TRAPPIST-1h

TRAPPIST-1h, also designated as 2MASS J23062928-0502285 h, is an exoplanet orbiting around the ultra-cool dwarf star TRAPPIST-1, located 40.7 light-years (12.5 parsecs) away from Earth in the constellation Aquarius. It was one of four new exoplanets to be discovered orbiting the star in 2017 using observations from the Spitzer Space Telescope.[6][7] In the following years, more studies were able to refine its physical parameters.

TRAPPIST-1h
Artist's impression of TRAPPIST-1h.
Discovery[1]
Discovered byMichaël Gillon et al.
Discovery siteSpitzer Space Telescope
Discovery date22 February 2017
Transit
Orbital characteristics[2]
0.06189±0.00053 AU
Eccentricity0.00567±0.00121[3]
18.772866±0.000214 d
Inclination89.805°±0.013°
338.92°±9.66°[3]
StarTRAPPIST-1[4]
Physical characteristics[2]
Mean radius
0.755±0.014 R🜨
Mass0.326±0.020 M🜨
Mean density
4.147+0.322
−0.302 g/cm3
0.570±0.038 g
5.58±0.37 m/s2
TemperatureTeq: 171.7±1.7 K (−101.5 °C; −150.6 °F)[5]

    The outermost known planet in its system, it is roughly one third the mass of Earth, and about 76% as large. Its relatively low density indicates that it is likely water-rich, like several other planets in the system.[8]

    Physical characteristics

    Mass, radius, and temperature

    TRAPPIST-1h has a radius of 0.755 R🜨, a mass of 0.326 M🜨, and about 57% Earth's surface gravity.[2] It was initially estimated to have a density of 3.97 g/cm3, similar to that of Mars. Given this density, about ≤5% of its mass may be water, likely in the form of a thick ice shell,[8] since it only receives about 13% of the stellar flux that Earth does. It has an equilibrium temperature of 169 K (−104 °C; −155 °F), similar to that of Earth's south pole.

    Host star

    TRAPPIST-1h orbits the ultracool dwarf star TRAPPIST-1. It is 0.121 R☉ and 0.089 M☉, with a temperature of 2511 K and an age between 3 and 8 billion years. For comparison, the Sun has a temperature of 5778 K and is about 4.5 billion years old. TRAPPIST-1 is also very dim, with about 0.0005 times the luminosity of the Sun. The star's apparent magnitude, or how bright it appears from Earth's perspective, is 18.8. Therefore, it is too dim to be seen with the naked eye.

    Orbit

    Despite it being the most distant known planet in its system, TRAPPIST-1h orbits its host star with an orbital period of 18.868 days and an orbital radius of about 0.0619 AU. This is even smaller than Mercury's orbit around the Sun (which is about 0.38 AU).[9]

    Stable liquid water

    Although TRAPPIST-1h's orbit falls near its star's frost line, it could harbor liquid water[10][11] under an H2-rich atmosphere, either primordial or resulting from continuous outgassing combined with internal heating,[9] although existence of such atmosphere was strongly disfavored by observations in 2021[12] and 2022.[13] It could also potentially harbor a subsurface ocean by way of tidal heating, which could lead to cryovolcanism in the form of erupting geysers.[8]

    See also

    References
    1. Gillon, M.; Triaud, A. H. M. J.; Demory, B.-O.; Jehin, E.; Agol, E.; Deck, K. M.; Lederer, S. M.; De Wit, J.; Burdanov, A.; Ingalls, J. G.; Bolmont, E.; Leconte, J.; Raymond, S. N.; Selsis, F.; Turbet, M.; Barkaoui, K.; Burgasser, A.; Burleigh, M. R.; Carey, S. J.; Chaushev, A.; Copperwheat, C. M.; Delrez, L.; Fernandes, C. S.; Holdsworth, D. L.; Kotze, E. J.; Van Grootel, V.; Almleaky, Y.; Benkhaldoun, Z.; Magain, P.; Queloz, D. (2017). "Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1" (PDF). Nature. 542 (7642): 456–460. arXiv:1703.01424. Bibcode:2017Natur.542..456G. doi:10.1038/nature21360. PMC 5330437. PMID 28230125.
    2. Agol, Eric; Dorn, Caroline; Grimm, Simon L.; Turbet, Martin; et al. (1 February 2021). "Refining the Transit-timing and Photometric Analysis of TRAPPIST-1: Masses, Radii, Densities, Dynamics, and Ephemerides". The Planetary Science Journal. 2 (1): 1. arXiv:2010.01074. Bibcode:2021PSJ.....2....1A. doi:10.3847/psj/abd022. S2CID 222125312.
    3. Grimm, Simon L.; Demory, Brice-Olivier; Gillon, Michael; Dorn, Caroline; Agol, Eric; Burdanov, Artem; Delrez, Laetitia; Sestovic, Marko; Triaud, Amaury H.M.J.; Turbet, Martin; Bolmont, Emeline; Caldas, Anthony; de Wit, Julien; Jehin, Emmanuel; Leconte, Jeremy; Raymond, Sean N.; Van Grootel, Valerie; Burgasser, Adam J.; Carey, Sean; Fabrycky, Daniel; Heng, Kevin; Hernandez, David M.; Ingalls, James G.; Lederer, Susan; Selsis, Franck; Queloz, Didier (2018). "The nature of the TRAPPIST-1 exoplanets". Astronomy & Astrophysics. 613: A68. arXiv:1802.01377. Bibcode:2018A&A...613A..68G. doi:10.1051/0004-6361/201732233. S2CID 3441829.
    4. Van Grootel, Valerie; Fernandes, Catarina S.; Gillon, Michaël; Jehin, Emmanuel; Scuflaire, Richard; et al. (2018). "Stellar parameters for TRAPPIST-1". The Astrophysical Journal. 853 (1): 30. arXiv:1712.01911. Bibcode:2018ApJ...853...30V. doi:10.3847/1538-4357/aaa023. S2CID 54034373.
    5. Ducrot, E.; Gillon, M.; Delrez, L.; Agol, E.; et al. (1 August 2020). "TRAPPIST-1: Global results of the Spitzer Exploration Science Program Red Worlds". Astronomy & Astrophysics. 640: A112. arXiv:2006.13826. Bibcode:2020A&A...640A.112D. doi:10.1051/0004-6361/201937392. ISSN 0004-6361. S2CID 220041987.
    6. "Temperate Earth-Sized Planets Found in Extraordinarily Rich Planetary System TRAPPIST-1". SpaceRef. 22 February 2017. Retrieved 11 February 2017.
    7. "NASA telescope reveals largest batch of Earth-size, habitable-zone planets around single star". Exoplanet Exploration: Planets Beyond our Solar System (Press release). Retrieved 22 February 2017.
    8. Quick, Lynnae C.; Roberge, Aki; Barr Mlinar, Amy; Hedman, Matthew M. (18 June 2020). "Forecasting Rates of Volcanic Activity on Terrestrial Exoplanets and Implications for Cryovolcanic Activity on Extrasolar Ocean Worlds". Publications of the Astronomical Society of the Pacific. 132 (1014): 084402. Bibcode:2020PASP..132h4402Q. doi:10.1088/1538-3873/ab9504. S2CID 219964895.
    9. Luger, Rodrigo; Sestovic, Marko; Kruse, Ethan; Grimm, Simon L.; Demory, Brice-Olivier; et al. (2017). "A terrestrial-sized exoplanet at the snow line of TRAPPIST-1". Nature Astronomy. 1: 0129. arXiv:1703.04166. Bibcode:2017NatAs...1E.129L. doi:10.1038/s41550-017-0129. S2CID 54770728.
    10. Bourrier, Vincent; de Wit, Julien; Jäger, Mathias (31 August 2017). "Hubble delivers first hints of possible water content of TRAPPIST-1 planets". www.SpaceTelescope.org. Retrieved 4 September 2017.
    11. PTI (4 September 2017). "First evidence of water found on TRAPPIST-1 planets - The results suggest that the outer planets of the system might still harbour substantial amounts of water. This includes the three planets within the habitable zone of the star, lending further weight to the possibility that they may indeed be habitable". The Indian Express. Retrieved 4 September 2017.
    12. Gressier, A.; Mori, M.; Changeat, Q.; Edwards, B.; Beaulieu, J. P.; Marcq, E.; Charnay, B. (2022), "Near-infrared transmission spectrum of TRAPPIST-1 h usingHubbleWFC3 G141 observations", Astronomy & Astrophysics, 658: A133, arXiv:2112.05510, Bibcode:2022A&A...658A.133G, doi:10.1051/0004-6361/202142140, S2CID 245091619
    13. Garcia, L. J.; Moran, S. E.; Rackham, B. V.; Wakeford, H. R.; Gillon, M.; De Wit, J.; Lewis, N. K. (2022), "HST/WFC3 transmission spectroscopy of the cold rocky planet TRAPPIST-1h", Astronomy & Astrophysics, 665: A19, arXiv:2203.13698, Bibcode:2022A&A...665A..19G, doi:10.1051/0004-6361/202142603, S2CID 247748871
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