-home-on-a-rogue-planet-without-a-sun |title=Life in the dark |publisher=Aeon |first=Sean |last=Raymond |date=9 April 2005 |access-date=9 April 2016}} However, in 1998, David J. Stevenson theorized that some planet-sized objects adrift in interstellar space might sustain a thick atmosphere that would not freeze out. He proposed that these atmospheres would be preserved by the pressure-induced far-infrared radiation opacity of a thick hydrogen-containing atmosphere.{{cite journal |journal=Nature |date=1999 |title=Life-sustaining planets in interstellar space? |first1=David J. |last1=Stevenson |doi=10.1038/21811 |volume=400 |page=32 |last2=Stevens |first2=C. F. |issue=6739 |bibcode=1999Natur.400...32S |pmid=10403246|s2cid=4307897|doi-access=free }}

During planetary-system formation, several small protoplanetary bodies may be ejected from the system.{{cite journal|last=Lissauer |first= J. J. |title=Timescales for Planetary Accretion and the Structure of the Protoplanetary disk |journal=Icarus |volume=69 |issue=2 |pages=249–265 |date=1987 |doi=10.1016/0019-1035(87)90104-7 |bibcode=1987Icar...69..249L |hdl=2060/19870013947 |hdl-access=free}} An ejected body would receive less of the stellar-generated ultraviolet light that can strip away the lighter elements of its atmosphere. Even an Earth-sized body would have enough gravity to prevent the escape of the hydrogen and helium in its atmosphere. In an Earth-sized object the geothermal energy from residual core radioisotope decay could maintain a surface temperature above the melting point of water, allowing liquid-water oceans to exist. These planets are likely to remain geologically active for long periods. If they have geodynamo-created protective magnetospheres and sea floor volcanism, hydrothermal vents could provide energy for life. These bodies would be difficult to detect because of their weak thermal microwave radiation emissions, although reflected solar radiation and far-infrared thermal emissions may be detectable from an object that is less than 1,000 astronomical units from Earth.{{cite journal|title=The Steppenwolf: A proposal for a habitable planet in interstellar space |arxiv=1102.1108 |first1=Dorian S. |last1=Abbot |first2=Eric R. |last2=Switzer |date=2 June 2011 |doi=10.1088/2041-8205/735/2/L27 |volume=735 |issue=2 |journal=The Astrophysical Journal |page=L27 |bibcode=2011ApJ...735L..27A|s2cid=73631942 }} Around five percent of Earth-sized ejected planets with Moon-sized natural satellites would retain their satellites after ejection. A large satellite would be a source of significant geological tidal heating.{{cite journal|title=The Survival Rate of Ejected Terrestrial Planets with Moons |first=John H. |last=Debes |author2=Steinn Sigurðsson |date=20 October 2007 |journal=The Astrophysical Journal Letters |volume=668 |issue=2 |pages=L167–L170 |doi=10.1086/523103 |bibcode=2007ApJ...668L.167D |arxiv=0709.0945 |s2cid=15782213}}

The table below lists rogue planets, confirmed or suspected, that have been discovered. It is yet unknown whether these planets were ejected from orbiting a star or else formed on their own as sub-brown dwarfs. Whether exceptionally low-mass rogue planets (such as OGLE-2012-BLG-1323 and KMT-2019-BLG-2073) are even capable of being formed on their own is currently unknown.

These objects were discovered with the direct imaging method. Many were discovered in young star-clusters or stellar associations and a few old are known (such as WISE 0855−0714). List is sorted after discovery year.

These objects were discovered via microlensing. Rogue planets discovered via microlensing can only be studied by the lensing event. Some of them could also be exoplanets in a wide orbit around an unseen star.{{citation |last1=Mróz |first1=Przemek |title=A terrestrial-mass rogue planet candidate detected in the shortest-timescale microlensing event |journal=The Astrophysical Journal |volume=903 |issue=1 |pages=L11 |year=2020 |arxiv=2009.12377 |bibcode=2020ApJ...903L..11M |doi=10.3847/2041-8213/abbfad |s2cid=221971000 |display-authors=29 |last2=Poleski |first2=Radosław |last3=Gould |first3=Andrew |last4=Udalski |first4=Andrzej |last5=Sumi |first5=Takahiro |last6=Szymański |first6=Michał K. |last7=Soszyński |first7=Igor |last8=Pietrukowicz |first8=Paweł |last9=Kozłowski |first9=Szymon |last10=Skowron |first10=Jan |last11=Ulaczyk |first11=Krzysztof |last12=Albrow |first12=Michael D. |last13=Chung |first13=Sun-Ju |last14=Han |first14=Cheongho |last15=Hwang |first15=Kyu-Ha |last16=Jung |first16=Youn Kil |last17=Kim |first17=Hyoun-Woo |last18=Ryu |first18=Yoon-Hyun |last19=Shin |first19=In-Gu |last20=Shvartzvald |first20=Yossi |last21=Yee |first21=Jennifer C. |last22=Zang |first22=Weicheng |last23=Cha |first23=Sang-Mok |last24=Kim |first24=Dong-Jin |last25=Kim |first25=Seung-Lee |last26=Lee |first26=Chung-Uk |last27=Lee |first27=Dong-Joo |last28=Lee |first28=Yongseok |last29=Park |first29=Byeong-Gon |last30=Pogge |first30=Richard W. |doi-access=free }}

• {{annotated link|Intergalactic star}}
• Interstellar object – an astronomical object in interstellar space that is not gravitationally bound to a star
• ʻOumuamua – an interstellar object that passed through the Solar System in 2017
• Rogue black hole – a gravitationally unbound black hole
• Rogue extragalactic planets – rogue planets outside the Milky Way galaxy
• Tidally detached exomoon – rogue planets that were originally moons

• A Pail of Air (1951) — a science fiction short story Fritz Leiber where Earth is pulled out of the Solar System by a black hole. Although the Earth is explicitly stated to orbit the black hole, the net effect is the same as ejecting it out of the Solar System as a rogue planet.{{Cite web |title=Rogue Planets |url=https://warwick.ac.uk/fac/sci/physics/research/astro/people/stanway/sciencefiction/cosmicstories/rogue_planets |access-date=2025-04-26 |website=warwick.ac.uk}}{{Cite magazine |last=Nicoll |first=James Davis |author-link=James Nicoll |date=2020-04-30 |title=Far From Any Star: Five Stories About Rogue Worlds |url=https://reactormag.com/far-from-any-star-five-stories-about-rogue-worlds/ |access-date=2025-04-26 |magazine=Reactor |language=en-US}}
• The Secret of the Ninth Planet (1959) — novel by Donald A. Wollheim in which Pluto is revealed to be a captured rogue planet with a surviving remnant civilization{{Cite encyclopedia |year=2021 |title=Outer Planets |encyclopedia=The Encyclopedia of Science Fiction |url=https://sf-encyclopedia.com/entry/outer_planets |access-date=2023-06-13 |author1-link=David Langford |editor1-last=Clute |editor1-first=John |edition=4th |quote=For several decades Pluto came in for a certain amount of special attention as the apparent Ultima Thule of the solar system [...] Pluto, during the period when its orbit seemed to mark the outermost limit of the solar system, was popular for just that reason. |author2-last=Stableford |author2-first=Brian |author1-last=Langford |author1-first=David |author2-link=Brian Stableford |editor1-link=John Clute |editor2-last=Langford |editor2-first=David |editor2-link=David Langford |editor3-last=Sleight |editor3-first=Graham |editor3-link=Graham Sleight}}
• Space: 1999 (1975-77) — British science-fiction television programme where the Moon is ejected from the Solar System by a thermonuclear explosion
• Remina (2004–2005) – horror manga by Junji Ito featuring a sentient rogue planet capable of eating planets and stars
• Melancholia (2011) – science fiction film by Lars von Trier about a rogue planet on a collision course with Earth
• Dark Eden (2012) – a social science fiction novel by Chris Beckett
• The Wandering Earth (2019) – a science fiction film directed by Frant Gwo about Earth being artificially moved from the Solar System to the Alpha Centauri system
• Gemini Home Entertainment (2019–present) – horror anthology web series by Remy Abode, the main antagonist of which is a sentient rogue planet named "the Iris" that is masterminding an invasion of the Solar System, particularly Earth and Neptune{{Cite web |last=Womack |first=Lacey |date=2020-05-03 |title=15 Of The Best Video-Based ARGs On YouTube |url=https://screenrant.com/youtube-video-based-args-best/ |access-date=2025-04-26 |website=ScreenRant |language=en}}
• Carol & the End of the World (2023) – an animated adult comedy miniseries by Dan Guterman
• Rogue Planet (2002) - an episode of Star Trek: Enterprise

{{Reflist|30em}}

• [https://web.archive.org/web/20140529085818/http://mh-gps-p1.caltech.edu/uploads/File/People/djs/interstellar_planets.pdf "Possibility of Life Sustaining Planets in Interstellar Space"] Article by Stevenson similar to the Nature article but with more information.

{{Wiktionary|Interstellar planet}}

{{Commons category|Free-floating planets}}

• [https://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf Definition of a "Planet"] (Resolution B5 – IAU)
• [http://www.space.com/scienceastronomy/060605_planemos.html Strange New Worlds Could Make Miniature Solar Systems] Robert Roy Britt (SPACE.com) 5 June 2006 11:35 am ET
• [https://web.archive.org/web/20060820075858/http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601_release.html The IAU draft definition of "planet" and "plutons"] press release (International Astronomical Union) 2006

{{exoplanet}}

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