TRAPPIST-1h

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

0502285 h, is an exoplanet orbiting around the ultra-cool TRAPPIST-1h
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.

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 Artist's impression of TRAPPIST-1h.

Discovery[1]
Discovered by Michaël Gillon et al.
Mass, radius, and temperature
Discovery site Spitzer Space Telescope
TRAPPIST-1h has a radius of 0.755 R🜨, a mass of Discovery date 22 February 2017
0.326 M🜨, and about 57% Earth's surface gravity.[2] It was Detection Transit
initially estimated to have a density of 3.97 g/cm3, similar method
to that of Mars. Given this density, about ≤5% of its mass Orbital characteristics[2]
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 Semi-major 0.061 89 ± 0.000 53 AU
axis
does. It has an equilibrium temperature of 169 K (−104 °C;
−155 °F), similar to that of Earth's south pole. Eccentricity 0.005 67 ± 0.001 21[3]
Orbital period 18.772 866 ± 0.000 214 d
(sidereal)
Host star
Inclination 89.805° ± 0.013°
TRAPPIST-1h orbits the ultracool dwarf star TRAPPIST- Argument of 338.92° ± 9.66°[3]
1. It is 0.121 R☉ and 0.089 M☉ , with a temperature of periastron
2511 K and an age between 3 and 8 billion years. For Star TRAPPIST-1[4]
comparison, the Sun has a temperature of 5778 K and is
Physical characteristics[2]
about 4.5 billion years old. TRAPPIST-1 is also very dim,
with about 0.0005 times the luminosity of the Sun. The Mean radius 0.755 ± 0.014 R🜨
star's apparent magnitude, or how bright it appears from Mass 0.326 ± 0.020 M🜨
Earth's perspective, is 18.8. Therefore, it is too dim to be +0.322
Mean density 4.147 −0.302 g/cm3
seen with the naked eye.
Surface 0.570 ± 0.038 g
gravity 5.58 ± 0.37 m/s2
Orbit
Temperature Teq: 171.7 ± 1.7 K
Despite it being the most distant known planet in its system, (−101.5 °C; −150.6 °F)[5]
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
List of transiting exoplanets

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
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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).
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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).
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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. 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" (https://iopscience.iop.org/article/10.108
8/1538-3873/ab9504/meta). Publications of the Astronomical Society of the Pacific. 132
(1014): 084402. Bibcode:2020PASP..132h4402Q (https://ui.adsabs.harvard.edu/abs/2020P
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2Fab9504). S2CID 219964895 (https://api.semanticscholar.org/CorpusID: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 (https://arxiv.org/abs/1703.04166).
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of possible water content of TRAPPIST-1 planets" (http://www.spacetelescope.org/news/hei
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(2022), "Near-infrared transmission spectrum of TRAPPIST-1 h usingHubbleWFC3 G141
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13. Garcia, L. J.; Moran, S. E.; Rackham, B. V.; Wakeford, H. R.; Gillon, M.; De Wit, J.; Lewis, N.
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