TRAPPIST-1g

TRAPPIST-1g, also designated as 2MASS J23062928-0502285 g and K2-112 g, 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] The exoplanet is within the optimistic habitable zone of its host star.[7] It was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured.

TRAPPIST-1g
Artist's impression of TRAPPIST-1g. (February 2018)
Discovery[1]
Discovered byMichaël Gillon et al.
Discovery siteSpitzer Space Telescope
Discovery date22 February 2017
Transit
Orbital characteristics[2]
0.04683±0.00040 AU
Eccentricity0.00208±0.00058[3]
12.352446±0.000054 d
Inclination89.742°±0.012°
191.34°±13.83°[3]
StarTRAPPIST-1[4]
Physical characteristics[2]
Mean radius
1.129+0.015
−0.013 R🜨
Mass1.321±0.038 M🜨
Mean density
5.042+0.136
−0.158 g/cm3
1.035±0.026 g
10.15±0.25 m/s2
TemperatureTeq: 197.3±1.9 K (−75.8 °C; −104.5 °F)[5]

    The second most distant known planet in its system, TRAPPIST-1g is a planet somewhat larger than Earth and with a similar density, meaning it is likely a rocky planet.[2]

    Physical characteristics

    Mass, radius, and temperature

    TRAPPIST-1g has a radius of 1.129 R🜨 and a mass of 1.321 M🜨, with a density only slightly less than Earth's,[2] though initial estimates suggested its density was only 4.186 g/cm3, about 76% of Earth's.[3] Based on mass-radius calculations and its distant location relative to its host star (0.047 AU) and the fact that the planet only receives 25.2% of the stellar flux that Earth does, the planet is likely covered by a thick ice envelope if an atmosphere does not exist.

    Atmosphere

    TRAPPIST-1g could have a global water ocean or an exceptionally thick steam atmosphere.[3] According to a simulation of magma ocean-atmosphere interaction, TRAPPIST-1g is likely to retain a large fraction of primordial steam atmosphere during the initial stages of evolution, and therefore today is likely to possess a thick ocean covered by atmosphere containing hundreds of bars of abiotic oxygen.[8]

    On 31 August 2017, astronomers at the Hubble Space Telescope reported the first evidence of possible water content on the TRAPPIST-1 exoplanets.[9][10][11]

    Host star

    The planet orbits an (M-type) ultracool dwarf star named TRAPPIST-1. The star has a mass of 0.08 M☉ and a radius of 0.11 R☉. It has a temperature of 2550 K. The age of the star is about 7.6±2.2 billion years old.[12] In comparison, the Sun is 4.6 billion years old and has a temperature of 5778 K. The star is metal-rich, with a metallicity ([Fe/H]) of 0.04, or 109% the solar amount. This is particularly odd as such low-mass stars near the boundary between brown dwarfs and hydrogen-fusing stars should be expected to have considerably less metal content than the Sun. Its luminosity (L☉) is 0.05% of that of the Sun.

    The star's apparent magnitude, or how bright it appears from Earth's perspective, is 18.8, too dim to be seen with the naked eye.

    Orbit

    TRAPPIST-1g orbits its host star with an orbital period of about 12.354 days and an orbital radius of about 0.0451 times that of Earth's (compared to the distance of Mercury from the Sun, which is about 0.38 AU). This is in the outer limit of TRAPPIST-1's theoretical habitable zone. The orbit of TRAPPIST-1g has an eccentricity of 0.00208,[3] much lower than that of Earth and the lowest in its system. Its orbit varies by only about 41,000 kilometers (compared to about 5 million km for Earth), meaning the planet's climate is likely very stable. It is in a 3:2 orbital resonance with TRAPPIST-1h and a 3:4 resonance with TRAPPIST-1f.

    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. Barth, Patrick; Carone, Ludmila; Barnes, Rory; Noack, Lena; Mollière, Paul; Henning, Thomas (2021), "Magma Ocean Evolution of the TRAPPIST-1 Planets", Astrobiology, 21 (11): 1325–1349, arXiv:2008.09599, Bibcode:2021AsBio..21.1325B, doi:10.1089/ast.2020.2277, PMID 34314604, S2CID 221246323
    9. 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.
    10. 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.
    11. Wang, Wu, Barclay, Laughlin (2017). "Updated Masses for the TRAPPIST-1 Planets". arXiv:1704.04290 [astro-ph.EP].{{cite arXiv}}: CS1 maint: multiple names: authors list (link)
    12. Burgasser, Adam J.; Mamajek, Eric E. (17 August 2017). "On the Age of the TRAPPIST-1 System". The Astrophysical Journal. 845 (2): 110. arXiv:1706.02018. Bibcode:2017ApJ...845..110B. doi:10.3847/1538-4357/aa7fea. S2CID 119464994.
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