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Gliese 436 b

Coordinates:Sky map11h42m11.0941s,+26° 42′ 23.652″
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Gliese 436 b / Awohali
Size comparison of Awohali with Neptune
Discovery[1]
Discovered byButler,Vogt,
Marcyet al.
Discovery siteCalifornia, USA
Discovery dateAugust 31, 2004
Radial velocity, Transit
Designations
Awohali[2]
Orbital characteristics
0.028±0.01AU
Eccentricity0.152+0.009
−0.008[3]
2.643904±0.000005[4]d
Inclination85.8+0.21
−0.25[4]
2451552.077[3]
325.8+5.5
−5.7[3]
Semi-amplitude17.38±0.17[3]
StarNoquisi
Physical characteristics
4.327 ± 0.183[5][6]R🜨
Mass21.36+0.20
−0.21[3]ME
1.51g/cm3(0.055lb/cu in)
1.18g
Temperature712 K (439 °C; 822 °F)[5]

Gliese 436 b/ˈɡliːzə/(sometimes calledGJ 436 b,[7]formally namedAwohali[2]) is aNeptune-sizedexoplanetorbiting thered dwarfGliese 436.[1]It was the firsthot Neptunediscovered with certainty (in 2007) and was among the smallest-knowntransiting planetsin mass and radius, until the much smallerKeplerexoplanet discoveries begancirca2010.

In December 2013, NASA reported thatcloudsmay have been detected in theatmosphereof GJ 436 b.[8][9][10][11]

Nomenclature

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In August 2022, this planet and its host star were included among 20 systems to be named by the thirdNameExoWorldsproject.[12]The approved names, proposed by a team from theUnited States,were announced in June 2023. Gliese 436 b is namedAwohaliand its host star is namedNoquisi,after theCherokeewords for "eagle" and "star".[2]

Discovery

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Awohali was discovered in August 2004 byR. Paul ButlerandGeoffrey Marcyof theCarnegie Institute of WashingtonandUniversity of California, Berkeley,respectively, using theradial velocity method.Together with55 Cancri e,it was the first of a new class of planets with a minimum mass (M sini) similar to Neptune.[1]

The planet was recorded totransitits star by an automatic process atNMSUon January 11, 2005, but this event went unheeded at the time.[13]In 2007, Michael Gillon fromGeneva UniversityinSwitzerlandled a team that observed the transit, grazing the stellar disc relative to Earth. Transit observations led to the determination of its exact mass and radius, both of which are very similar to that of Neptune, making Awohali at that time the smallest known transiting extrasolar planet. The planet is about four thousand kilometers larger in diameter than Uranus and five thousand kilometers larger than Neptune and slightly more massive. Awohali orbits at a distance of four million kilometers or one-fifteenth the average distance ofMercuryfrom theSun.[14]

Physical characteristics

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Possible interior structure of Gliese 436 b
Formation of aheliumatmosphereon ahelium planet,possibly like Gliese 436 b.

The planet's surface temperature is estimated from measurements taken as it passes behind the star to be 712 K (439 °C; 822 °F).[5]This temperature is significantly higher than would be expected if the planet were only heated by radiation from its star, which was prior to this measurement, estimated at 520 K. Whatever energy tidal effects deliver to the planet, it does not affect its temperature significantly.[15]Agreenhouse effectwould result in a much greater temperature than the predicted 520–620 K.[14]

Its main constituent was initially predicted to be hot "ice"in various exotic high-pressure forms,[14][16]which would remain solid despite the high temperatures, because of the planet's gravity.[17]The planet could have formed further from its current position, as a gas giant, and migrated inwards with the other gas giants. As it approached its present position, radiation from the star would have blown off the planet's hydrogen layer viacoronal mass ejection.[18]

However, when the radius became better known, ice alone was not enough to account for the observed size. An outer layer ofhydrogenandhelium,accounting for up to ten percent of the mass, was needed on top of the ice to account for the observed planetary radius.[5][4]This obviates the need for an ice core. Alternatively, the planet may consist of a dense rocky core surrounded by a lesser amount of hydrogen.[19]

Observations of the planet'sbrightness temperaturewith theSpitzer Space Telescopesuggest a possible thermochemical disequilibrium in the atmosphere of this exoplanet. Results published in Nature suggest that Awohali’s dayside atmosphere is abundant in CO and deficient in methane (CH4) by a factor of ~7,000. This result is unexpected because, based on current models at its temperature, atmospheric carbon should prefer CH4over CO.[20][21][22][23]In part for this reason, it has also been hypothesized to be a possiblehelium planet.[24]

In June 2015, scientists reported that the atmosphere of Awohali was evaporating,[25]resulting in a giant cloud around the planet and, due to radiation from the host star, a long trailing tail 14×10^6km (9×10^6mi) long.[26]

Artist impression of Gliese 436b shows the enormous comet-like cloud of hydrogen boiling off.[27]

Orbital characteristics

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One orbit around the star takes only about twodays,15.5hours.Awohali orbit is likely misaligned with its star's rotation.[22]The eccentricity of Awohali’s orbit is inconsistent with models of planetary system evolution. To have maintained its eccentricity over time requires that it be accompanied by another planet.[5][28]

A study published inNaturefound that the orbit of Awohali is nearly perpendicular (inclined by 103.2+12.8
−11.5degrees)[29]to the stellar equator of Noquisi and suggests that the eccentricity and misalignment of the orbit could have resulted from interactions with a yet undetected companion. The inward migration caused by this interaction could have triggered the atmospheric escape that sustains its giant exosphere.[30]

See also

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References

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  1. ^abcButler, R. Paul; et al. (2004)."A Neptune-Mass Planet Orbiting the Nearby M Dwarf GJ 436".The Astrophysical Journal.617(1): 580–588.arXiv:astro-ph/0408587.Bibcode:2004ApJ...617..580B.doi:10.1086/425173.S2CID118893640.
  2. ^abc"2022 Approved Names".nameexoworlds.iau.org.IAU.Archivedfrom the original on 1 May 2024.Retrieved7 June2023.
  3. ^abcdeTrifonov, Trifon; Kürster, Martin; Zechmeister, Mathias; Tal-Or, Lev; Caballero, José A.; Quirrenbach, Andreas; Amado, Pedro J.; Ribas, Ignasi; Reiners, Ansgar; et al. (2018). "The CARMENES search for exoplanets around M dwarfs. First visual-channel radial-velocity measurements and orbital parameter updates of seven M-dwarf planetary systems".Astronomy and Astrophysics.609.A117.arXiv:1710.01595.Bibcode:2018A&A...609A.117T.doi:10.1051/0004-6361/201731442.S2CID119340839.
  4. ^abcBean, J.L.; et al. (2008)."A Hubble Space Telescope transit light curve for GJ 436b".Astronomy & Astrophysics.486(3): 1039–1046.arXiv:0806.0851.Bibcode:2008A&A...486.1039B.doi:10.1051/0004-6361:200810013.S2CID6351375.Archivedfrom the original on 2010-04-08.Retrieved2008-08-07.
  5. ^abcdeDrake Deming; Joseph Harrington; Gregory Laughlin; Sara Seager; Navarro, Sarah B.; Bowman, William C.; Karen Horning (2007). "Spitzer Transit and Secondary Eclipse Photometry of GJ 436b".The Astrophysical Journal.667(2): L199–L202.arXiv:0707.2778.Bibcode:2007ApJ...667L.199D.doi:10.1086/522496.S2CID13349666.
  6. ^Confirmed,Pont, F.; Gilliland, R. L.; Knutson, H.; Holman, M.; Charbonneau, D. (2008). "Transit infrared spectroscopy of the hot neptune around GJ 436 with the Hubble Space Telescope".Monthly Notices of the Royal Astronomical Society: Letters.393(1): L6–L10.arXiv:0810.5731.Bibcode:2009MNRAS.393L...6P.doi:10.1111/j.1745-3933.2008.00582.x.S2CID3746845.
  7. ^Beust, Hervé; et al. (August 1, 2012). "Dynamical evolution of the Gliese 436 planetary system - Kozai migration as a potential source for Gliese 436b's eccentricity".Astronomy.545:A88.arXiv:1208.0237.Bibcode:2012A&A...545A..88B.doi:10.1051/0004-6361/201219183.S2CID10253533.
  8. ^Harrington, J.D.; Weaver, Donna; Villard, Ray (December 31, 2013)."Release 13-383 - NASA's Hubble Sees Cloudy Super-Worlds With Chance for More Clouds".NASA.Archivedfrom the original on January 2, 2014.RetrievedJanuary 1,2014.
  9. ^Moses, Julianne (January 1, 2014). "Extrasolar planets: Cloudy with a chance of dustballs".Nature.505(7481): 31–32.Bibcode:2014Natur.505...31M.doi:10.1038/505031a.PMID24380949.S2CID4408861.
  10. ^Knutson, Heather; et al. (January 1, 2014). "A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b".Nature.505(7481): 66–68.arXiv:1401.3350.Bibcode:2014Natur.505...66K.doi:10.1038/nature12887.PMID24380953.S2CID4454617.
  11. ^Kreidberg, Laura; et al. (January 1, 2014). "Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b".Nature.505(7481): 69–72.arXiv:1401.0022.Bibcode:2014Natur.505...69K.doi:10.1038/nature12888.hdl:1721.1/118780.PMID24380954.S2CID4447642.
  12. ^"List of ExoWorlds 2022".nameexoworlds.iau.org.IAU.8 August 2022.Archivedfrom the original on 8 March 2023.Retrieved27 August2022.
  13. ^Coughlin, Jeffrey L.; Stringfellow, Guy S.; Becker, Andrew C.; Mercedes Lopez-Morales; Fabio Mezzalira; Tom Krajci (2008). "New observations and a possible detection of parameter variations in the transits of Gliese 436b".The Astrophysical Journal.689(2): L149–L152.arXiv:0809.1664.Bibcode:2008ApJ...689L.149C.doi:10.1086/595822.S2CID14893633.
  14. ^abcM. Gillon; et al. (2007)."Detection of transits of the nearby hot Neptune GJ 436 b"(PDF).Astronomy and Astrophysics.472(2): L13–L16.arXiv:0705.2219.Bibcode:2007A&A...472L..13G.doi:10.1051/0004-6361:20077799.S2CID13552824.Archived(PDF)from the original on 2020-10-21.Retrieved2008-08-08.
  15. ^Brian Jackson; Richard Greenberg; Rory Barnes (2008). "Tidal Heating of Extra-Solar Planets".The Astrophysical Journal.681(2): 1631–1638.arXiv:0803.0026.Bibcode:2008ApJ...681.1631J.doi:10.1086/587641.S2CID42315630.
  16. ^Shiga, David (6 May 2007)."Strange alien world made of" hot ice "".New Scientist. Archived fromthe originalon July 6, 2008.Retrieved2007-05-16.
  17. ^Fox, Maggie (May 16, 2007)."Hot" ice "may cover recently discovered planet".Science News.Scientific American.com.Archivedfrom the original on 2012-09-07.Retrieved2008-08-06.
  18. ^H. Lammer; et al. (2007)."The impact of nonthermal loss processes on planet masses from Neptunes to Jupiters"(PDF).Geophysical Research Abstracts.9(7850).Archived(PDF)from the original on 2019-12-15.Retrieved2008-08-18.By analogy withGliese 876 d.
  19. ^E. R. Adams; S. Seager; L. Elkins-Tanton (February 2008). "Ocean Planet or Thick Atmosphere: On the Mass-Radius Relationship for Solid Exoplanets with Massive Atmospheres".The Astrophysical Journal.673(2): 1160–1164.arXiv:0710.4941.Bibcode:2008ApJ...673.1160A.doi:10.1086/524925.S2CID6676647.
  20. ^Stevenson, KB; Harrington, J; Nymeyer, S; et al. (22 April 2010). "Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b".Nature.464(7292): 1161–1164.arXiv:1010.4591.Bibcode:2010Natur.464.1161S.doi:10.1038/nature09013.PMID20414304.S2CID4416249.
  21. ^GJ436b - Where's the methane?Archived2010-05-14 at theWayback MachinePlanetary Sciences Group at the University of Central Florida, Orlando
  22. ^abKnutson, Heather A. (2011). "ASpitzerTransmission Spectrum for the Exoplanet GJ 436b ".Astrophysical Journal.735, 27 (1): 27.arXiv:1104.2901.Bibcode:2011ApJ...735...27K.doi:10.1088/0004-637X/735/1/27.S2CID18669291.
  23. ^LINE, Michael R.; VASISHT, Gautam; CHEN, Pin; ANGERHAUSEN, D.; YANG, Yuk L. (2011). "Thermochemical and Photochemical Kinetics in Cooler Hydrogen Dominated Extrasolar Planets".Astrophysical Journal.738, 32 (1): 32.arXiv:1104.3183.Bibcode:2011ApJ...738...32L.doi:10.1088/0004-637X/738/1/32.S2CID15087062.,abstract in the arXiv titled "Thermochemistry and Photochemistry in Cooler Hydrogen Dominated Extrasolar Planets: The Case of GJ436b"
  24. ^"Helium-Shrouded Planets May Be Common in Our Galaxy".SpaceDaily. 16 June 2015.Archivedfrom the original on 11 August 2019.Retrieved3 August2015.
  25. ^D. Ehrenreich; V. Bourrier; P. Wheatley; A. Lecavelier des Etangs; G. Hébrard; S. Udry; X. Bonfils; X. Delfosse; J.-M. Désert; D. K. Sing; A. Vidal-Madjar (25 June 2015). "A Giant Comet-like Cloud of Hydrogen Escaping from the warm Neptune-mass Exoplanet GJ 436b".Nature.522(7557): 459–461.arXiv:1506.07541.Bibcode:2015Natur.522..459E.doi:10.1038/nature14501.PMID26108854.S2CID4388969.
  26. ^Bhanoo, Sindya N. (25 June 2015)."A Planet with a Tail Nine Million Miles Long".New York Times.Archivedfrom the original on 25 June 2015.Retrieved25 June2015.
  27. ^"Hubble sees atmosphere being stripped from Neptune-sized exoplanet".Retrieved25 June2015.
  28. ^Bean, Jacob L.; Andreas Seifahrt (2008). "Observational Consequences of the Recently Proposed Super-Earth Orbiting GJ436".Astronomy & Astrophysics.487(2): L25–L28.arXiv:0806.3270.Bibcode:2008A&A...487L..25B.doi:10.1051/0004-6361:200810278.S2CID14811323.
  29. ^Bourrier, V.; Zapatero Osorio, M. R.; Allart, R.; Attia, O.; Cretignier, M.; Dumusque, X.; Lovis, C.; Adibekyan, V.; Borsa, F.; Figueira, P.; Hernández, J. I. González; Mehner, A.; Santos, N. C.; Schmidt, T.; Seidel, J. V.; Sozzetti, A.; Alibert, Y.; Casasayas-Barris, N.; Ehrenreich, D.; Lo Curto, G.; Martins, C. J. A. P.; Di Marcantonio, P.; Mégevand, D.; Nunes, N. J.; Palle, E.; Poretti, E.; Sousa, S. G. (2022), "The polar orbit of the warm Neptune GJ 436b seen with VLT/ESPRESSO",Astronomy & Astrophysics,663:A160,arXiv:2203.06109,Bibcode:2022A&A...663A.160B,doi:10.1051/0004-6361/202142559,S2CID247139822
  30. ^Bourrier, Vincent; et al. (2018). "Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star".Nature.553(7689): 477–480.arXiv:1712.06638.Bibcode:2018Natur.553..477B.doi:10.1038/nature24677.PMID29258300.S2CID4468186.{{cite journal}}:CS1 maint: multiple names: authors list (link)

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