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Gliese 436 b

Coordinates: Sky map 11h 42m 11.0941s, +26° 42′ 23.652″
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Gliese 436 b / Awohali
Size comparison of Awohali with Neptune
Discovery[1]
Discovered byButler, Vogt,
Marcy et al.
Discovery siteCalifornia, USA
Discovery dateAugust 31, 2004
Radial velocity, Transit
Designations
Awohali[2]
Orbital characteristics
0.028±0.01 AU
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
Mean density
1.51 g/cm3 (0.055 lb/cu in)
1.18 g
Temperature712 K (439 °C; 822 °F)[5]

Gliese 436 b /ˈɡliːzə/ (sometimes called GJ 436 b,[7] formally named Awohali[2]) is a Neptune-sized exoplanet orbiting the red dwarf Gliese 436.[1] It was the first hot Neptune discovered with certainty (in 2007) and was among the smallest-known transiting planets in mass and radius, until the much smaller Kepler exoplanet discoveries began circa 2010.

In December 2013, NASA reported that clouds may have been detected in the atmosphere of GJ 436 b.[8][9][10][11]

Nomenclature

[edit]

In August 2022, this planet and its host star were included among 20 systems to be named by the third NameExoWorlds project.[12] The approved names, proposed by a team from the United States, were announced in June 2023. Gliese 436 b is named Awohali and its host star is named Noquisi, after the Cherokee words for "eagle" and "star".[2]

Discovery

[edit]

Awohali was discovered in August 2004 by R. Paul Butler and Geoffrey Marcy of the Carnegie Institute of Washington and University of California, Berkeley, respectively, using the radial velocity method. Together with 55 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 to transit its star by an automatic process at NMSU on January 11, 2005, but this event went unheeded at the time.[13] In 2007, Michael Gillon from Geneva University in Switzerland led 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 of Mercury from the Sun.[14]

Physical characteristics

[edit]
Possible interior structure of Awohali
Formation of a helium atmosphere on a helium planet, possibly like Awohali.

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] A greenhouse effect would 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 via coronal mass ejection.[18]

However, when the radius became better known, ice alone was not enough to account for the observed size. An outer layer of hydrogen and helium, 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's brightness temperature with the Spitzer Space Telescope suggest 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 CH4 over CO.[20][21][22][23] In part for this reason, it has also been hypothesized to be a possible helium 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 14×10^6 km (9×10^6 mi) long.[26]

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

Orbital characteristics

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One orbit around the star Noquisi takes only about two days, 15.5 hours. Awohali orbit is likely misaligned with Noquisi’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 in Nature found that the orbit of Awohali is nearly perpendicular (inclined by 103.2+12.8
−11.5 degrees)[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. ^ a b c Butler, 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. S2CID 118893640.
  2. ^ a b c "2022 Approved Names". nameexoworlds.iau.org. IAU. Archived from the original on 1 May 2024. Retrieved 7 June 2023.
  3. ^ a b c d e Trifonov, 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. S2CID 119340839.
  4. ^ a b c Bean, 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. S2CID 6351375. Archived from the original on 2010-04-08. Retrieved 2008-08-07.
  5. ^ a b c d e Drake 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. S2CID 13349666.
  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. S2CID 3746845.
  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. S2CID 10253533.
  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. Archived from the original on January 2, 2014. Retrieved January 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. PMID 24380949. S2CID 4408861.
  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. PMID 24380953. S2CID 4454617.
  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. PMID 24380954. S2CID 4447642.
  12. ^ "List of ExoWorlds 2022". nameexoworlds.iau.org. IAU. 8 August 2022. Archived from the original on 8 March 2023. Retrieved 27 August 2022.
  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. S2CID 14893633.
  14. ^ a b c M. 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. S2CID 13552824. Archived (PDF) from the original on 2020-10-21. Retrieved 2008-08-08.
  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. S2CID 42315630.
  16. ^ Shiga, David (6 May 2007). "Strange alien world made of "hot ice"". New Scientist. Archived from the original on July 6, 2008. Retrieved 2007-05-16.
  17. ^ Fox, Maggie (May 16, 2007). "Hot "ice" may cover recently discovered planet". Science News. Scientific American.com. Archived from the original on 2012-09-07. Retrieved 2008-08-06.
  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. Retrieved 2008-08-18. By analogy with Gliese 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. S2CID 6676647.
  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. PMID 20414304. S2CID 4416249.
  21. ^ GJ436b - Where's the methane? Archived 2010-05-14 at the Wayback Machine Planetary Sciences Group at the University of Central Florida, Orlando
  22. ^ a b Knutson, Heather A. (2011). "A Spitzer Transmission 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. S2CID 18669291.
  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. S2CID 15087062., 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. Archived from the original on 11 August 2019. Retrieved 3 August 2015.
  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. PMID 26108854. S2CID 4388969.
  26. ^ Bhanoo, Sindya N. (25 June 2015). "A Planet with a Tail Nine Million Miles Long". New York Times. Archived from the original on 25 June 2015. Retrieved 25 June 2015.
  27. ^ "Hubble sees atmosphere being stripped from Neptune-sized exoplanet". Retrieved 25 June 2015.
  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. S2CID 14811323.
  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, S2CID 247139822
  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. PMID 29258300. S2CID 4468186.{{cite journal}}: CS1 maint: multiple names: authors list (link)

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