TRAPPIST-1g

TRAPPIST-1g, also designated as 2MASS J23062928-

0502285 g and K2-112 g, is an exoplanet orbiting around TRAPPIST-1g
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.

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]
Artist's impression of TRAPPIST-1g.
(February 2018)
Physical characteristics Discovery[1]
Discovered by Michaël Gillon et al.
Mass, radius, and temperature Discovery site Spitzer Space Telescope
Discovery date 22 February 2017
TRAPPIST-1g has a radius of 1.129 R🜨 and a mass of
Detection Transit
1.321 M🜨, with a density only slightly less than Earth's,[2] method
though initial estimates suggested its density was only
Orbital characteristics[2]
4.186 g/cm3 , about 76% of Earth's.[3] Based on mass-
radius calculations and its distant location relative to its host Semi-major 0.046 83 ± 0.000 40 AU
star (0.047 AU) and the fact that the planet only receives axis
25.2% of the stellar flux that Earth does, the planet is likely Eccentricity 0.002 08 ± 0.000 58[3]
covered by a thick ice envelope if an atmosphere does not
Orbital period 12.352 446 ± 0.000 054 d
exist. (sidereal)
Inclination 89.742° ± 0.012°
Atmosphere Argument of 191.34° ± 13.83°[3]
periastron
TRAPPIST-1g could have a global water ocean or an
Star TRAPPIST-1[4]
exceptionally thick steam atmosphere.[3] According to a
simulation of magma ocean-atmosphere interaction, Physical characteristics[2]
TRAPPIST-1g is likely to retain a large fraction of Mean radius +0.015
1.129 −0.013 R🜨
primordial steam atmosphere during the initial stages of
evolution, and therefore today is likely to possess a thick Mass 1.321 ± 0.038 M🜨
ocean covered by atmosphere containing hundreds of bars Mean density +0.136
5.042 −0.158 g/cm3
of abiotic oxygen.[8]
Surface 1.035 ± 0.026 g
gravity 10.15 ± 0.25 m/s2
On 31 August 2017, astronomers at the Hubble Space Temperature Teq: 197.3 ± 1.9 K
Telescope reported the first evidence of possible water (−75.8 °C; −104.5 °F)[5]
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
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" (http://www.eso.org/p
ublic/archives/releases/sciencepapers/eso1706/eso1706a.pdf) (PDF). Nature. 542 (7642):
456–460. arXiv:1703.01424 (https://arxiv.org/abs/1703.01424).
Bibcode:2017Natur.542..456G (https://ui.adsabs.harvard.edu/abs/2017Natur.542..456G).
doi:10.1038/nature21360 (https://doi.org/10.1038%2Fnature21360). PMC 5330437 (https://w
 ww.ncbi.nlm.nih.gov/pmc/articles/PMC5330437). PMID 28230125 (https://pubmed.ncbi.nlm.
nih.gov/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 (https://arxiv.org/abs/2010.01074). Bibcode:2021PSJ.....2....1A (https://ui.a
dsabs.harvard.edu/abs/2021PSJ.....2....1A). doi:10.3847/psj/abd022 (https://doi.org/10.384
7%2Fpsj%2Fabd022). S2CID 222125312 (https://api.semanticscholar.org/CorpusID:222125
312).
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 (https://arxiv.org/abs/1802.01377).
Bibcode:2018A&A...613A..68G (https://ui.adsabs.harvard.edu/abs/2018A&A...613A..68G).
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S2CID 3441829 (https://api.semanticscholar.org/CorpusID: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 (https://arxiv.org/abs/1712.01911). Bibcode:2018ApJ...853...30V (h
ttps://ui.adsabs.harvard.edu/abs/2018ApJ...853...30V). doi:10.3847/1538-4357/aaa023 (http
s://doi.org/10.3847%2F1538-4357%2Faaa023). S2CID 54034373 (https://api.semanticschol
ar.org/CorpusID: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 (https://arxiv.org/abs/2006.13826).
Bibcode:2020A&A...640A.112D (https://ui.adsabs.harvard.edu/abs/2020A&A...640A.112D).
doi:10.1051/0004-6361/201937392 (https://doi.org/10.1051%2F0004-6361%2F201937392).
ISSN 0004-6361 (https://www.worldcat.org/issn/0004-6361). S2CID 220041987 (https://api.s
emanticscholar.org/CorpusID:220041987).
6. "Temperate Earth-Sized Planets Found in Extraordinarily Rich Planetary System
TRAPPIST-1" (http://spaceref.com/astronomy/temperate-earth-sized-planets-found-in-extrao
rdinarily-rich-planetary-system-trappist-1.html). SpaceRef. 22 February 2017. Retrieved
11 February 2017.
7. "NASA telescope reveals largest batch of Earth-size, habitable-zone planets around single
star" (https://exoplanets.nasa.gov/news/1419/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 (https://arxiv.org/abs/2008.09599),
Bibcode:2021AsBio..21.1325B (https://ui.adsabs.harvard.edu/abs/2021AsBio..21.1325B),
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9. Bourrier, Vincent; de Wit, Julien; Jäger, Mathias (31 August 2017). "Hubble delivers first hints
of possible water content of TRAPPIST-1 planets" (http://www.spacetelescope.org/news/hei
c1713/). 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" (http://indianexpress.com/article/t
echnology/science/first-evidence-of-water-found-on-trappist-1-planets-4827977/). The Indian
Express. Retrieved 4 September 2017.
11. Wang, Wu, Barclay, Laughlin (2017). "Updated Masses for the TRAPPIST-1 Planets".
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tro-ph.EP)].
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 (https://arxiv.org/abs/17
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S2CID 119464994 (https://api.semanticscholar.org/CorpusID:119464994).

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