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TRAPPIST-1g

Artist's impression of TRAPPIST-1g. (February 2018)
Discovery
Discovered by	Michaël Gillon et al.
Discovery site	Spitzer Space Telescope
Discovery date	22 February 2017
Detection method	Transit
Orbital characteristics
Semi-major axis	0.04683±0.00040 AU
Eccentricity	0.00208±0.00058
Orbital period (sidereal)	12.352446±0.000054 d
Inclination	89.742°±0.012°
Argument of periastron	191.34°±13.83°
Star	TRAPPIST-1
Physical characteristics
Mean radius	1.129+0.015 −0.013 R🜨
Mass	1.321±0.038 M🜨
Mean density	5.042+0.136 −0.158 g/cm
Surface gravity	1.035±0.026 g 10.15±0.25 m/s
Temperature	Teq: 197.3±1.9 K (−75.8 °C; −104.5 °F)

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. The exoplanet is within the optimistic habitable zone of its host star. 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.

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.

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, though initial estimates suggested its density was only 4.186 g/cm, about 76% of Earth's. 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. 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.

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

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 2,550 K. The age of the star is about 7.6±2.2 billion years old. In comparison, the Sun is 4.6 billion years old and has a temperature of 5,778 K. The star is metal-rich, with a metallicity () 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, 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

• List of extrasolar candidates for liquid water
• List of transiting exoplanets
• List of potentially habitable exoplanets
• List of nearest terrestrial exoplanet candidates
• TRAPPIST-1d
• TRAPPIST-1e

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). 21 February 2017. Retrieved 22 February 2017.
8. Quick, Lynnae C.; Roberge, Aki; Tovar Mendoza, Guadalupe; Quintana, Elisa V.; and Youngblood, Allison A. (4 October 2023). "Prospects for Cryovolcanic Activity on Cold Ocean Planets". The Astrophysical Journal. 956 (29): 29. Bibcode:2023ApJ...956...29Q. doi:10.3847/1538-4357/ace9b6.
9. 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
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. Wang, Wu, Barclay, Laughlin (2017). "Updated Masses for the TRAPPIST-1 Planets". arXiv:1704.04290 .{{cite arXiv}}: CS1 maint: multiple names: authors list (link)
13. Burgasser, Adam J. and 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.

v t e Exoplanets
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Habitability	Astrobiology Astrooceanography Circumstellar habitable zone Earth analog Extraterrestrial liquid water Galactic habitable zone Habitability of binary star systems Habitability of F-type main-sequence star systems Habitability of K-type main-sequence star systems Habitability of natural satellites Habitability of neutron star systems Habitability of red dwarf systems Habitability of yellow dwarf systems Habitable zone for complex life List of potentially habitable exoplanets Tholin Superhabitable planet
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Lists	Exoplanetary systems Host stars Multiplanetary systems Stars with proto-planetary discs Exoplanets Discoveries Extremes Firsts Nearest Largest Heaviest Terrestrial candidates Kepler 1–500 501–1000 1001–1500 1501–2000 K2 Potentially habitable Proper names Discovered exoplanets by year before 2000 2000–2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024
Other	Carl Sagan Institute Exoplanet naming convention Exoplanet phase curves Exoplanetary Circumstellar Environments and Disk Explorer Extragalactic planet Extrasolar planets in fiction Geodynamics of terrestrial exoplanets Neptunian desert Nexus for Exoplanet System Science Planets in globular clusters Small planet radius gap Sudarsky's gas giant classification
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v t e 2017 in space
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Outer space portal Category:2016 in outer space — Category:2017 in outer space — Category:2018 in outer space

v t e Constellation of Aquarius
Aquarius in Chinese astronomy Aquarius Stream List of stars in Aquarius
Stars	Bayer α (Sadalmelik) β (Sadalsuud) γ (Sadachbia) δ (Skat) ε (Albali) ζ η θ (Ancha) ι κ (Situla) λ (Hydor) μ ν ξ (Bunda) ο π ρ σ τ τ υ φ χ ψ (91) ψ ψ ω ω A A b b b c c c d e f g g h i i i k α PsA C Flamsteed 1 4 5 7 8 9 10 11 12 14 15 16 17 18 19 20 21 24 26 28 29 30 32 35 36 37 39 40 41 42 44 45 47 49 50 51 54 56 58 60 61 64 65 67 70 72 74 75 77 78 81 82 84 85 87 94 96 97 100 Variable R U AE DV EP EW EZ FO HK IL HU IZ LP HR 8017 8056 8121 8263 8363 8453 8500 8507 8581 8612 8629 8645 8716 8783 8836 8856 8879 8924 9014 HD 206610 (Bosona) 210277 212771 (Lionrock) 215152 219617 220466 220689 222093 222582 Other 2MASS J21392676+0220226 BD−22 5866 Gliese 849 K2-21 K2-28 K2-58 K2-72 K2-138 LS IV-14 116 Sneden's Star TRAPPIST-1 WASP-6 (Márohu) WASP-47 WASP-69 WASP-75
Exoplanets ψ Aquarii b Gliese 849 b Gliese 876 b c d e HD 206610 b HD 210277 b HD 212771 b (Victoriapeak) HD 221416 b HD 222582 b K2-66b K2-72b c d e K2-138b TRAPPIST-1b c d e f g h WASP-6b
Star clusters Messier 2 Messier 72 Messier 73
Nebulae Helix Nebula Saturn Nebula
Galaxies	NGC 6975 7001 7010 7047 7051 7065 7069 7077 7081 7184 7222 7252 7257 7301 7302 7393 7492 7585 7592 7600 7606 7723 7727 7759 Other Aquarius Dwarf ESO 603-G21 Lyman-alpha blob 1 PGC 1228197 PHL 293B SMM J2135-0102 WISE J224607.57−052635.0 J2345-0449
Galaxy clusters Abell 2597 RXC J2211.7-0350 XMMXCS 2215-1738
Astronomical events SN 2213-1745
Category

• Astronomy
• Biology
• Space

• Exoplanets discovered in 2017
• Near-Earth-sized exoplanets
• Near-Earth-sized exoplanets in the habitable zone
• Transiting exoplanets
• TRAPPIST-1
• Aquarius (constellation)
• 2MASS objects
• Ice exoplanets