HD 209458 b

Spectroscopic studies first revealed the presence of a planet around HD 209458 on November 5, 1999. Astronomers had made careful photometric measurements of several stars known to be orbited by planets, in the hope that they might observe a dip in brightness caused by the transit of the planet across the star's face. This would require the planet's orbit to be inclined such that it would pass between the Earth and the star, and previously no transits had been detected.

Soon after the discovery, separate teams, one led by David Charbonneau including Timothy Brown and others, and the other by Gregory W. Henry, were able to detect a transit of the planet across the surface of the star making it the first known transiting extrasolar planet. On September 9 and 16, 1999, Charbonneau's team measured a 1.7% drop in HD 209458's brightness, which was attributed to the passage of the planet across the star. On November 8, Henry's team observed a partial transit, seeing only the ingress. Initially unsure of their results, the Henry group decided to rush their results to publication after overhearing rumors that Charbonneau had successfully seen an entire transit in September. Papers from both teams were published simultaneously in the same issue of the Astrophysical Journal. Each transit lasts about three hours, during which the planet covers about 1.5% of the star's face.

The star had been observed many times by the Hipparcos satellite, which allowed astronomers to calculate the orbital period of HD 209458 b very accurately at 3.524736 days.{{cite journal | url=http://www.iop.org/EJ/article/1538-4357/532/1/L51/995926.html | author=Castellano | title=Detection of Planetary Transits of the Star HD 209458 in the Hipparcos Data Set | journal=The Astrophysical Journal Letters | volume=532 | issue=1 | pages=L51–L53 | publisher=University of Chicago Press |date=March 2000 | doi=10.1086/312565 | pmid=10702130 | last2=Jenkins | first2=J. | last3=Trilling | first3=D. E. | last4=Doyle | first4=L. | last5=Koch | first5=D. | bibcode=2000ApJ...532L..51C| doi-access=free }}

Spectroscopic analysis had shown that the planet had a mass about 0.69 times that of Jupiter. The occurrence of transits allowed astronomers to calculate the planet's radius, which had not been possible for any previously known exoplanet, and it turned out to have a radius some 35% larger than Jupiter's. It had been previously hypothesized that hot Jupiters particularly close to their parent star should exhibit this kind of inflation due to intense heating of their outer atmosphere. Tidal heating due to its orbit's eccentricity, which may have been more eccentric at formation, may also have played a role over the past billion years.{{cite journal|title=Tidal Heating of Extra-Solar Planets| first= Brian| last= Jackson|author2=Richard Greenberg |author3=Rory Barnes | journal=Astrophysical Journal | date=2008|doi=10.1086/587641|volume=681|issue=2|pages=1631–1638|arxiv=0803.0026| bibcode=2008ApJ...681.1631J| s2cid= 42315630}}

On March 22, 2005, NASA released news that infrared light from the planet had been measured by the Spitzer Space Telescope, the first ever direct detection of light from an extrasolar planet. This was done by subtracting the parent star's constant light and noting the difference as the planet transited in front of the star and was eclipsed behind it, providing a measure of the light from the planet itself. New measurements from this observation determined the planet's temperature as at least {{Convert|750|C|K F}}. The nearly circular orbit of HD 209458 b was also confirmed.

File:Planetary transit.svg

On February 21, 2007, NASA and Nature released news that HD 209458 b was one of the first two extrasolar planets to have their spectra observed, the other one being HD 189733 b.{{Cite web|url=http://www.spitzer.caltech.edu/Media/releases/ssc2007-04/release.shtml|archive-url=https://web.archive.org/web/20070715071155/http://www.spitzer.caltech.edu/Media/releases/ssc2007-04/release.shtml|title=NASA's Spitzer First To Crack Open Light of Faraway Worlds|archive-date=July 15, 2007}} This was long seen as the first mechanism by which extrasolar but non-sentient life forms could be searched for, by way of influence on a planet's atmosphere. A group of investigators led by Jeremy Richardson of NASA's Goddard Space Flight Center spectrally measured HD 209458 b's atmosphere in the range of 7.5 to 13.2 micrometres. The results defied theoretical expectations in several ways. The spectrum had been predicted to have a peak at 10 micrometres, which would have indicated water vapor in the atmosphere, but such a peak was absent, indicating no detectable water vapor. Another unpredicted peak was observed at 9.65 micrometres, which the investigators attributed to clouds of silicate dust, a phenomenon not previously observed. Another unpredicted peak occurred at 7.78 micrometres, for which the investigators did not have an explanation. A separate team led by Mark Swain of the Jet Propulsion Laboratory reanalyzed the Richardson et al. data, and had not yet published their results when the Richardson et al. article came out, but made similar findings.

On 23 June 2010, astronomers announced they have measured a superstorm (with windspeeds of up to {{Convert|7,000|km/h|m/s mph|abbr=unit|lk=on|sigfig=1}}) for the first time in the atmosphere of HD 209458 b.{{Cite news |last=Rincon |first=Paul |url=http://news.bbc.co.uk/2/hi/science_and_environment/10393633.stm |title='Superstorm' rages on exoplanet |work=BBC News London |date=23 June 2010 |access-date=2010-06-24 }} The very high-precision observations done by ESO's Very Large Telescope and its powerful CRIRES spectrograph of carbon monoxide gas show that it is streaming at enormous speed from the extremely hot day side to the cooler night side of the planet. The observations also allow another exciting "first"—measuring the orbital speed of the exoplanet itself, providing a direct determination of its mass.

As of 2021, the spectra of planetary atmosphere taken by different instruments remains highly inconsistent, indicating either metal-poor atmosphere, temperatures below blackbody equilibrium{{citation|arxiv=2110.13548|year=2022|title=The strange case of Na I in the atmosphere of HD 209458 B|last1=Morello|first1=Giuseppe|last2=Casasayas-Barris|first2=Núria|last3=Orell-Miquel|first3=Jaume|last4=Pallé|first4=Enric|last5=Cracchiolo|first5=Gianluca|last6=Micela|first6=Giuseppina|journal=Astronomy & Astrophysics |volume=657 |pages=A97 |doi=10.1051/0004-6361/202141642 |s2cid=239885976 }} or disequilibrium atmosphere chemistry.{{citation|arxiv=2110.13443|year=2021|title=Implementation of disequilibrium chemistry to spectral retrieval code ARCiS and application to 16 exoplanet transmission spectra|last1=Kawashima|first1=Yui|last2=Min|first2=Michiel|journal=Astronomy & Astrophysics |volume=656 |pages=A90 |doi=10.1051/0004-6361/202141548 |s2cid=239885551 }}

In August 2008, the measurement of HD 209458 b's Rossiter–McLaughlin effect and hence spin–orbit angle is −4.4 ± 1.4°.{{cite journal|arxiv=0807.4929 | doi= 10.1017/S174392130802629X| title= Measuring accurate transit parameters| journal= Proceedings of the International Astronomical Union| volume= 4| pages= 99–109| year= 2009| last1= Winn| first1= Joshua N.| bibcode= 2009IAUS..253...99W| s2cid= 34144676}}{{cite journal | title=Measurement of Spin-Orbit Alignment in an Extrasolar Planetary System | last1=Winn | first1=Joshua N. | last2=Noyes | first2=Robert W. | last3=Holman | first3=Matthew J. | last4=Charbonneau | first4=David | last5=Ohta | first5=Yasuhiro | last6=Taruya | first6=Atsushi | last7=Suto | first7=Yasushi | last8=Narita | first8=Norio | last9=Turner | first9=Edwin L. | last10=Johnson | first10=John A. | last11=Marcy | first11=Geoffrey W. | last12=Butler | first12=R. Paul | last13=Vogt | first13=Steven S. | display-authors=1 | journal=The Astrophysical Journal | volume=631 | issue=2 | pages=1215–1226 | date=2005 | arxiv=astro-ph/0504555 | bibcode=2005ApJ...631.1215W | doi=10.1086/432571 | s2cid=969520 }}

The study in 2012, updated the spin-orbit angle to −5{{±|7}}°.{{citation|arxiv=1206.6105|title=Obliquities of Hot Jupiter Host Stars: Evidence for Tidal Interactions and Primordial Misalignments|year=2012|doi=10.1088/0004-637X/757/1/18|last1=Albrecht|first1=Simon|last2=Winn|first2=Joshua N.|last3=Johnson|first3=John A.|last4=Howard|first4=Andrew W.|last5=Marcy|first5=Geoffrey W.|last6=Butler|first6=R. Paul|last7=Arriagada|first7=Pamela|last8=Crane|first8=Jeffrey D.|last9=Shectman|first9=Stephen A.|last10=Thompson|first10=Ian B.|last11=Hirano|first11=Teruyuki|last12=Bakos|first12=Gaspar|last13=Hartman|first13=Joel D.|journal=The Astrophysical Journal|volume=757|issue=1|page=18|bibcode=2012ApJ...757...18A|s2cid=17174530}}

File:HD 209458 b.png

File:Oxygen_and_carbon_discovered_in_extrasolar_planet_atmosphere_blow-off.jpg

The atmosphere is at a pressure of one bar at an altitude of 1.29 Jupiter radii above the planet's center.

Where the pressure is 33±5 millibars, the atmosphere is clear (probably hydrogen) and its Rayleigh effect is detectable. At that pressure, the temperature is {{Convert|2,200|±|260|K|C F|abbr=unit|lk=off|sigfig=2}}.

Observations by the orbiting Microvariability and Oscillations of STars telescope initially limited the planet's albedo (or reflectivity) below 0.3, making it a surprisingly dark object. (The geometric albedo has since been measured to be 0.038 ± 0.045.{{Cite journal |arxiv=0807.1928 |doi=10.1017/S1743921308026318|title=Towards the Albedo of an Exoplanet: MOST Satellite Observations of Bright Transiting Exoplanetary Systems|journal=Proceedings of the International Astronomical Union|volume=4|pages=121–127|year=2009|last1=Rowe|first1=Jason F.|last2=Matthews|first2=Jaymie M.|last3=Seager|first3=Sara|last4=Sasselov|first4=Dimitar|last5=Kuschnig|first5=Rainer|last6=Guenther|first6=David B.|last7=Moffat|first7=Anthony F. J.|last8=Rucinski|first8=Slavek M.|last9=Walker|first9=Gordon A. H.|last10=Weiss|first10=Werner W.|bibcode=2009IAUS..253..121R|s2cid=17135830}}) In comparison, Jupiter has a much higher albedo of 0.52. This would suggest that HD 209458 b's upper cloud deck is either made of less reflective material than is Jupiter's, or else has no clouds and Rayleigh-scatters incoming radiation like Earth's dark ocean. Models since then have shown that between the top of its atmosphere and the hot, high pressure gas surrounding the mantle, there exists a stratosphere of cooler gas. This implies an outer shell of dark, opaque, hot clouds; usually thought to consist of vanadium and titanium oxides, but other compounds like tholins cannot be ruled out yet. A 2016 study indicates the high-altitude cloud cover is patchy with about 57 percent coverage.{{Cite journal |title=And now for the exoweather|journal=New Scientist |date=November 2018 |page=40|last1=MacDonald}} The Rayleigh-scattering heated hydrogen rests at the top of the stratosphere; the absorptive portion of the cloud deck floats above it at 25 millibars.{{Cite journal |arxiv=0803.1054 |doi=10.1086/590076|title=Determining Atmospheric Conditions at the Terminator of the Hot Jupiter HD 209458b|journal=The Astrophysical Journal|volume=686|issue=1|pages=667–673|year=2008|last1=Sing|first1=David K.|last2=Vidal-Madjar|first2=A.|last3=Lecavelier Des Etangs|first3=A.|last4=Désert|first4=J.-M.|last5=Ballester|first5=G.|last6=Ehrenreich|first6=D.|bibcode=2008ApJ...686..667S|s2cid=13958287}}

On November 27, 2001,{{cite press release |url=https://hubblesite.org/contents/news-releases/2001/news-2001-38.html |title=Hubble Makes First Direct Measurements of Atmosphere on World Around another Star |date=November 27, 2001 |publisher=Space Telescope Science Institute}} astronomers announced that they had detected sodium in the atmosphere of the planet, using observations with the Hubble Space Telescope.{{cite journal |bibcode=2002ApJ...568..377C |doi=10.1086/338770|title=Detection of an Extrasolar Planet Atmosphere |year=2002 |last1=Charbonneau |first1=David |last2=Brown |first2=Timothy M. |last3=Noyes |first3=Robert W. |last4=Gilliland |first4=Ronald L. |journal=The Astrophysical Journal |volume=568 |issue=1 |pages=377–384 |arxiv=astro-ph/0111544 |s2cid=14487268 }} This was the first planetary atmosphere outside the Solar System to be measured.{{cite journal | url=https://www.aanda.org/articles/aa/abs/2008/31/aa09762-08/aa09762-08.html |author1=I. A. G. Snellen |author2=S. Albrecht |author3=E. J. W. de Mooij |author4=R. S. Le Poole | title=Ground-based detection of sodium in the transmission spectrum of exoplanet HD 209458b| journal=Astronomy & Astrophysics | volume=487| issue=1 | date=2008 | pages=357–362 | doi=10.1051/0004-6361:200809762 | bibcode=2008A&A...487..357S|arxiv = 0805.0789 | s2cid=15668332 }} The core of the sodium line runs from pressures of 50 millibar to a microbar.{{cite journal |arxiv=0803.1054| doi=10.1086/590076| title=Determining Atmospheric Conditions at the Terminator of the Hot Jupiter HD 209458b| journal=The Astrophysical Journal| volume=686| pages=667–673| year=2008| last1=Sing| first1=David K.| last2=Vidal-Madjar| first2=A.| last3=Lecavelier Des Etangs| first3=A.| last4=Désert| first4=J.-M.| last5=Ballester| first5=G.| last6=Ehrenreich| first6=D.| issue=1| bibcode=2008ApJ...686..667S| s2cid=13958287}} This turns out to be about a third the amount of sodium at HD 189733 b.{{cite journal | journal=The Astrophysical Journal Letters |issue=673 |page=L87–L90 |date=20 January 2008| doi=10.1086/527475 | title=Sodium Absorption from the Exoplanetary Atmosphere of HD 189733b Detected in the Optical Transmission Spectrum |author1=Seth Redfield |author2=Michael Endl |author3=William D. Cochran |author4=Lars Koesterke | volume=673 | bibcode=2008ApJ...673L..87R|arxiv = 0712.0761 |s2cid=2028887 }}

The additional data did not confirm the presence of sodium in the atmosphere of HD 209458 b{{cite journal |arxiv=2002.10595 |last1=Casasayas-Barris |first1=N. |last2=Pallé |first2=Enric |last3=Yan |first3=Fei |last4=Chen |first4=Guo |last5=Luque |first5=R. |last6=Stangret |first6=M. |last7=Nagel |first7=Evangelos |last8=Zechmeister |first8=Mathias |last9=Oshagh |first9=Mahmoudreza |last10=Sanz-Forcada |first10=Jorge |last11=Nortmann |first11=Lisa |last12=Alonso-Floriano |first12=F. Javier |last13=Amado |first13=Pedro J. |last14=Caballero |first14=José A. |last15=Czesla |first15=Stefan |last16=Khalafinejad |first16=S. |last17=Lopez-Puertas |first17=Manuel |last18=Lopez-Santiago |first18=Javier |last19=Molaverdikhani |first19=Karan |last20=Montes |first20=David |last21=Quirrenbach |first21=Andreas |last22=Reiners |first22=Ansgar |last23=Ribas |first23=Ignasi |last24=Sánchez-López |first24=Alejandro |last25=Zapatero-Osorio|first25=María Rosa |title=Is there Na I in the atmosphere of HD 209458b? |journal=Astronomy & Astrophysics |year=2020 |volume=635 |pages=A206 |doi=10.1051/0004-6361/201937221 |s2cid=211296378 }} as in 2020.

In 2003–4, astronomers used the Hubble Space Telescope Imaging Spectrograph to discover an enormous ellipsoidal envelope of hydrogen, carbon and oxygen around the planet that reaches {{Convert|10,000|K|C F|abbr=unit|lk=off|sigfig=1}}. The hydrogen exosphere extends to a distance R_H=3.1 R_J, much larger than the planetary radius of 1.32 R_J.{{Cite journal|pages=933–937|doi=10.1051/0004-6361:200809460 |arxiv=0803.1831|title=New observations of the extended hydrogen exosphere of the extrasolar planet HD 209458b |journal=Astronomy and Astrophysics |volume=483 |issue=3 |year=2008 |last1=Ehrenreich |first1=D. |last2=Lecavelier Des Etangs |first2=A. |last3=Hébrard |first3=G. |last4=Désert |first4=J.-M. |last5=Vidal-Madjar |first5=A. |last6=McConnell |first6=J. C. |last7=Parkinson |first7=C. D. |last8=Ballester |first8=G. E. |last9=Ferlet |first9=R. |bibcode=2008A&A...483..933E |s2cid=16787305 }} At this temperature and distance, the Maxwell–Boltzmann distribution of particle velocities gives rise to a significant "tail" of atoms moving at speeds greater than the escape velocity. The planet is estimated to be losing about {{Convert|100|–|500|e6kg|e9lb|abbr=unit|lk=on|sigfig=1}} of hydrogen per second. Analysis of the starlight passing through the envelope shows that the heavier carbon and oxygen atoms are being blown from the planet by the extreme "hydrodynamic drag" created by its evaporating hydrogen atmosphere. The hydrogen tail streaming from the planet is approximately {{Convert|200,000|km|mi|abbr=unit|lk=off|sigfig=1}} long, which is roughly equivalent to its diameter.

It is thought that this type of atmosphere loss may be common to all planets orbiting Sun-like stars closer than around {{Convert|0.1|AU|e6km e6mi|abbr=unit|lk=off|sigfig=1}}. HD 209458 b will not evaporate entirely, although it may have lost up to about 7% of its mass over its estimated lifetime of 5 billion years. It may be possible that the planet's magnetic field may prevent this loss, because the exosphere would become ionized by the star, and the magnetic field would contain the ions from loss.{{Cite news|url = http://www.skyandtelescope.com/astronomy-news/can-magnetism-save-a-vaporizing-planet/|title = Can Magnetism Save a Vaporizing Planet?|date = September 1, 2009|access-date = Oct 30, 2014|last = Semeniuk|first = Ivan| newspaper=Sky & Telescope }}

On April 10, 2007, Travis Barman of the Lowell Observatory announced evidence that the atmosphere of HD 209458 b contained water vapor. Using a combination of previously published Hubble Space Telescope measurements and new theoretical models, Barman found strong evidence for water absorption in the planet's atmosphere.{{Cite web|url=https://www.newscientist.com/article/dn11576-first-sign-of-water-found-on-an-alien-world/|title=First sign of water found on an alien world|website=New Scientist}} His method modeled light passing directly through the atmosphere from the planet's star as the planet passed in front of it. However, this hypothesis is still being investigated for confirmation.

Barman drew on data and measurements taken by Heather Knutson, a student at Harvard University, from the Hubble Space Telescope, and applied new theoretical models to demonstrate the likelihood of water absorption in the atmosphere of the planet. The planet orbits its parent star every three and a half days, and each time it passes in front of its parent star, the atmospheric contents can be analyzed by examining how the atmosphere absorbs light passing from the star directly through the atmosphere in the direction of Earth.

According to a summary of the research, atmospheric water absorption in such an exoplanet renders it larger in appearance across one part of the infrared spectrum, compared to wavelengths in the visible spectrum. Barman took Knutson's Hubble data on HD 209458 b, applied to his theoretical model, and allegedly identified water absorption in the planet's atmosphere.

On April 24, the astronomer David Charbonneau, who led the team that made the Hubble observations, cautioned that the telescope itself may have introduced variations that caused the theoretical model to suggest the presence of water. He hoped that further observations would clear the matter up in the following months.{{cite web | url=http://www.sciam.com/article.cfm?articleID=25A261F0-E7F2-99DF-313249A4883E6A86&chanID=sa007|title=All Wet? Astronomers Claim Discovery of Earth-like Planet | author=J.R. Minkle|publisher=Scientific American | date=April 24, 2007}} As of April 2007, further investigation is being conducted.

On October 20, 2009, researchers at JPL announced the discovery of water vapor, carbon dioxide, and methane in the atmosphere.{{cite web | url=http://www.nasa.gov/mission_pages/spitzer/news/spitzer-20091020.html | title=Astronomers do it Again: Find Organic Molecules Around Gas Planet | date=October 20, 2009 | access-date=October 22, 2009 | archive-date=October 23, 2009 | archive-url=https://web.archive.org/web/20091023054554/http://www.nasa.gov/mission_pages/spitzer/news/spitzer-20091020.html | url-status=dead }}{{cite web | url=http://www.universetoday.com/2009/10/20/organic-molecules-detected-in-exoplanet-atmosphere/ |title=Organic Molecules Detected in Exoplanet Atmosphere | date=October 20, 2009}}

The refined spectra obtained in 2021 has detected instead water vapor, carbon monoxide, hydrogen cyanide, methane, ammonia{{citation|arxiv=2110.02028|year=2022|title=Retrieving the transmission spectrum of HD 209458b using CHOCOLATE: A new chromatic Doppler tomography technique|doi=10.1051/0004-6361/202141826 |last1=Esparza-Borges |first1=E. |last2=Oshagh |first2=M. |last3=Casasayas-Barris |first3=N. |last4=Pallé |first4=E. |last5=Chen |first5=G. |last6=Morello |first6=G. |last7=Santos |first7=N. C. |last8=Seidel |first8=J. V. |last9=Sozzetti |first9=A. |last10=Allart |first10=R. |last11=Figueira |first11=P. |last12=Bourrier |first12=V. |last13=Lillo-Box |first13=J. |last14=Borsa |first14=F. |last15=Zapatero Osorio |first15=M. R. |last16=Tabernero |first16=H. |last17=Demangeon |first17=O. D. S. |last18=Adibekyan |first18=V. |last19=González Hernández |first19=J. I. |last20=Mehner |first20=A. |last21=Allende Prieto |first21=C. |last22=Di Marcantonio |first22=P. |last23=Alibert |first23=Y. |last24=Cristiani |first24=S. |last25=Lo Curto |first25=G. |last26=Martins |first26=C. J. A. P. |last27=Micela |first27=G. |last28=Pepe |first28=F. |last29=Rebolo |first29=R. |last30=Sousa |first30=S. G. |journal=Astronomy & Astrophysics |volume=657 |pages=A23 |bibcode=2022A&A...657A..23E |s2cid=238354090 |display-authors=1 }} and acetylene, all consistent with the extremely high carbon to oxygen molar ratio of 1.0 (while Sun has C/O molar ratio of 0.55). If true, the HD 209458 b may be a prime example of the carbon planet.{{citation|arxiv=2104.03352|year=2021|title=Five carbon- and nitrogen-bearing species in a hot giant planet's atmosphere|bibcode=2021Natur.592..205G|last1=Giacobbe|first1=Paolo|last2=Brogi|first2=Matteo|last3=Gandhi|first3=Siddharth|last4=Cubillos|first4=Patricio E.|last5=Bonomo|first5=Aldo S.|last6=Sozzetti|first6=Alessandro|last7=Fossati|first7=Luca|last8=Guilluy|first8=Gloria|last9=Carleo|first9=Ilaria|last10=Rainer|first10=Monica|last11=Harutyunyan|first11=Avet|last12=Borsa|first12=Francesco|last13=Pino|first13=Lorenzo|last14=Nascimbeni|first14=Valerio|last15=Benatti|first15=Serena|last16=Biazzo|first16=Katia|last17=Bignamini|first17=Andrea|last18=Chubb|first18=Katy L.|last19=Claudi|first19=Riccardo|last20=Cosentino|first20=Rosario|last21=Covino|first21=Elvira|last22=Damasso|first22=Mario|last23=Desidera|first23=Silvano|last24=Fiorenzano|first24=Aldo F. M.|last25=Ghedina|first25=Adriano|last26=Lanza|first26=Antonino F.|last27=Leto|first27=Giuseppe|last28=Maggio|first28=Antonio|last29=Malavolta|first29=Luca|last30=Maldonado|first30=Jesus|journal=Nature|volume=592|issue=7853|pages=205–208 |doi=10.1038/s41586-021-03381-x|pmid=33828321 |s2cid=233181895|display-authors=1}}

In 2014, a magnetic field around HD 209458 b was inferred from the way hydrogen was evaporating from the planet. It is the first (indirect) detection of a magnetic field on an exoplanet. The magnetic field is estimated to be about one tenth as strong as Jupiter's.[http://www.space.com/27828-alien-planet-magnetic-field-strength.html Unlocking the Secrets of an Alien World's Magnetic Field], Space.com, by Charles Q. Choi, November 20, 2014{{Cite journal|doi=10.1126/science.1257829 |pmid=25414310 |title=Magnetic moment and plasma environment of HD 209458b as determined from Ly observations |journal=Science |volume=346 |issue=6212 |pages=981–4 |year=2014 |last1=Kislyakova |first1=K. G. |last2=Holmstrom |first2=M. |last3=Lammer |first3=H. |last4=Odert |first4=P. |last5=Khodachenko |first5=M. L. |bibcode=2014Sci...346..981K |arxiv = 1411.6875 |s2cid=206560188 }}

Since HD 209458 b orbits less than 0.1 AU from its host star, theorists hypothesized that it may cause stellar flaring synchronized to the orbital period of the exoplanet. A 2011 search for these magnetic star-planet interactions that would result in coronal radio emissions did not detect any signal. Similarly, no magnetospheric radio emissions were detected from the planet either.{{cite journal|last1=Route|first1=Matthew|last2=Wolszczan|first2=Alex|title=ROME. III. The Arecibo Search for Star–Planet Interactions at 5 GHz|journal=The Astrophysical Journal|date=1 August 2023|volume=952|issue=2|page=118|doi=10.3847/1538-4357/acd9ad|arxiv=2202.08899|bibcode=2023ApJ...952..118R|doi-access=free }}

File:Clear to cloudy hot Jupiters.jpg" exoplanets (artist concept).}}
From top left to lower right: WASP-12b, WASP-6b, WASP-31b, WASP-39b, HD 189733b, HAT-P-12b, WASP-17b, WASP-19b, HAT-P-1b and HD 209458b.]]

• 51 Pegasi b
• YZ Ceti another extra solar planet with evidence of magnetic fields
• HAT-P-11b another extra solar planet with evidence of magnetic fields
• Tau Boötis b another extra solar planet with evidence of magnetic fields
• List of exoplanets discovered before 2000

{{reflist|refs=

[http://www.space.com/scienceastronomy/070410_water_exoplanet.html Water Found in Extrasolar Planet's Atmosphere] – Space.com

{{cite web |title=Hubble Traces Subtle Signals of Water on Hazy Worlds |url=http://www.nasa.gov/content/goddard/hubble-traces-subtle-signals-of-water-on-hazy-worlds/ |date=December 3, 2013 |publisher=NASA |access-date=December 4, 2013}}

{{cite journal |title=Infrared Transmission Spectroscopy of the Exoplanets HD 209458b and XO-1b Using the Wide Field Camera-3 on the Hubble Space Telescope |date=September 10, 2013 |journal=Astrophysical Journal |volume=774 |issue=2 |page=95 |doi=10.1088/0004-637X/774/2/95 |arxiv = 1302.1141 |bibcode = 2013ApJ...774...95D |display-authors=1 |last1=Deming |first1=Drake |first2=Ashlee |last3=McCullough |last2 = Mccullough|first3=Peter |last4=Burrows |first4=Adam |last5=Fortney |first5=Jonathan J. |last6=Agol |first6=Eric |last7=Dobbs-Dixon |first7=Ian |last8=Madhusudhan |first8=Nikku |last9=Crouzet |first9=Nicolas |last10=Desert |first10=Jean-Michel |last11=Gilliland |first11=Ronald L. |last12=Haynes |first12=Korey |last13=Knutson |first13=Heather A. |last14=Line |first14=Michael |last15=Magic |first15=Zazralt |last16=Mandell |first16=Avi M. |last17=Ranjan |first17=Sukrit |last18=Charbonneau |first18=David |last19=Clampin |first19=Mark |last20=Seager |first20=Sara |last21=Showman |first21=Adam P. |s2cid=10960488 |author-link2=Peter Mccullough }}

{{cite web |last1=Harrington |first1=J.D. |last2=Villard |first2=Ray |title=RELEASE 14-197 – Hubble Finds Three Surprisingly Dry Exoplanets |url=http://www.nasa.gov/press/2014/july/hubble-finds-three-surprisingly-dry-exoplanets/

|date=July 24, 2014 |work=NASA |access-date=July 25, 2014 }}

Henry et al. [http://cbat.eps.harvard.edu/iauc/07300/07307.html#Item1 IAUC 7307: HD 209458; SAX J1752.3-3138] 12 November 1999, reported a transit ingress on Nov. 8. David Charbonneau et al., [http://www.iop.org/EJ/article/1538-4357/529/1/L45/995832.html Detection of Planetary Transits Across a Sun-like Star], November 19, reports full transit observations on September 9 and 16.

{{cite journal |last1=Charbonneau |first1=David |last2=Brown |first2=Timothy M. |last3=Latham |first3=David W. |last4=Mayor |first4=Michel |date=January 2000 |title=Detection of Planetary Transits Across a Sun-like Star |journal=The Astrophysical Journal |volume=529 |issue=1 |pages=L45–L48 |doi=10.1086/312457 |pmid=10615033 |arxiv=astro-ph/9911436 |bibcode=2000ApJ...529L..45C}}

{{cite journal |last1=Henry |first1=Gregory W. |last2=Marcy |first2=Geoffrey W. |last3=Butler |first3=R. Paul |last4=Vogt |first4=Steven S. |date=January 2000 |title=A Transiting "51 Peg-like" Planet |journal=The Astrophysical Journal |volume=529 |issue=1 |pages=L41–L44 |doi=10.1086/312458 |bibcode=2000ApJ...529L..41H|doi-access=free |pmid=10615032 }}

{{Cite encyclopedia|url=https://exoplanet.eu/catalog/?f=%27HD%20209458%27+in+name/|encyclopedia=Extrasolar Planets Encyclopaedia|title=The Extrasolar Planet Encyclopaedia — Catalog Listing|date=1995 }}

{{cite journal |last1=Richardson |first1=L. Jeremy |display-authors=etal |date=2007 |title=A spectrum of an extrasolar planet |journal=Nature |volume=445 |issue=7130 |pages=892–895 |doi=10.1038/nature05636 |pmid=17314975 |arxiv = astro-ph/0702507 |bibcode = 2007Natur.445..892R |last2=Deming |first2=D |last3=Horning |first3=K |last4=Seager |first4=S |last5=Harrington |first5=J |s2cid=4415500 }}

{{cite journal|author=Ignas A. G. Snellen|display-authors=etal|date=2010|title=The orbital motion, absolute mass and high-altitude winds of exoplanet HD 209458b|journal=Nature|pmid=20577209|volume=465|issue=7301|pages=1049–1051|doi=10.1038/nature09111|bibcode = 2010Natur.465.1049S |arxiv = 1006.4364 |last2=De Kok|last3=De Mooij|last4=Albrecht|s2cid=205220901}}

{{cite journal | journal=Astronomy & Astrophysics |volume=485 | issue=3|pages= 865–869 |date=2008| title=Rayleigh scattering by H in the extrasolar planet HD 209458b |author1=A. Lecavelier des Etangs |author2=A. Vidal-Madjar |author3=J.-M. Désert |author4=D. Sing |doi=10.1051/0004-6361:200809704 | bibcode=2008A&A...485..865L|arxiv = 0805.0595 |s2cid=18700671 }}

Matthews J., (2005), [http://www.astro.umontreal.ca/~casca/PR/Casca2005_Matthews.html MOST Space Telescope Plays 'Hide & Seek' With an Exoplanet; Learns About Atmosphere and Weather of a Distant World] {{Webarchive|url=https://web.archive.org/web/20090709055449/http://www.astro.umontreal.ca/~casca/PR/Casca2005_Matthews.html |date=2009-07-09 }}

{{Cite journal |arxiv=0807.3588|doi=10.1017/S1743921308026458|title=Spectrum and atmosphere models of irradiated transiting giant planets|journal=Proceedings of the International Astronomical Union|volume=4|pages=239–245|year=2009|last1=Hubeny|first1=Ivan|last2=Burrows|first2=Adam|bibcode=2009IAUS..253..239H|s2cid=13978248}}

{{Cite journal| arxiv=0807.4541 |doi=10.1017/S1743921308026495|title=Radiative Hydrodynamical Studies of Irradiated Atmospheres|journal=Proceedings of the International Astronomical Union|volume=4|pages=273–279|year=2009|last1=Dobbs-Dixon|first1=Ian|bibcode=2009IAUS..253..273D|s2cid=118643167}}

{{cite journal|arxiv=astro-ph/0312384|last1= Hébrard|first1= G.|title= Evaporation rate of hot Jupiters and formation of Chthonian planets|journal= Extrasolar Planets: Today and Tomorrow|pages= 203–204|last2= Lecavelier des Étangs|first2= A.|last3= Vidal-Madjar|first3= A.|last4= Désert|first4= J. -M.|last5= Ferlet|first5= R.|year= 2003|bibcode=2004ASPC..321..203H|isbn=978-1-58381-183-2|series=ASP Conference Proceedings|volume= 321|editor1=Jean-Philippe Beaulieu |editor2=Alain Lecavelier des Étangs |editor3=Caroline Terquem|id=30 June – 4 July 2003, Institut d'astrophysique de Paris, France}}

{{cite journal | url=http://www.iop.org/EJ/article/1538-4357/661/2/L191/21561.html | author=Barman | title=Identification of Absorption Features in an Extrasolar Planet Atmosphere | journal=The Astrophysical Journal Letters | volume=661 | issue=2 | date=2007 | pages=L191–L194 | doi=10.1086/518736 | bibcode=2007ApJ...661L.191B|arxiv = 0704.1114 | s2cid=13964464 }}

{{cite journal |last1=Zellem |first1=Robert T. |last2=Lewis |first2=Nikole K. |display-authors=etal |date=July 2014 |title=The 4.5 μm Full-orbit Phase Curve of the Hot Jupiter HD 209458b |journal=The Astrophysical Journal |volume=790 |issue=1 |page=53 |doi=10.1088/0004-637X/790/1/53 |arxiv=1405.5923 |bibcode=2014ApJ...790...53Z}}

{{cite journal |last1=Bonomo |first1=A. S. |last2=Desidera |first2=S. |display-authors=etal |date=June 2017 |title=The GAPS Programme with HARPS-N at TNG. XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets |journal=Astronomy & Astrophysics |volume=602 |issue= |pages=A107 |doi=10.1051/0004-6361/201629882 |arxiv=1704.00373 |bibcode=2017A&A...602A.107B}}

{{cite journal |last1=Brandeker |first1=A. |last2=Heng |first2=K. |display-authors=etal |date=March 2022 |title=CHEOPS geometric albedo of the hot Jupiter HD 209458 b |journal=Astronomy & Astrophysics |volume=659 |issue= |pages=L4 |doi=10.1051/0004-6361/202243082 |arxiv=2202.11516 |bibcode=2022A&A...659L...4B}}

{{cite conference |title="Osiris" (HD209458b), an Evaporating Planet |last1=Vidal-Madjar |first1=A. |last2=Lecavelier des Etangs |first2=A. |date=December 2004 |publisher=ASP Conference Proceedings |page=152 |location=Institut D'Astrophysique de Paris, France |conference=Extrasolar Planets: Today and Tomorrow |bibcode=2004ASPC..321..152V |arxiv=astro-ph/0312382 |isbn=1-58381-183-4}}

{{cite journal |last1=Vidal-Madjar |first1=A. |last2=Lecavelier des Etangs |first2=A. |display-authors=etal |date=March 2008 |title=Exoplanet HD 209458b (Osiris): Evaporation Strengthened |journal=The Astrophysical Journal Letters |volume=676 |issue=1 |pages=L57 |doi=10.1086/587036 |arxiv=0802.0587 |bibcode=2008ApJ...676L..57V}}

{{cite web |url=https://www.iau.org/public/themes/naming_exoplanets/ |title=Naming of exoplanets |publisher=IAU |access-date=1 August 2023}}

}}

{{Refbegin}}

• {{Cite book |author-link=David Charbonneau |last=Charbonneau |first=D. |date=2003 |chapter=HD 209458 and the Power of the Dark Side |title=Scientific Frontiers in Research on Extrasolar Planets |series=ASP Conference Series |volume=294 |editor1-first=Drake |editor1-last=Deming |editor2-first=Sara |editor2-last=Seager |location=San Francisco |publisher=ASP |isbn=978-1-58381-141-2 |pages=449–456}}.
• {{Cite journal |first1=Drake |last1=Deming |first2=Sara |last2=Seager |first3=L. Jeremy |last3=Richardson |name-list-style=amp |first4=Joseph |last4=Harrington |title=Infrared radiation from an extrasolar planet |journal=Nature |volume=434 |issue=7034 |pages=740–743 |date=2005 |doi=10.1038/nature03507 |pmid=15785769 |arxiv = astro-ph/0503554 |bibcode = 2005Natur.434..740D |s2cid=4404769 }}.
• {{Cite journal |last1=Fortney |first1=J. J. |last2=Sudarsky |first2=D. |last3=Hubeny |first3=I. |last4=Cooper |first4=C. S. |last5=Hubbard |first5=W. B. |last6=Burrows |first6=A. |last7=Lunine |first7=Jonathan I. |date=2003 |title=On the Indirect Detection of Sodium in the Atmosphere of the Planetary Companion to HD 209458 |journal=Astrophysical Journal |volume=589 |issue=1 |doi=10.1086/374387 |pages=615–622 |bibcode=2003ApJ...589..615F|arxiv = astro-ph/0208263 |s2cid=14028421 }}.
• {{Cite journal |first1=M. |last1=Holmström |first2=A. |last2=Ekenbäck |first3=F. |last3=Selsis |first4=T. |last4=Penz |first5=H. |last5=Lammer |name-list-style=amp |first6=P. |last6=Wurz |title=Energetic neutral atoms as the explanation for the high-velocity hydrogen around HD 209458b |journal=Nature |volume=451 |issue=7181 |pages=970–972 |date=2008 |doi=10.1038/nature06600 |pmid=18288189 |bibcode = 2008Natur.451..970H |arxiv = 0802.2764 |s2cid=15426903 }}.

{{Refend}}

{{Commons category|HD 209458 b}}

• {{cite web |url=http://www.spacetelescope.org/news/html/heic0303.html |title=European astronomers observe first evaporating planet |access-date=2008-06-28 |work=Hubble Space Telescope |publisher=ESA/NASA |date=2003-03-12 |archive-date=2008-07-07 |archive-url=https://web.archive.org/web/20080707002649/http://www.spacetelescope.org/news/html/heic0303.html |url-status=dead }}
• [https://www.nasa.gov/press/2014/july/hubble-finds-three-surprisingly-dry-exoplanets/ Hubble Finds Three Surprisingly Dry Exoplanets]
• {{cite web |url=https://www.newscientist.com/article.ns?id=dn7186 |title=Glow of alien planets glimpsed at last |access-date=2008-06-28 |work=NewScientist |date=2005-03-22 |first=Jenny |last=Hogan }}
• {{cite web |url=http://hubblesite.org/newscenter/archive/releases/2001/38/text |title=Hubble Makes First Direct Measurements of Atmosphere on World Around another Star |access-date=2008-06-28 |work=Hubble Space Telescope |publisher=NASA |date=2001-11-27 }}
• {{cite web |url=https://www.newscientist.com/article.ns?id=dn4634 |title=Oxygen seen streaming off exoplanet |access-date=2008-06-28 |work=NewScientist |date=2004-02-03 |first=Maggie |last=McKee }}
• {{cite web |url=http://www.jpl.nasa.gov/news/news.cfm?release=2005-050 |title=NASA's Spitzer Marks Beginning of New Age of Planetary Science |access-date=2008-06-28 |work=Jet Propulsion Laboratory |publisher=NASA |date=2005-03-22 |archive-date=2008-09-21 |archive-url=https://web.archive.org/web/20080921132238/http://www.jpl.nasa.gov/news/news.cfm?release=2005-050 }}
• {{cite web |url=http://www.spacetelescope.org/news/html/heic0403.html |title=Oxygen and carbon discovered in exoplanet atmosphere 'blow-off' |access-date=2008-06-28 |work=Hubble Space Telescope |publisher=ESA/NASA |date=2004-02-02 |archive-date=2009-04-27 |archive-url=https://web.archive.org/web/20090427160731/http://www.spacetelescope.org/news/html/heic0403.html |url-status=dead }}
• {{cite journal |url=http://www.nature.com/news/2005/050321/full/news050321-9.html |title=Light from alien planets confirmed |access-date=2008-06-28 |journal=Nature |date=2005-03-23 |first=Mark |last=Peplow |pages=news050321–9 |doi=10.1038/news050321-9 |url-access=subscription }}
• [http://www.aavso.org/vstar/vsots/fall04.shtml AAVSO Variable Star Of The Season. Fall 2004: The Transiting Exoplanets HD 209458 and TrES-1] {{Webarchive|url=https://web.archive.org/web/20041028011426/http://www.aavso.org/vstar/vsots/fall04.shtml |date=2004-10-28 }}

{{Sky|22|03|10.8||18|53|04|154}}

{{Pegasus (constellation)}}

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Category:Exoplanets discovered in 1999

Category:Giant planets

Category:Hot Jupiters

Category:Pegasus (constellation)

Category:Transiting exoplanets

Category:Exoplanets detected by radial velocity

Category:Exoplanets with proper names