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<!-- ORBITAL -->
<!-- ORBITAL -->
| apsis = astron
| apsis = astron
| semimajor = {{val|0.03462|0.00110|0.00093}} [[astronomical unit|AU]]
| semimajor = {{val|0.03462}}{{±|0.00110|0.00093}} [[astronomical unit|AU]]
| period = 1.4811235{{±|0.0000011}}<ref name=scottgaudi/> [[day|d]]
| period = 1.4811235{{±|0.0000011}}<ref name=scottgaudi/> [[day|d]]
| inclination = {{val|86.79|0.25}}<ref name=scottgaudi/>
| inclination = {{val|86.79|0.25}}<ref name=scottgaudi/>
| star = [[HD 195689]]
| star = [[HD 195689]]
<!-- PHYS CHARS -->
<!-- PHYS CHARS -->
| mean_radius = {{val|1.891|0.061|0.053}}<ref name=scottgaudi/> {{Jupiter radius|link=y}}
| mean_radius = {{val|1.891}}{{±|0.061|0.053}}<ref name=scottgaudi/> {{Jupiter radius|link=y}}
| mass = 2.17{{±|0.56}}<ref name="Asnodkar2022"/> {{Jupiter mass|link=y}}
| mass = 2.17{{±|0.56}}<ref name="Asnodkar2022"/> {{Jupiter mass|link=y}}
| density = {{val|530|0.15}} [[kilogram|kg]] [[cubic metre|m<sup>−3</sup>]]
| density = {{cvt|530|±|0.15|kg/m3|g/cm3|disp=out}}{{fact|date=July 2024}}
| single_temperature = {{val|4050|180}}<ref name=scottgaudi/> [[Kelvin|K]]
| single_temperature = {{val|4050|180}}<ref name=scottgaudi/> [[Kelvin|K]]
| albedo = <0.007<ref name=Jones2022/>
| albedo = <0.14<ref name=Jones2022/>
<!-- ATMOSPHERE -->
<!-- ATMOSPHERE -->
<!-- NOTES -->
<!-- NOTES -->
}}
}}
'''KELT-9b''' is an [[exoplanet]] and [[Hot Jupiter#Ultra-hot Jupiters|ultra-hot Jupiter]] that orbits the late [[B-type main-sequence star|B-type]]/early [[A-type main-sequence star|A-type star]] KELT-9,<ref name="NASA-20200124">{{cite news |last1=Brennan |first1=Pat |last2=Cofield |first2=Calia |title=For Hottest Planet, a Major Meltdown, Study Shows |url=https://www.jpl.nasa.gov/news/news.php?feature=7583 |date=24 January 2020 |work=[[NASA]] |access-date=24 January 2020 }}</ref> located about 670 [[light-year]]s from [[Earth]].<ref name="NASA-20200124" /> Detected using the [[Kilodegree Extremely Little Telescope]], the discovery of KELT-9b was announced in 2016.<ref name=collins/><ref name=scottgaudi/> {{As of|2022|Oct}}, it is the hottest known exoplanet.<ref>{{Cite web |last=Tribur |first=Melissa |date=2017-06-05 |title=Meet KELT-9b, the Hottest Exoplanet Ever Discovered |url=http://eos.org/articles/meet-kelt-9b-the-hottest-exoplanet-ever-discovered |access-date=2022-10-28 |website=Eos |language=en-US}}</ref>
'''KELT-9b''' is an [[exoplanet]] and [[Hot Jupiter#Ultra-hot Jupiters|ultra-hot Jupiter]] that orbits the late [[B-type main-sequence star|B-type]]/early [[A-type main-sequence star|A-type star]] KELT-9,<ref name="NASA-20200124">{{cite news |last1=Brennan |first1=Pat |last2=Cofield |first2=Calia |title=For Hottest Planet, a Major Meltdown, Study Shows |url=https://www.jpl.nasa.gov/news/news.php?feature=7583 |date=24 January 2020 |work=[[NASA]] |access-date=24 January 2020 }}</ref> located about 670 [[light-year]]s from [[Earth]].<ref name="NASA-20200124" /> Detected using the [[Kilodegree Extremely Little Telescope]], the discovery of KELT-9b was announced in 2016.<ref name=collins/><ref name=scottgaudi/> As of June 2017, it is the hottest known exoplanet.<ref>{{Cite web |last=Tribur |first=Melissa |date=2017-06-05 |title=Meet KELT-9b, the Hottest Exoplanet Ever Discovered |url=http://eos.org/articles/meet-kelt-9b-the-hottest-exoplanet-ever-discovered |access-date=2022-10-28 |website=Eos |language=en-US}}</ref>


== Host star ==
== Host star ==
The host [[star]], '''KELT-9''', is 2 to 3 times larger and 2 to 5 times more massive than the sun. The surface temperature is {{convert|10170|K|C F|0|lk=on|abbr=on}}, unusually hot for a star with a [[transit (astronomy)|transit]]ing planet. Prior to the discovery of KELT-9b, only six A-type stars were known to have planets, of which the warmest, [[WASP-33]], is significantly cooler at {{convert|7430|K|C F|0|abbr=on}}; no B-type stars were previously known to host planets. KELT-9, classified as B9.5-A0<ref name=scottgaudi/><ref name=mk/> could be the first B-type star known to have a planet. KELT-9b occupies a circular but strongly [[orbital inclination|inclined]] orbit a mere 0.03462 [[astronomical unit|AU]] from KELT-9 with an [[orbital period]] of less than 1.5 [[day]]s.<ref name=autogenerated1>[https://exoplanets.nasa.gov/exoplanet-catalog/3508/kelt-9-b/ KELT-9 b] Exoplanet Exploration Program 2017</ref><ref name="jpl,7june2017" />
The host [[star]], '''KELT-9''', is 2 to 3 times larger and 2 to 3 times more massive than the sun. The surface temperature is {{convert|10170|K|C F|0|lk=on|abbr=on}}, unusually hot for a star with a [[transit (astronomy)|transit]]ing planet. Prior to the discovery of KELT-9b, only six A-type stars were known to have planets, of which the warmest, [[WASP-33]], is significantly cooler at {{convert|7430|K|C F|0|abbr=on}}; no B-type stars were previously known to host planets. KELT-9, classified as B9.5-A0<ref name=scottgaudi/><ref name=mk/> could be the first B-type star known to have a planet. KELT-9b occupies a circular but strongly [[orbital inclination|inclined]] orbit a mere 0.03462 [[astronomical unit|AU]] from KELT-9 with an [[orbital period]] of less than 1.5 [[day]]s.<ref name=autogenerated1>[https://exoplanets.nasa.gov/exoplanet-catalog/3508/kelt-9-b/ KELT-9 b] Exoplanet Exploration Program 2017</ref><ref name="jpl,7june2017" />


== Physical properties ==
== Physical properties ==
[[File:PIA21472-16-KELT9b-20200124.gif|thumb|left|150px|<div align="center">Exoplanet KELT-9b orbits host star KELT-9</div>]]
[[File:PIA21472 - Hottest Hot Jupiter Animation (Artist's Concept).gif|thumb|left|150px|<div align="center">Exoplanet KELT-9b orbits host star KELT-9</div>]]
KELT-9b is a relatively large [[giant planet]] at about 2.8 times [[Jupiter mass|the mass]] of [[Jupiter]]; however given that its radius is nearly twice that of Jupiter, its density is less than half that of it. Like many [[hot Jupiter]]s, KELT-9b is [[Tidal locking|tidally locked]] with its host star.<ref name=jpl,7june2017>[https://www.jpl.nasa.gov/news/news.php?feature=6865 NASA JPL, Pasadena CA (5 June 2017) Astronomers Find Planet Hotter Than Most Stars]</ref>
KELT-9b is a relatively large [[giant planet]] at about 2.8 times [[Jupiter mass|the mass]] of [[Jupiter]]; however given that its radius is nearly twice that of Jupiter, its density is less than half that of it. Like many [[hot Jupiter]]s, KELT-9b is [[Tidal locking|tidally locked]] with its host star.<ref name=jpl,7june2017>[https://www.jpl.nasa.gov/news/news.php?feature=6865 NASA JPL, Pasadena CA (5 June 2017) Astronomers Find Planet Hotter Than Most Stars]</ref>
The outer boundary of its atmosphere nearly reaches its [[Roche lobe]], implying that the planet is experiencing rapid [[atmospheric escape]]<ref name=yan2018/> driven by the extreme amount of radiation it receives from its host star.<ref name="jpl,7june2017" /><ref name=autogenerated1 /> In 2020, atmospheric loss rate was measured to be equal to 18 - 68 Earth masses per billion years.<ref>{{cite journal|arxiv=2004.13733|last1=Wyttenbach|first1=A.|last2=Mollière|first2=P.|last3=Ehrenreich|first3=D.|last4=Cegla|first4=H. M.|last5=Bourrier|first5=V.|last6=Lovis|first6=C.|last7=Pino|first7=L.|last8=Allart|first8=R.|last9=Seidel|first9=J. V.|last10=Hoeijmakers|first10=H. J.|last11=Nielsen|first11=L. D.|last12=Lavie|first12=B.|last13=Pepe|first13=F.|last14=Bonfils|first14=X.|last15=Snellen|first15=I. A. G.|title=Mass loss rate and local thermodynamic state of KELT-9 b thermosphere from the hydrogen Balmer series|journal=Astronomy & Astrophysics|year=2020|volume=638|pages=A87|doi=10.1051/0004-6361/201937316|bibcode=2020A&A...638A..87W|s2cid=216641961}}</ref>
The outer boundary of its atmosphere nearly reaches its [[Roche lobe]], implying that the planet is experiencing rapid [[atmospheric escape]]<ref name=yan2018/> driven by the extreme amount of radiation it receives from its host star.<ref name="jpl,7june2017" /><ref name=autogenerated1 /> In 2020, atmospheric loss rate was measured to be equal to 18 - 68 Earth masses per billion years.<ref>{{cite journal|arxiv=2004.13733|last1=Wyttenbach|first1=A.|last2=Mollière|first2=P.|last3=Ehrenreich|first3=D.|last4=Cegla|first4=H. M.|last5=Bourrier|first5=V.|last6=Lovis|first6=C.|last7=Pino|first7=L.|last8=Allart|first8=R.|last9=Seidel|first9=J. V.|last10=Hoeijmakers|first10=H. J.|last11=Nielsen|first11=L. D.|last12=Lavie|first12=B.|last13=Pepe|first13=F.|last14=Bonfils|first14=X.|last15=Snellen|first15=I. A. G.|title=Mass loss rate and local thermodynamic state of KELT-9 b thermosphere from the hydrogen Balmer series|journal=Astronomy & Astrophysics|year=2020|volume=638|pages=A87|doi=10.1051/0004-6361/201937316|bibcode=2020A&A...638A..87W|s2cid=216641961}}</ref>
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[[File:Temperature vs Mass of known exoplanets.png|thumb|This graph shows the average temperature and mass relative to Jupiter (Mj) of known exoplanets as of 2022]]
[[File:Temperature vs Mass of known exoplanets.png|thumb|This graph shows the average temperature and mass relative to Jupiter (Mj) of known exoplanets as of 2022]]


{{As of|2022}}, KELT-9b is the hottest known exoplanet, with a dayside temperatures approaching {{convert|4600|K|C F|0|abbr=on}} — warmer than some [[K-type main-sequence star|K-type stars]].<ref name=scottgaudi/><ref name=NASA-20200124/> Molecules on the day side are broken into their component atoms, so that normally sequestered [[heavy metals|refractory element]]s can exist as [[atom|atomic species]], including neutral [[oxygen]],<ref>{{citation|arxiv=2112.12059|year=2022|title=High-resolution detection of neutral oxygen and non-LTE effects in the atmosphere of KELT-9b|doi=10.1038/s41550-021-01544-4|last1=Borsa|first1=Francesco|last2=Fossati|first2=Luca|last3=Koskinen|first3=Tommi|last4=Young|first4=Mitchell E.|last5=Shulyak|first5=Denis|journal=Nature Astronomy|volume=6|issue=2|pages=226–231|s2cid=245385802}}</ref> neutral and singly [[ionization|ionize]]d atomic [[iron]]<ref>{{cite journal|arxiv=2004.11335|last1=Pino|first1=L.|last2=Désert|first2=J. M.|last3=Brogi|first3=M.|last4=Malavolta|first4=L.|last5=Wyttenbach|first5=A.|last6=Line|first6=M.|last7=Hoeijmakers|first7=J.|last8=Fossati|first8=L.|last9=Bonomo|first9=A. S.|last10=Nascimbeni|first10=V.|last11=Panwar|first11=V.|last12=Affer|first12=L.|last13=Benatti|first13=S.|last14=Biazzo|first14=K.|last15=Bignamini|first15=A.|last16=Borsa|first16=F.|last17=Carleo|first17=I.|last18=Claudi|first18=R.|last19=Cosentino|first19=R.|last20=Covino|first20=E.|last21=Damasso|first21=M.|last22=Desidera|first22=S.|last23=Giacobbe|first23=P.|last24=Harutyunyan|first24=A.|last25=Lanza|first25=A. F.|last26=Leto|first26=G.|last27=Maggio|first27=A.|last28=Maldonado|first28=J.|last29=Mancini|first29=L.|last30=Micela|first30=G.|title=Neutral Iron Emission Lines from the Day-side of KELT-9b -- the GAPS Programme with HARPS-N at TNG XX|journal=The Astrophysical Journal|year=2020|volume=894|issue=2|pages=L27|doi=10.3847/2041-8213/ab8c44|bibcode=2020ApJ...894L..27P|s2cid=216080480|display-authors=29 |doi-access=free }}</ref> (Fe and Fe<sup>+</sup>) and singly ionized [[titanium]] (Ti<sup>+</sup>),<ref name=Hoeijmakers+2018/> only to temporarily reform once they reach the cooler night side,<ref name=NASA-20200124/> which is indirectly confirmed by measured enhanced heat transfer efficiency of 0.3 between dayside and nightside, likely diven by the latent heat of dissociation and recombination of the molecular hydrogen.<ref name=Jones2022>{{citation|arxiv=2208.04818|year=2022|title=The stable climate of KELT-9b|doi=10.1051/0004-6361/202243823 |last1=Jones |first1=K. |last2=Morris |first2=B. M. |last3=Demory |first3=B.-O. |last4=Heng |first4=K. |last5=Hooton |first5=M. J. |last6=Billot |first6=N. |last7=Ehrenreich |first7=D. |last8=Hoyer |first8=S. |last9=Simon |first9=A. E. |last10=Lendl |first10=M. |last11=Demangeon |first11=O. D. S. |last12=Sousa |first12=S. G. |last13=Bonfanti |first13=A. |last14=Wilson |first14=T. G. |last15=Salmon |first15=S. |last16=Csizmadia |first16=Sz. |last17=Parviainen |first17=H. |last18=Bruno |first18=G. |last19=Alibert |first19=Y. |last20=Alonso |first20=R. |last21=Anglada |first21=G. |last22=Bárczy |first22=T. |last23=Barrado |first23=D. |last24=Barros |first24=S. C. C. |last25=Baumjohann |first25=W. |last26=Beck |first26=M. |last27=Beck |first27=T. |last28=Benz |first28=W. |last29=Bonfils |first29=X. |last30=Brandeker |first30=A. |journal=Astronomy & Astrophysics |volume=666 |pages=A118 |bibcode=2022A&A...666A.118J |s2cid=251442580 |display-authors=1 }}</ref> Surprisingly, spectra taken in 2021 have unambiguously indicated a presence of metal oxides and hydrides in the planetary atmosphere,<ref>{{citation|arxiv=2101.00469|title=The Hubble WFC3 Emission Spectrum of the Extremely Hot Jupiter KELT-9b|year=2021|last1=Changeat|first1=Quentin|last2=Edwards|first2=Billy|journal=The Astrophysical Journal Letters|volume=907|issue=1|pages=L22|doi=10.3847/2041-8213/abd84f|bibcode=2021ApJ...907L..22C|s2cid=230435556 |doi-access=free }}</ref> although higher resolution spectra taken in 2021 have not found any molecular emissions from the planetary dayside.<ref>{{citation|arxiv=2108.08389|year=2021|title=Confirmation of Iron Emission Lines and Nondetection of TiO on the Dayside of KELT-9b with MAROON-X|doi=10.3847/2041-8213/ac30e1|last1=Kasper|first1=David|last2=Bean|first2=Jacob L.|last3=Line|first3=Michael R.|last4=Seifahrt|first4=Andreas|last5=Stürmer|first5=Julian|last6=Pino|first6=Lorenzo|last7=Désert|first7=Jean-Michel|last8=Brogi|first8=Matteo|journal=The Astrophysical Journal Letters|volume=921|issue=1|pages=L18|bibcode=2021ApJ...921L..18K|s2cid=239024467 |doi-access=free }}</ref>
{{As of|2022}}, KELT-9b is the hottest known exoplanet, with dayside temperatures approaching {{convert|4600|K|C F|0|abbr=on}} — warmer than some [[K-type main-sequence star|K-type stars]].<ref name=scottgaudi/><ref name=NASA-20200124/> Molecules on the day side are broken into their component atoms, so that normally sequestered [[heavy metals|refractory element]]s can exist as [[atom|atomic species]], including neutral [[oxygen]],<ref>{{citation|arxiv=2112.12059|year=2022|title=High-resolution detection of neutral oxygen and non-LTE effects in the atmosphere of KELT-9b|doi=10.1038/s41550-021-01544-4|last1=Borsa|first1=Francesco|last2=Fossati|first2=Luca|last3=Koskinen|first3=Tommi|last4=Young|first4=Mitchell E.|last5=Shulyak|first5=Denis|journal=Nature Astronomy|volume=6|issue=2|pages=226–231|s2cid=245385802}}</ref> neutral and singly [[ionization|ionize]]d atomic [[iron]]<ref>{{cite journal|arxiv=2004.11335|last1=Pino|first1=L.|last2=Désert|first2=J. M.|last3=Brogi|first3=M.|last4=Malavolta|first4=L.|last5=Wyttenbach|first5=A.|last6=Line|first6=M.|last7=Hoeijmakers|first7=J.|last8=Fossati|first8=L.|last9=Bonomo|first9=A. S.|last10=Nascimbeni|first10=V.|last11=Panwar|first11=V.|last12=Affer|first12=L.|last13=Benatti|first13=S.|last14=Biazzo|first14=K.|last15=Bignamini|first15=A.|last16=Borsa|first16=F.|last17=Carleo|first17=I.|last18=Claudi|first18=R.|last19=Cosentino|first19=R.|last20=Covino|first20=E.|last21=Damasso|first21=M.|last22=Desidera|first22=S.|last23=Giacobbe|first23=P.|last24=Harutyunyan|first24=A.|last25=Lanza|first25=A. F.|last26=Leto|first26=G.|last27=Maggio|first27=A.|last28=Maldonado|first28=J.|last29=Mancini|first29=L.|last30=Micela|first30=G.|title=Neutral Iron Emission Lines from the Day-side of KELT-9b -- the GAPS Programme with HARPS-N at TNG XX|journal=The Astrophysical Journal|year=2020|volume=894|issue=2|pages=L27|doi=10.3847/2041-8213/ab8c44|bibcode=2020ApJ...894L..27P|s2cid=216080480|display-authors=29 |doi-access=free }}</ref> (Fe and Fe<sup>+</sup>) and singly ionized [[titanium]] (Ti<sup>+</sup>),<ref name=Hoeijmakers+2018/> only to temporarily reform once they reach the cooler night side,<ref name=NASA-20200124/> which is indirectly confirmed by measured enhanced heat transfer efficiency of 0.3 between dayside and nightside, likely diven by the latent heat of dissociation and recombination of the molecular hydrogen.<ref name=Jones2022>{{citation|arxiv=2208.04818|year=2022|title=The stable climate of KELT-9b|doi=10.1051/0004-6361/202243823 |last1=Jones |first1=K. |last2=Morris |first2=B. M. |last3=Demory |first3=B.-O. |last4=Heng |first4=K. |last5=Hooton |first5=M. J. |last6=Billot |first6=N. |last7=Ehrenreich |first7=D. |last8=Hoyer |first8=S. |last9=Simon |first9=A. E. |last10=Lendl |first10=M. |last11=Demangeon |first11=O. D. S. |last12=Sousa |first12=S. G. |last13=Bonfanti |first13=A. |last14=Wilson |first14=T. G. |last15=Salmon |first15=S. |last16=Csizmadia |first16=Sz. |last17=Parviainen |first17=H. |last18=Bruno |first18=G. |last19=Alibert |first19=Y. |last20=Alonso |first20=R. |last21=Anglada |first21=G. |last22=Bárczy |first22=T. |last23=Barrado |first23=D. |last24=Barros |first24=S. C. C. |last25=Baumjohann |first25=W. |last26=Beck |first26=M. |last27=Beck |first27=T. |last28=Benz |first28=W. |last29=Bonfils |first29=X. |last30=Brandeker |first30=A. |journal=Astronomy & Astrophysics |volume=666 |pages=A118 |bibcode=2022A&A...666A.118J |s2cid=251442580 |display-authors=1 }}</ref> Surprisingly, spectra taken in 2021 have unambiguously indicated a presence of metal oxides and hydrides in the planetary atmosphere,<ref>{{citation|arxiv=2101.00469|title=The Hubble WFC3 Emission Spectrum of the Extremely Hot Jupiter KELT-9b|year=2021|last1=Changeat|first1=Quentin|last2=Edwards|first2=Billy|journal=The Astrophysical Journal Letters|volume=907|issue=1|pages=L22|doi=10.3847/2041-8213/abd84f|bibcode=2021ApJ...907L..22C|s2cid=230435556 |doi-access=free }}</ref> although higher resolution spectra taken in 2021 have not found any molecular emissions from the planetary dayside.<ref>{{citation|arxiv=2108.08389|year=2021|title=Confirmation of Iron Emission Lines and Nondetection of TiO on the Dayside of KELT-9b with MAROON-X|doi=10.3847/2041-8213/ac30e1|last1=Kasper|first1=David|last2=Bean|first2=Jacob L.|last3=Line|first3=Michael R.|last4=Seifahrt|first4=Andreas|last5=Stürmer|first5=Julian|last6=Pino|first6=Lorenzo|last7=Désert|first7=Jean-Michel|last8=Brogi|first8=Matteo|journal=The Astrophysical Journal Letters|volume=921|issue=1|pages=L18|bibcode=2021ApJ...921L..18K|s2cid=239024467 |doi-access=free }}</ref>


The [[thermosphere]] layer of KELT-9b is expected to heat up to {{convert|10000|-|11000|K|C F|0|abbr=on}}, driven by ionization of heavy metals atoms like iron.<ref>{{citation|arxiv=2010.00997|title=A data-driven approach to constraining the atmospheric temperature structure of the ultra-hot Jupiter KELT-9b|year=2020|doi=10.1051/0004-6361/202039061|last1=Fossati|first1=L.|last2=Shulyak|first2=D.|last3=Sreejith|first3=A. G.|last4=Koskinen|first4=T.|last5=Young|first5=M. E.|last6=Cubillos|first6=P. E.|last7=Lara|first7=L. M.|last8=France|first8=K.|last9=Rengel|first9=M.|last10=Cauley|first10=P. W.|last11=Turner|first11=J. D.|last12=Wyttenbach|first12=A.|last13=Yan|first13=F.|journal=Astronomy & Astrophysics|volume=643|pages=A131|bibcode=2020A&A...643A.131F|s2cid=225127226}}</ref>
The [[thermosphere]] layer of KELT-9b is expected to heat up to {{convert|10000|-|11000|K|C F|0|abbr=on}}, driven by ionization of heavy metals atoms like iron.<ref>{{citation|arxiv=2010.00997|title=A data-driven approach to constraining the atmospheric temperature structure of the ultra-hot Jupiter KELT-9b|year=2020|doi=10.1051/0004-6361/202039061|last1=Fossati|first1=L.|last2=Shulyak|first2=D.|last3=Sreejith|first3=A. G.|last4=Koskinen|first4=T.|last5=Young|first5=M. E.|last6=Cubillos|first6=P. E.|last7=Lara|first7=L. M.|last8=France|first8=K.|last9=Rengel|first9=M.|last10=Cauley|first10=P. W.|last11=Turner|first11=J. D.|last12=Wyttenbach|first12=A.|last13=Yan|first13=F.|journal=Astronomy & Astrophysics|volume=643|pages=A131|bibcode=2020A&A...643A.131F|s2cid=225127226}}</ref>
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== See also ==
== See also ==
*[[51 Pegasi b]], the first-discovered Hot Jupiter
*[[Gliese 3470 b]]
*[[List of hottest exoplanets]]
*[[List of hottest exoplanets]]

==References==
==References==
{{reflist|refs=
{{reflist|refs=
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{{wikinews|Astronomers reveal discovery of the hottest gas giant exoplanet known yet}}
{{wikinews|Astronomers reveal discovery of the hottest gas giant exoplanet known yet}}
*{{SIMBAD link|id=HD+195689|label=HD 195689}} SIMBAD entry for HD 195689
*{{SIMBAD link|id=HD+195689|label=HD 195689}} SIMBAD entry for HD 195689
{{Extrasolar-planet-stub}}
{{2016 in space}}
{{2016 in space}}
{{Stars of Cygnus}}
{{Stars of Cygnus}}

Latest revision as of 14:44, 18 November 2024

KELT-9b
Artist's impression of KELT-9b and its parent star
Orbital characteristics
0.03462+0.00110
−0.00093 AU
1.4811235±0.0000011[1] d
Inclination86.79±0.25[1]
StarHD 195689
Physical characteristics
1.891+0.061
−0.053[1] RJ
Mass2.17±0.56[2] MJ
Mean density
0.53000 ± 0.00015 g/cm3[citation needed]
Albedo<0.14[3]
Temperature4050±180[1] K

KELT-9b is an exoplanet and ultra-hot Jupiter that orbits the late B-type/early A-type star KELT-9,[4] located about 670 light-years from Earth.[4] Detected using the Kilodegree Extremely Little Telescope, the discovery of KELT-9b was announced in 2016.[5][1] As of June 2017, it is the hottest known exoplanet.[6]

Host star

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The host star, KELT-9, is 2 to 3 times larger and 2 to 3 times more massive than the sun. The surface temperature is 10,170 K (9,897 °C; 17,846 °F), unusually hot for a star with a transiting planet. Prior to the discovery of KELT-9b, only six A-type stars were known to have planets, of which the warmest, WASP-33, is significantly cooler at 7,430 K (7,157 °C; 12,914 °F); no B-type stars were previously known to host planets. KELT-9, classified as B9.5-A0[1][7] could be the first B-type star known to have a planet. KELT-9b occupies a circular but strongly inclined orbit a mere 0.03462 AU from KELT-9 with an orbital period of less than 1.5 days.[8][9]

Physical properties

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Exoplanet KELT-9b orbits host star KELT-9

KELT-9b is a relatively large giant planet at about 2.8 times the mass of Jupiter; however given that its radius is nearly twice that of Jupiter, its density is less than half that of it. Like many hot Jupiters, KELT-9b is tidally locked with its host star.[9] The outer boundary of its atmosphere nearly reaches its Roche lobe, implying that the planet is experiencing rapid atmospheric escape[10] driven by the extreme amount of radiation it receives from its host star.[9][8] In 2020, atmospheric loss rate was measured to be equal to 18 - 68 Earth masses per billion years.[11]

The planet's elemental abundances remain largely unknown as of 2022, but a low carbon-to-oxygen ratio is strongly suspected.[12]

This graph shows the average temperature and mass relative to Jupiter (Mj) of known exoplanets as of 2022

As of 2022, KELT-9b is the hottest known exoplanet, with dayside temperatures approaching 4,600 K (4,327 °C; 7,820 °F) — warmer than some K-type stars.[1][4] Molecules on the day side are broken into their component atoms, so that normally sequestered refractory elements can exist as atomic species, including neutral oxygen,[13] neutral and singly ionized atomic iron[14] (Fe and Fe+) and singly ionized titanium (Ti+),[15] only to temporarily reform once they reach the cooler night side,[4] which is indirectly confirmed by measured enhanced heat transfer efficiency of 0.3 between dayside and nightside, likely diven by the latent heat of dissociation and recombination of the molecular hydrogen.[3] Surprisingly, spectra taken in 2021 have unambiguously indicated a presence of metal oxides and hydrides in the planetary atmosphere,[16] although higher resolution spectra taken in 2021 have not found any molecular emissions from the planetary dayside.[17]

The thermosphere layer of KELT-9b is expected to heat up to 10,000–11,000 K (9,727–10,727 °C; 17,540–19,340 °F), driven by ionization of heavy metals atoms like iron.[18]

Size comparison
Jupiter KELT-9b
Jupiter Exoplanet

See also

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References

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  1. ^ a b c d e f g Gaudi, B. Scott; et al. (5 June 2017). "A giant planet undergoing extreme-ultraviolet irradiation by its hot massive-star host" (pdf). Nature. 546 (7659): 514–518. arXiv:1706.06723. Bibcode:2017Natur.546..514G. doi:10.1038/nature22392. ISSN 1476-4687. PMID 28582774. S2CID 205256410. Retrieved 2017-06-06.
  2. ^ Asnodkar, Anusha Pai; et al. (4 January 2022). "KELT-9 as an Eclipsing Double-lined Spectroscopic Binary: A Unique and Self-consistent Solution to the System". The Astronomical Journal. 163 (2). 40. arXiv:2110.15275. Bibcode:2022AJ....163...40P. doi:10.3847/1538-3881/ac32c7.
  3. ^ a b Jones, K.; et al. (2022), "The stable climate of KELT-9b", Astronomy & Astrophysics, 666: A118, arXiv:2208.04818, Bibcode:2022A&A...666A.118J, doi:10.1051/0004-6361/202243823, S2CID 251442580
  4. ^ a b c d Brennan, Pat; Cofield, Calia (24 January 2020). "For Hottest Planet, a Major Meltdown, Study Shows". NASA. Retrieved 24 January 2020.
  5. ^ Collins, Karen A.; Stassun, Keivan; Gaudi, B. Scott; Beatty, Thomas G.; Zhou, George; Latham, David W.; Bieryla, Allyson; Eastman, Jason D.; Siverd, Robert; Crepp, Justin R.; Pepper, Joshua (2016). "KELT-9b: A Case Study in Dynamical Planet Ingestion by a Hot Host Star". American Astronomical Society. 47: 204.03. Bibcode:2016DDA....4720403C.
  6. ^ Tribur, Melissa (2017-06-05). "Meet KELT-9b, the Hottest Exoplanet Ever Discovered". Eos. Retrieved 2022-10-28.
  7. ^ Jensen, K. S. (1981). "Spectral Classification in the MK System of 167 Northern HD Stars". Astronomy and Astrophysics Supplement. 45: 455. Bibcode:1981A&AS...45..455J.
  8. ^ a b KELT-9 b Exoplanet Exploration Program 2017
  9. ^ a b c NASA JPL, Pasadena CA (5 June 2017) Astronomers Find Planet Hotter Than Most Stars
  10. ^ Yan, Fei; Henning, Thomas (2 July 2018). "An extended hydrogen envelope of the extremely hot giant exoplanet KELT-9b". Nature Astronomy. 2 (9): 714–718. arXiv:1807.00869. Bibcode:2018NatAs...2..714Y. doi:10.1038/s41550-018-0503-3. ISSN 2397-3366. S2CID 119405172. Retrieved 18 August 2018.
  11. ^ Wyttenbach, A.; Mollière, P.; Ehrenreich, D.; Cegla, H. M.; Bourrier, V.; Lovis, C.; Pino, L.; Allart, R.; Seidel, J. V.; Hoeijmakers, H. J.; Nielsen, L. D.; Lavie, B.; Pepe, F.; Bonfils, X.; Snellen, I. A. G. (2020). "Mass loss rate and local thermodynamic state of KELT-9 b thermosphere from the hydrogen Balmer series". Astronomy & Astrophysics. 638: A87. arXiv:2004.13733. Bibcode:2020A&A...638A..87W. doi:10.1051/0004-6361/201937316. S2CID 216641961.
  12. ^ Jacobs, Bob; Désert, Jean-Michel; Pino, Lorenzo; Line, Michael R.; Bean, Jacob L.; Khorshid, Niloofar; Schlawin, Everett; Arcangeli, Jacob; Barat, Saugata; Jens Hoeijmakers, H.; Komacek, Thaddeus D.; Mansfield, Megan; Parmentier, Vivien; Thorngren, Daniel (2022), "A strong H− opacity signal in the near-infrared emission spectrum of the ultra-hot Jupiter KELT-9b", Astronomy & Astrophysics, 668: L1, arXiv:2211.10297, Bibcode:2022A&A...668L...1J, doi:10.1051/0004-6361/202244533, S2CID 253708097
  13. ^ Borsa, Francesco; Fossati, Luca; Koskinen, Tommi; Young, Mitchell E.; Shulyak, Denis (2022), "High-resolution detection of neutral oxygen and non-LTE effects in the atmosphere of KELT-9b", Nature Astronomy, 6 (2): 226–231, arXiv:2112.12059, doi:10.1038/s41550-021-01544-4, S2CID 245385802
  14. ^ Pino, L.; Désert, J. M.; Brogi, M.; Malavolta, L.; Wyttenbach, A.; Line, M.; Hoeijmakers, J.; Fossati, L.; Bonomo, A. S.; Nascimbeni, V.; Panwar, V.; Affer, L.; Benatti, S.; Biazzo, K.; Bignamini, A.; Borsa, F.; Carleo, I.; Claudi, R.; Cosentino, R.; Covino, E.; Damasso, M.; Desidera, S.; Giacobbe, P.; Harutyunyan, A.; Lanza, A. F.; Leto, G.; Maggio, A.; Maldonado, J.; Mancini, L.; et al. (2020). "Neutral Iron Emission Lines from the Day-side of KELT-9b -- the GAPS Programme with HARPS-N at TNG XX". The Astrophysical Journal. 894 (2): L27. arXiv:2004.11335. Bibcode:2020ApJ...894L..27P. doi:10.3847/2041-8213/ab8c44. S2CID 216080480.
  15. ^ Hoeijmakers, H. Jens; Ehrenreich, David; Heng, Kevin; Kitzmann, Daniel; Grimm, Simon L.; Allart, Romain; Deitrick, Russell; Wyttenbach, Aurélien; Oreshenko, Maria; Pino, Lorenzo; Rimmer, Paul B.; Molinari, Emilio; Di Fabrizio, Luca (15 August 2018). "Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b". Nature. 560 (7719): 453–455. arXiv:1808.05653. Bibcode:2018Natur.560..453H. doi:10.1038/s41586-018-0401-y. ISSN 1476-4687. PMC 6322651. PMID 30111838.
  16. ^ Changeat, Quentin; Edwards, Billy (2021), "The Hubble WFC3 Emission Spectrum of the Extremely Hot Jupiter KELT-9b", The Astrophysical Journal Letters, 907 (1): L22, arXiv:2101.00469, Bibcode:2021ApJ...907L..22C, doi:10.3847/2041-8213/abd84f, S2CID 230435556
  17. ^ Kasper, David; Bean, Jacob L.; Line, Michael R.; Seifahrt, Andreas; Stürmer, Julian; Pino, Lorenzo; Désert, Jean-Michel; Brogi, Matteo (2021), "Confirmation of Iron Emission Lines and Nondetection of TiO on the Dayside of KELT-9b with MAROON-X", The Astrophysical Journal Letters, 921 (1): L18, arXiv:2108.08389, Bibcode:2021ApJ...921L..18K, doi:10.3847/2041-8213/ac30e1, S2CID 239024467
  18. ^ Fossati, L.; Shulyak, D.; Sreejith, A. G.; Koskinen, T.; Young, M. E.; Cubillos, P. E.; Lara, L. M.; France, K.; Rengel, M.; Cauley, P. W.; Turner, J. D.; Wyttenbach, A.; Yan, F. (2020), "A data-driven approach to constraining the atmospheric temperature structure of the ultra-hot Jupiter KELT-9b", Astronomy & Astrophysics, 643: A131, arXiv:2010.00997, Bibcode:2020A&A...643A.131F, doi:10.1051/0004-6361/202039061, S2CID 225127226
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