View source for Epsilon Indi Ab

{{Short description|Gas giant orbiting Epsilon Indi A}}
{{Infobox planet
| extrasolarplanet   = yes
| name               = Epsilon Indi Ab
| image              = Epsilon Indi Ab (MIRI Image).png
| caption            = Epsilon Indi Ab imaged by [[James Webb Space Telescope|JWST]] [[Mid-Infrared Instrument|MIRI]]. The star motif marks the position of its host star; whose light is blocked by a [[coronagraph]].
| apsis              = astron
| discovery_ref      = <ref name="Feng2018"/>
| discoverer         = Fabo Feng, et al.
| discovery_site     = 
| discovered         = 21 March 2018 (suspected since 2002)
| discovery_method   = [[Doppler spectroscopy|Radial velocity]]
| alt_names          = <!--(Any alternative names for the body)-->
| orbit_ref          = <ref name=Feng2024/>
| epoch              = 
| periastron         = 
| apoastron          = 
| semimajor          = {{val|29.2|3.3|3.4|ul=AU}}
| avg_speed          = <!--(Average orbital speed)-->
| eccentricity       = {{val|0.399|0.059|0.076}}
| period             = {{val|180|32|31}} years
| inclination        = {{val|105.4|2.5|2.4|u=deg}}
| asc_node           = 
| angular_dist       = 
| arg_peri           = 
| time_periastron    = 
| semi-amplitude     = 
| mean_anomaly       = 
| star               = [[Epsilon Indi]] A
| physical_ref       = <ref name="Matthews2024"/>
| mean_radius        = 1.08 [[Jupiter radius|<var>R</var><sub>Jup</sub>]]{{efn|name=rad}}
| surface_area       = 
| volume             = 
| density            = 
| mass               = {{val|7.29|0.60|0.61|ul=Jupiter mass}}<ref name=Feng2024/>
| surface_grav       = <!--Equatorial surface gravity-->
| moment_of_inertia_factor = 
| escape_velocity    = 
| albedo             = 
| single_temperature = {{convert|275|K|C F|lk=on}}
}}

'''Epsilon Indi Ab''' is a [[gas giant]] [[exoplanet]] orbiting the star [[Epsilon Indi]] A, about 11.9 [[light-year]]s away in the [[constellation]] of [[Indus (constellation)|Indus]]. The planet was confirmed to exist in 2018.<ref name="Feng2018"/> It orbits at around 30 [[Astronomical unit|AU]] (almost as far as [[Neptune]] from the Sun) with a period of around 180 years and a relatively high [[orbital eccentricity|eccentricity]] of 0.4, and has a mass around seven times that of [[Jupiter]].<ref name=Feng2024/> It was [[direct imaging|directly imaged]] using the [[James Webb Space Telescope]] in 2023<ref name="JWSTProposal2243"/> and the image was released in 24 july, 2024.<ref name="JWSTImages2024-07-24" />

{{As of|2024}}, Epsilon Indi Ab is the nearest exoplanet to be directly imaged, and with a temperature of about {{convert|275|K|C F|lk=on}}, is also the coolest exoplanet to be directly imaged, and cooler than all but one imaged [[brown dwarf]] (the exception being the planetary-mass [[WISE 0855−0714]]).<ref name="JWSTImages2024-07-24" /> It is predicted, based on evolutionary models, to have a [[luminosity]] around to {{val|6.31|e=-8|ul=solar luminosity}}.<ref name="Matthews2024"/>

The Epsilon Indi system also contains a pair of brown dwarfs, Epsilon Indi Ba and Bb, at a wide separation from the primary star. As such, this system provides a benchmark case for the study of the formation of gas giants and brown dwarfs.<ref name="Feng2018"/>

== History of observations ==
The first evidence of Epsilon Indi Ab was found in 2002 when measurements of the [[radial velocity]] of Epsilon Indi by Endl et al. appeared to show a trend that indicated a planetary companion with an orbital period of more than 20 years. A substellar object with a [[minimum mass]] of {{Jupiter mass|1.6|link=y}} and orbital separation of roughly 6.5 AU was within the parameters of the highly approximate data.<ref name="ESO2002" />

A visual search using the [[European Southern Observatory|ESO]]'s [[Very Large Telescope]] found one potential candidate. However, a subsequent examination by the [[Hubble Space Telescope]] [[Near Infrared Camera and Multi-Object Spectrometer|NICMOS]] showed that this was a background object.<ref name="Geissler2007"/> As of 2009, a search for an unseen companion at 4 μm failed to detect an orbiting object. These observations further constrained the hypothetical object to be 5–20 times the mass of Jupiter, orbiting between 10 and 20 AU and have an inclination of more than 20°. Alternatively, it may be an exotic stellar remnant.<ref name="Janson2009"/>

A longer study of radial velocity, using the [[High Accuracy Radial Velocity Planet Searcher|HARPS]] echelle spectrometer, to follow up on Endl's findings, was published in a paper by M. Zechmeister et al. in 2013. The findings confirm that, quoting the paper, "ε Ind A has a steady long-term trend still explained by a planetary companion".<ref name="Zechmeister2013" /> This refined the radial-velocity trend observed and indicated a planetary companion with an orbital period greater than 30 years and a minimum mass of {{Jupiter mass|0.97|link=y}}. The radial-velocity trend was observed through all the observations taken using the HARPS spectrometer, but due to the long period predicted for just one orbit of the object around ε Indi A, more than 30 years, the phase coverage was not yet complete.<ref name="Zechmeister2013" />

In March 2018, a [[preprint]] was posted to [[arXiv]] that confirmed the existence of Epsilon Indi Ab using [[Doppler spectroscopy|radial velocity]] measurements.<ref name="Feng2018"/> In December 2019, the confirmation of this planet, along with updated parameters from both radial velocity and [[astrometry]], was published by Fabo Feng et al. in ''[[Monthly Notices of the Royal Astronomical Society]]''. This study found a semi-major axis of about 11.6 AU, an orbital period of about 45 years, an eccentricity of about 0.26, and a mass of {{Jupiter mass|3.25}}.<ref name="Feng2019"/> Updated orbital solutions were published in 2023, finding a higher eccentricity.<ref name="Philipot2023"/><ref name="Feng2023"/>

A direct imaging attempt of this planet using the [[James Webb Space Telescope]] was performed in 2023,<ref name="JWSTProposal2243"/> and the image was released in 2024. The detected planet's mass and orbit are different from what was predicted based on radial velocity and astrometry observations.<ref name="JWSTImages2024-07-24" /> The JWST and [[Very Large Telescope|VLT]]/VISIR observations imply a [[super-Jupiter]] with a mass of about 6 Jupiter masses. The object is fainter than expected in the shorter wavelengths, which might be due to absorption by [[methane]], [[carbon dioxide]], and [[carbon monoxide]] commonly found in giant planets. This might be confirmed in the future with a spectrum. Alternatively this could be explained with a cloudy atmosphere.<ref>{{Cite web |title=Webb images nearest super-Jupiter, opening a new window to exoplanet research |url=https://www.mpia.de/news/science/2024-12-eps-ind-matthews |access-date=2024-07-24 |website=www.mpia.de |language=en}}</ref> A second direct imaging attempt on this system to confirm the nature of this planet has been approved.<ref name="JWSTProposal5037"/> The new orbital parameters were calculated with archived radial velocity data, the Hipparcos-Gaia astrometry of the host star and the position of the planet from the images. The planet has a semi-major axis of around 30 AU, an eccentricity of 0.4 and an inclination of 104°. The planet-star separation is 4.1 [[Minute and second of arc|arcsec]] in JWST MIRI data and 4.8 arcsec in VLT VISIR data. It is undetected in VLT NaCo observations.<ref name="Matthews2024"/> The temperature of 275 K is slightly warmer or similar to the nearby Y-dwarf [[WISE 0855−0714|WISE J0855−0714]] (225 to 260 K or 285 K), making Epsilon Indi Ab likely one of the coldest objects to be directly imaged outside the [[Solar System|solar system]]. At this temperature, which is warmer than [[Jupiter]] (T<sub>eff</sub>=125 K),<ref name="Coulter22"/> but colder than 350 K, it is predicted that such an exoplanet could have [[Snow|water ice]] clouds and lower layers of [[sulfide]] clouds.<ref name="Morley2014"/>

== See also ==
* [[Epsilon Eridani b]], another nearby Jupiter-like exoplanet
* [[Gliese 832 b]], another nearby Jupiter-like exoplanet
* [[List of directly imaged exoplanets]]
* [[TZ Arietis#Planetary system|TZ Arietis b]]

==Notes==
{{Notelist|notes=

{{Efn|name=rad|1=Calculated, using the [[Stefan-Boltzmann law]] and the planet's [[effective temperature]] and luminosity, with respect to the [[Sun|solar]] nominal effective temperature of 5,772&nbsp;[[Kelvin|K]]:<math display="block">\sqrt{\biggl(\frac{5,772}{275}\biggr)^4 \cdot 10^{-7.2}} = 0.1106\ R_\odot.</math>}}


}}

== References ==
{{reflist|refs=

<ref name="Morley2014">{{Cite journal |last1=Morley |first1=Caroline V. |last2=Marley |first2=Mark S. |last3=Fortney |first3=Jonathan J. |last4=Lupu |first4=Roxana |last5=Saumon |first5=Didier |last6=Greene |first6=Tom |last7=Lodders |first7=Katharina |date=2014-05-01 |title=Water Clouds in Y Dwarfs and Exoplanets |url=https://iopscience.iop.org/article/10.1088/0004-637X/787/1/78 |journal=The Astrophysical Journal |volume=787 |issue=1 |pages=78 |arxiv=1404.0005 |bibcode=2014ApJ...787...78M |doi=10.1088/0004-637X/787/1/78 |issn=0004-637X}}</ref>

<ref name="Coulter22">{{Cite journal |last1=Coulter |first1=Daniel J. |last2=Barnes |first2=Jason W. |last3=Fortney |first3=Jonathan J. |date=2022-11-01 |title=Jupiter and Saturn as Spectral Analogs for Extrasolar Gas Giants and Brown Dwarfs |journal=The Astrophysical Journal Supplement Series |volume=263 |issue=1 |pages=15 |arxiv=2208.05541 |bibcode=2022ApJS..263...15C |doi=10.3847/1538-4365/ac886a |issn=0067-0049 |doi-access=free}}</ref>

<ref name="ESO2002">{{cite journal | author=Endl, M. | author2=Kürster, M. | author3=Els, S. | author4=Hatzes, A. P. | author5=Cochran, W. D. | author6=Dennerl, K. | author7=Döbereiner, S. | title=The planet search program at the ESO Coudé Echelle spectrometer. III. The complete Long Camera survey results | journal=[[Astronomy & Astrophysics]] | volume=392 | issue=2 | pages=671–690 | date=2002 | bibcode=2002A&A...392..671E | doi=10.1051/0004-6361:20020937 | arxiv=astro-ph/0207512| s2cid=17393347 }}</ref>

<ref name="Geissler2007">{{cite journal | last=Geißler | first=K. | author2=Kellner, S. | author3=Brandner, W. | author4=Masciadri, E. | author5=Hartung, M. | author6=Henning, T. | author7=Lenzen, R. | author8=Close, L. | author9=Endl, M. | author10=Kürster, M. | title=A direct and differential imaging search for sub-stellar companions to epsilon Indi A | journal=Astronomy and Astrophysics | date=2007 | volume=461 | issue=2 | pages=665–668 | bibcode=2007A&A...461..665G | doi=10.1051/0004-6361:20065843 | arxiv=astro-ph/0611336| s2cid=119442720 }}</ref>

<ref name="Janson2009">{{cite journal | author=Janson, M. | display-authors=etal | title=Imaging search for the unseen companion to ε Ind A – improving the detection limits with 4 μm observations | journal=Monthly Notices of the Royal Astronomical Society | volume=399 | issue=1 | pages=377–384 | date=August 10, 2009 | doi=10.1111/j.1365-2966.2009.15285.x | doi-access=free | bibcode=2009MNRAS.399..377J | arxiv=0906.4145| s2cid=16314685 }}</ref>

<ref name=Feng2024>{{Citation |last=Feng |first=Fabo |title=Lessons learned from the detection of wide companions by radial velocity and astrometry |date=2024-12-19 |arxiv=2412.14542 |last2=Xiao |first2=Guang-Yao |last3=Jones |first3=Hugh R. A. |last4=Jenkins |first4=James S. |last5=Pena |first5=Pablo |last6=Sun |first6=Qinghui}}</ref>

<ref name="Zechmeister2013">{{cite journal | title=The planet search programme at the ESO CES and HARPS. IV. The search for Jupiter analogues around solar-like stars <!--Reducible--> | last1=Zechmeister | first1=M. | last2=Kürster | first2=M | last3=Endl | first3=M. | last4=Lo Curto | first4=G. | last5=Hartman | first5=H. | last6=Nilsson | first6=H. | last7=Henning | first7=T. | last8=Hatzes | first8=A. | last9=Cochran | first9=W. D. | journal=[[Astronomy & Astrophysics]] | date=April 2013 | volume=552 | pages=62 | doi=10.1051/0004-6361/201116551 | bibcode=2013A&A...552A..78Z | arxiv=1211.7263 | s2cid=53694238 }}</ref>

<ref name="Feng2018">{{cite arXiv| title=Detection of the closest Jovian exoplanet in the Epsilon Indi triple system| eprint=1803.08163| first1=Fabo| last1=Feng| first2=Mikko| last2=Tuomi| first3=Hugh R. A.| last3=Jones| date=23 March 2018|class = astro-ph.EP}}</ref>

<ref name="Feng2019">{{Citation | title=Detection of the nearest Jupiter analog in radial velocity and astrometry data | first1=Fabo | last1=Feng | first2=Guillem | last2=Anglada-Escudé | first3=Mikko | last3=Tuomi | first4=Hugh R. A. | last4=Jones | first5=Julio | last5=Chanamé | first6=Paul R. | last6=Butler | first7=Markus | last7=Janson | journal=[[Monthly Notices of the Royal Astronomical Society]] | arxiv=1910.06804 | date=14 October 2019 | volume=490 | issue=4 | pages=5002–5016 | doi=10.1093/mnras/stz2912 | doi-access=free | bibcode=2019MNRAS.490.5002F | s2cid=204575783 }}</ref>

<ref name="Philipot2023">{{cite journal |last1=Philipot |first1=F. |last2=Lagrange |first2=A.-M. |display-authors=etal |arxiv=2301.01263 |title=Updated characterization of long-period single companion by combining radial velocity, relative astrometry, and absolute astrometry |journal=Astronomy & Astrophysics |date=January 2023|volume=670 |pages=A65 |doi=10.1051/0004-6361/202245396 |bibcode=2023A&A...670A..65P |s2cid=255393653 }}</ref>

<ref name="Feng2023">{{cite journal |last1=Feng |first1=Fabo |last2=Butler |first2=R. Paul |display-authors=etal |date=July 2023 |title=Revised orbits of the two nearest Jupiters |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume= 525|issue= 1|pages= 607–619|doi=10.1093/mnras/stad2297 |doi-access=free |arxiv=2307.13622 |bibcode=2023MNRAS.525..607F}}</ref>

<ref name="JWSTProposal2243">
{{cite web
 |url=https://www.stsci.edu/jwst/science-execution/program-information.html?id=2243
 |title=A direct detection of the closest Jupiter analog with JWST/MIRI
 |website=stsci.edu
 |publisher=[[Space Telescope Science Institute|STScI]]
 |access-date=31 July 2022
 |quote=We will collect the first direct images of a radial velocity planet, by targeting Eps Indi Ab with JWST/MIRI. [...] Our simulations confirm that we will detect Eps Indi Ab's thermal emission at high confidence, regardless of its cloud properties or thermal evolution.
}}</ref>

<ref name="JWSTProposal5037">
{{cite web
 |url=https://www.stsci.edu/jwst/science-execution/program-information?id=5037
 |title=Confirmation of the closest directly detected exoplanet: a super-Jupiter orbiting Eps Ind A
 |website=stsci.edu
 |publisher=[[Space Telescope Science Institute|STScI]]
 |access-date=1 March 2024
 |quote=JWST Cycle 1 images of Eps Ind A reveal a candidate companion that is consistent in color and magnitude with a massive (~10Mjup) planet. However, the position angle and mass of the candidate is different than expected from RV/astrometric models of the companion orbit - perhaps suggesting there are two giant planets in this system, with only one of these detected in the MIRI images.
}}</ref>

<ref name="JWSTImages2024-07-24">
{{cite web
 |url=https://science.nasa.gov/missions/webb/nasas-webb-images-cold-exoplanet-12-light-years-away/
 |title=NASA's Webb Images Cold Exoplanet 12 Light-Years Away
 |website=nasa.gov
 |publisher=NASA Webb Mission Team
 |access-date=Jul 24, 2024
 |quote=
}}</ref>

<ref name="Matthews2024">
{{cite journal
 |last1=Matthews |first1=E. C.
 |last2=Carter |first2=A. L.
 |display-authors=etal
 |title=A temperate super-Jupiter imaged with JWST in the mid-infrared
 |url=https://www.nature.com/articles/s41586-024-07837-8.epdf?sharing_token=rDmIHPiLMl77NbVHtDcNGdRgN0jAjWel9jnR3ZoTv0Nc2mduqijOgU08KVCfXgyTyeY9f3uMYgxWiSdta81Y3w7HMv4naw7o4Gl0w_iF06iej7hWIJFS__ui3TPqa5Z6IpEk7UMnCUdEGQOjTJF60h8HPpxUutnFPv_UqIZlqvDNTK273QCp7aD7CkdFuR4o8IyHo_b7w-GjzJWK6IUu8g9xmtkAdOr2SLA0f8vFWrmOXYKbXaW-9XlUm_VT_AhC6E9pf_LQnU96WMsUGGfeNA%3D%3D&tracking_referrer=www.cbc.ca
 |journal=[[Nature (journal)|Nature]]
 |volume= |issue= |pages=
 |date=July 2024
 |doi=10.1038/s41586-024-07837-8
|pmid=39048015
 |doi-access=free
 |pmc=11424479
 }}</ref>

}}

{{Nearest systems|2}}
{{Indus (constellation)}}

[[Category:Exoplanets discovered in 2018]]
[[Category:Exoplanets detected by radial velocity]]
[[Category:Exoplanets detected by astrometry]]
[[Category:Exoplanets detected by direct imaging]]
[[Category:Giant planets]]
[[Category:Indus (constellation)]]