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TRAPPIST-1e

Artist's impression of TRAPPIST-1e from 2018, depicted here as a tidally locked planet with a liquid ocean. The actual appearance of the exoplanet is currently unknown, but based on its density, it is likely not entirely covered in water.
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	0.02925±0.00025 AU
Eccentricity	0.00510±0.00058
Orbital period (sidereal)	6.101013±0.000035 d
Inclination	89.793°±0.048°
Argument of periastron	108.37°±8.47°
Star	TRAPPIST-1
Physical characteristics
Mean radius	0.920+0.013 −0.012 R🜨
Mass	0.692±0.022 M🜨
Mean density	4.885+0.168 −0.182 g/cm
Surface gravity	0.817±0.024 g 8.01±0.24 m/s
Temperature	Teq: 249.7±2.4 K (−23.5 °C; −10.2 °F)

TRAPPIST-1e, also designated as 2MASS J23062928-0502285 e, is a rocky, close-to-Earth-sized exoplanet orbiting within the habitable zone around the ultracool dwarf star TRAPPIST-1, located 40.7 light-years (12.5 parsecs; 385 trillion kilometers; 239 trillion miles) away from Earth in the constellation of Aquarius. Astronomers used the transit method to find the exoplanet, a method that measures the dimming of a star when a planet crosses in front of it.

The exoplanet was one of seven discovered orbiting the star using observations from the Spitzer Space Telescope. Three of the seven (e, f, and g) are in the habitable zone/"goldilocks" zone. TRAPPIST-1e is similar to Earth's mass, radius, density, gravity, temperature, and stellar flux. It is also confirmed that TRAPPIST-1e lacks a cloud-free hydrogen-dominated atmosphere, meaning it is more likely to have a compact atmosphere like the terrestrial planets in the Solar System.

In November 2018, researchers determined that of the seven exoplanets in the multi-planetary system, TRAPPIST-1e has the best chance of being an Earth-like ocean planet, and the one most worthy of further study regarding habitability. According to the Habitable Exoplanets Catalog, TRAPPIST-1e is among the best potentially habitable exoplanets discovered.

Physical characteristics

Mass, radius, density, composition and temperature

TRAPPIST-1e was detected with the transit method, where the planet blocked a small percentage of its host star's light when passing between it and Earth. This allowed scientists to accurately determine the planet's radius at 0.920 R_🜨, with a small uncertainty of about 83 km (52 mi). Transit-timing variations and advanced computer simulations helped constrain the planet's mass, which turned out to be 0.692 M_🜨, or about 15% less massive than Venus. TRAPPIST-1e has 82% the surface gravity of Earth, the third-lowest in the system. Its radius and mass are also the third-least among the TRAPPIST-1 planets.

With both the radius and mass of TRAPPIST-1e determined with low error margins, scientists could accurately calculate the planet's density, surface gravity, and composition. Initial density estimates in 2018 suggested it has a density of 5.65 g/cm, about 1.024 times Earth's density of 5.51 g/cm. TRAPPIST-1e appeared to be unusual in its system, as it was the only planet with a density consistent with a pure rock-iron composition, and the only one with a higher density than Earth (TRAPPIST-1c also appeared to be entirely rock, but with a lower density than TRAPPIST-1e). The higher density of TRAPPIST-1e implies an Earth-like composition and a solid rocky surface. This also appeared to be unusual among the TRAPPIST-1 planets, as most were thought to have densities consistent with being completely covered in either a thick steam/hot CO₂ atmosphere, a global liquid ocean, or an ice shell. However, refined estimates show that all planets in the system have similar densities, consistent with rocky compositions, with TRAPPIST-1e having a somewhat lower but still Earth-like bulk density.

The planet has a calculated equilibrium temperature of 246.1 K (−27.1 °C; −16.7 °F) given an albedo of 0, also known as its "blackbody" temperature. For a more realistic Earth-like albedo however, this provides an unrealistic picture of the surface temperature of the planet. Earth's equilibrium temperature is 255 K; it is Earth's greenhouse gases that raise its surface temperatures to the levels we experience. If TRAPPIST-1e has a thick atmosphere, its surface could be much warmer than its equilibrium temperature.

Host star

The planet orbits an (late M-type) ultracool dwarf star named TRAPPIST-1. The star has a mass of 0.089 M_☉ – near the boundary between a brown dwarf and low-mass star – and a radius of 0.121 R_☉. It has a temperature of 2,516 K (2,243 °C; 4,069 °F) and is 7.6 billion years old. In comparison, the Sun is 4.6 billion years old and has a temperature of 5,778 K (5,505 °C; 9,941 °F). 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 0.0522% of that of the Sun.

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

Orbit

TRAPPIST-1e orbits its host star quite closely. One full revolution around TRAPPIST-1 takes only 6.099 Earth days (~146 hours) to complete. It orbits at a distance of 0.02928285 AU (4.4 million km; 2.7 million mi), or just under 3% the separation between Earth and the Sun. For comparison, the closest planet in the Solar System, Mercury, takes 88 days to orbit the Sun at a distance of 0.38 AU (57 million km; 35 million mi). Despite its close proximity to its host star, TRAPPIST-1e gets only about 60% the starlight that Earth gets from the Sun due to the low luminosity of its star. The star would cover an angular diameter of about 2.17 degrees from the surface of the planet, and so would appear about four times larger than the Sun does from Earth.

Atmosphere

TRAPPIST-1e is confirmed to not have a cloud-free hydrogen-dominated atmosphere, meaning it is more likely to have a compact, hydrogen-free atmosphere like those of the Solar System's rocky planets, further raising the chances of habitability. Hydrogen is a powerful greenhouse gas, so if there was enough to be easily detected, it would mean that the surface of TRAPPIST-1e would be inhospitable. Since such an atmosphere is not present, it raises the chances for the planet to have a more Earth-like atmosphere instead. However, no atmosphere has been detected, and it is still possible that the planet has no atmosphere at all. Additionally, no helium emission from TRAPPIST-1e was detected as of 2021.

Habitability

The exoplanet was announced to be orbiting within the habitable zone of its parent star, the region where, with the correct conditions and atmospheric properties, liquid water may exist on the surface of the planet. TRAPPIST-1e has a radius of around 0.91 R_🜨, so it is likely a rocky planet. Its host star is a red ultracool dwarf, with only about 8% of the mass of the Sun (close to the boundary between brown dwarfs and hydrogen-fusing stars). As a result, stars like TRAPPIST-1 have the potential to remain stable for up to 12 trillion years, which is over 2,000 times longer than the Sun. Because of this ability to live for such a long period of time, it is likely TRAPPIST-1 will be one of the last remaining stars in the Universe, when the gas needed to form new stars will be exhausted, and the existing stars begin to die off.

Other factors and 2018 studies

Despite being likely tidally locked – meaning one hemisphere permanently faces the star while the other does not – which may reduce the habitability of the planet, more detailed studies of TRAPPIST-1e and the other TRAPPIST-1 planets released in 2018 determined that the planet is in fact one of the most Earth-sized worlds found, with 91% the radius, 77% the mass, 102.4% the density (5.65 g/cm), and 93% the surface gravity. TRAPPIST-1e is confirmed to be a terrestrial planet with a solid, rocky surface. It is cool enough for liquid water to pool on the surface, but not so cold that it would freeze like on TRAPPIST-1f, g, and h.

The planet receives a stellar flux 60.4% that of Earth, about a third lower than that of Earth but significantly more than that of Mars. Its equilibrium temperature ranges from 225 K (−48 °C; −55 °F) to 246.1 K (−27.1 °C; −16.7 °F), depending on how much light the planet reflects into space. Both of these are between those of Earth and Mars as well. In addition, its atmosphere is confirmed to not be dense or thick enough to harm the habitability potential as well, according to models by the University of Washington. The atmosphere, if it is dense enough, may also help to transfer additional heat to the dark side of the planet.

2024 studies

According to a 2024 study, based on modeling, TRAPPIST-1e could be having its atmosphere stripped by its host star, possibly as a result of its short orbital period, which would make it inhospitable to life. The same phenomenon could impact the atmospheres of the other planets in this system. As of April 2024, it is not yet known whether TRAPPIST-1e has an atmosphere based on observation.

Future observations

As it is one of the most promising potentially habitable exoplanets known, TRAPPIST-1e was an early target of the James Webb Space Telescope in a research program led by Nikole Lewis. Launched on 25 December 2021, the telescope allows more extensive analysis of the planet's atmosphere, facilitating the search for any chemical signs of life, or biosignatures.

Discovery

A team of astronomers headed by Michaël Gillon used the TRAPPIST (Transiting Planets and Planetesimals Small Telescope) telescope at the La Silla Observatory in the Atacama Desert, Chile, to observe TRAPPIST-1 and search for orbiting planets. By utilising transit photometry, they discovered three Earth-sized planets orbiting the dwarf star; the innermost two are tidally locked to their host star while the outermost appears to lie either within the system's habitable zone or just outside of it. The team made their observations from September–December 2015 and published its findings in the May 2016 issue of the journal Nature.

The original claim and presumed size of the planet was revised when the full seven-planet system was revealed in 2017:

"We already knew that TRAPPIST-1, a small, faint star some 40 light years away, was special. In May 2016, a team led by Michaël Gillon at Belgium’s University of Liege announced it was closely orbited by three planets that are probably rocky: TRAPPIST-1b, c and d ...

"As the team kept watching shadow after shadow cross the star, three planets no longer seemed like enough to explain the pattern. "At some point we could not make sense of all these transits," Gillon said.

"Now, after using the space-based Spitzer telescope to stare at the system for almost three weeks straight, Gillon and his team have solved the problem: TRAPPIST-1 has four more planets.

"The planets closest to the star, TRAPPIST-1b and c, are unchanged. But there's a new third planet, which has taken the d moniker, and what had looked like d before turned out to be glimpses of e, f, and g. There's a planet h, too, drifting farthest out, and only spotted once."

Gallery

Videos

• Video (01:32) – Artistic representation of TRAPPIST-1 exoplanets transiting their host star.
• Video (01:10) – Fly-around animation of the planets of the TRAPPIST-1 system, including TRAPPIST-1e.

See also

• List of extrasolar candidates for liquid water
• List of potentially habitable exoplanets
• List of transiting exoplanets

References

1. ^ Gillon, Michaël; Triaud, Amaury H.M.J.; et al. (23 February 2017). "Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1". 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; et al. (21 January 2018). "The nature of the TRAPPIST-1 exoplanets". Astronomy & Astrophysics. 613 (A68). 21. arXiv:1802.01377. Bibcode:2018A&A...613A..68G. doi:10.1051/0004-6361/201732233. S2CID 3441829. Retrieved 7 November 2022.
4. van Grootel, Valerie; Fernandes, Catarina S.; et al. (5 December 2017). "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. ^ Gillon, Michaël; Jehin, Emmanuël; et al. (2 May 2016). "Temperate Earth-sized planets transiting a nearby ultracool dwarf star". Nature. 533 (7602): 221–224. arXiv:1605.07211. Bibcode:2016Natur.533..221G. doi:10.1038/nature17448. PMC 5321506. PMID 27135924.
7. NASA (21 February 2017). "NASA telescope reveals largest batch of Earth-size, habitable-zone planets around single star". NASA.gov. Retrieved 22 February 2017.
8. NASA; Jet Propulsion Laboratory (22 February 2017). "TRAPPIST-1 Planet Lineup". NASA's Jet Propulsion Laboratory (JPL). NASA. Retrieved 7 November 2022.
9. ^ Delrez, Laetitia; Gillon, Michael; et al. (9 January 2018). "Early 2017 observations of TRAPPIST-1 with Spitzer". Monthly Notices of the Royal Astronomical Society. 475 (3): 3577. arXiv:1801.02554. Bibcode:2018MNRAS.475.3577D. doi:10.1093/mnras/sty051. S2CID 54649681. Retrieved 7 November 2022.
10. ^ de Wit, Julien; Wakeford, Hannah R.; et al. (5 February 2018). "Atmospheric reconnaissance of the habitable-zone Earth-sized planets orbiting TRAPPIST-1". Nature Astronomy. 2 (3). Nature: 214–219. arXiv:1802.02250. Bibcode:2018NatAs...2..214D. doi:10.1038/s41550-017-0374-z. S2CID 119085332. Retrieved 7 November 2022.
11. Kelley, Peter (21 November 2018). "Study brings new climate models of small star TRAPPIST 1's seven intriguing worlds". EurekAlert!. University of Washington. Retrieved 22 November 2018.
12. "The Habitable Exoplanets Catalog". Planetary Habitability Laboratory @ UPR Arecibo (phl.upr.edu). University of Puerto Rico at Arecibo. 6 December 2021. Retrieved 6 February 2019.
13. "Equilibrium Temperatures of Planets". burro.case.edu. n.d. Retrieved 7 November 2022.
14. Williams, Matt (22 December 2015). "What is the Life Cycle Of The Sun?". Universe Today. Retrieved 7 November 2022.
15. Cain, Fraser (8 October 2013). "What Color is the Sun?". Universe Today. Retrieved 7 November 2022.
16. Krishnamurthy, Vigneshwaran; Hirano, Teruyuki; et al. (2 August 2021). "Nondetection of Helium in the Upper Atmospheres of TRAPPIST-1b, e, and f*". The Astronomical Journal. 162 (3): 82. arXiv:2106.11444. Bibcode:2021AJ....162...82K. doi:10.3847/1538-3881/ac0d57.
17. Adams, Fred C.; Laughlin, Gregory; Graves, Genevieve J.M. (December 2004). "Red Dwarfs and the End of the Main Sequence". Gravitational Collapse: From massive stars to planets. Vol. 22. Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias). pp. 46–49. Bibcode:2004RMxAC..22...46A.
18. Mendez, Abel (2021). "HEC: Exoplanets Calculator". Planetary Habitability Laboratory @ UPR Arecibo. University of Puerto Rico at Arecibo. Archived from the original on 18 October 2021. Retrieved 7 November 2022.
19. Cohen, Ofer; Glocer, Alex; et al. (February 2024). "Heating of the Atmospheres of Short-orbit Exoplanets by Their Rapid Orbital Motion through an Extreme Space Environment". The Astrophysical Journal. 962 (2): 157. arXiv:2401.14459. Bibcode:2024ApJ...962..157C. doi:10.3847/1538-4357/ad206a.
20. Robert Lea (28 February 2024). "Possibly habitable Trappist-1 exoplanet caught destroying its own atmosphere". Space.com. Retrieved 1 April 2024.
21. Jenner, Lynn, ed. (5 February 2020). "NASA's Webb Will Seek Atmospheres around Potentially Habitable Exoplanets". NASA.gov. NASA. Retrieved 7 November 2022.
22. Michaël Gillon is part of the Institut d'Astrophysique et Géophysique at the University of Liège: "AGO - Department of Astrophysics, Geophysics and Oceanography". ago.ulg.ac.be. Belgium: University of Liège. Retrieved 7 November 2022.
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v t e Exoplanets
Planet Definition IAU Planetary science
Main topics	Exoplanet Exoplanet orbital and physical parameters Methods of detecting exoplanets Planetary system Planet-hosting stars
Sizes and types	Terrestrial Carbon planet Coreless planet Desert planet Dwarf planet Hycean planet Ice planet Iron planet (Super-Mercury) Lava planet Ocean world Mega-Earth Sub-Earth Super-Earth Gaseous Eccentric Jupiter Mini-Neptune (Gas dwarf) Helium planet Hot Jupiter Hot Neptune Gas giant Ice giant Super-Jupiter Super-Neptune Super-puff Ultra-hot Jupiter Ultra-hot Neptune Other types Blanet Brown dwarf Chthonian planet Circumbinary planet Circumtriple planet Disrupted planet Double planet Ecumenopolis Eyeball planet Giant planet Mesoplanet Planemo Planet/Brown dwarf boundary Planetesimal Protoplanet Pulsar planet Sub-brown dwarf Sub-Neptune Toroidal planet Ultra-cool dwarf Ultra-short period planet (USP)
Formation and evolution	Accretion Accretion disk Asteroid belt Circumplanetary disk Circumstellar disc Circumstellar envelope Cosmic dust Debris disk Detached object Disrupted planet Excretion disk Exozodiacal dust Extraterrestrial materials Extraterrestrial sample curation Giant-impact hypothesis Gravitational collapse Hills cloud Internal structure Interplanetary dust cloud Interplanetary medium Interplanetary space Interstellar cloud Interstellar dust Interstellar medium Interstellar space Kuiper belt List of interstellar and circumstellar molecules Merging stars Molecular cloud Nebular hypothesis Oort cloud Outer space Planetary migration Planetary system Planetesimal Planet formation Protoplanetary disk Ring system Rubble pile Sample-return mission Scattered disc Star formation
Systems	Exocomet Interstellar Exomoon Tidally detached Rogue planet Orbits Retrograde Trojan Mean-motion resonances Titius–Bode law
Host stars	A B Binary star Brown dwarfs F/Yellow-white dwarfs G/Yellow dwarfs Herbig Ae/Be K/Orange dwarfs M/Red dwarfs Pulsar Red giant Subdwarf B Subgiant T Tauri White dwarfs Yellow giants
Detection	Astrometry Direct imaging list Microlensing list Polarimetry Timing list Radial velocity list Transit method list Transit-timing variation
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
Catalogues	Nearby Habitable Systems Exoplanet Data Explorer Extrasolar Planets Encyclopaedia NASA Exoplanet Archive NASA Star and Exoplanet Database Open Exoplanet Catalogue
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
Discoveries of exoplanets Search projects

v t e 2017 in space
« 2016 2018 »
Space probe launches	ASTERIA (miniature space telescope; August 2017)
Impact events	Bolides in 2017 2017 China bolide
Selected NEOs	Asteroid close approaches 2017 AG13 2017 BS5 2017 BQ6 2016 WF9 2014 JO25 2017 OO1 2017 QP1 3122 Florence 2017 SX17 2012 TC4 2017 TD6 2017 VL2 2017 VW13 2017 XO2 3200 Phaethon
Exoplanets	HATS-36b HD 113996 b KELT-18b Kepler-19d Kepler-80g Kepler-90i K2-66b K2-138b LHS 1140 b Luyten b NGTS-1b OGLE-2016-BLG-1190Lb OGLE-2016-BLG-1195Lb Ross 128 b Tau Ceti g h TRAPPIST-1 e f g h dark albedo of WASP-12b WASP-107b YZ Ceti b c d
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Comets	C/2016 U1 (NEOWISE) 41P/Tuttle–Giacobini–Kresák 103P/Hartley C/2015 ER61 (PanSTARRS) C/2015 V2 (Johnson) P/2006 VW139 C/2017 O1 (ASASSN) 96P/Machholz
Space exploration	Cassini retirement (impacted into Saturn; Sep 2017) OSIRIS-REx (Earth gravity assist; Sep 2017)
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

• Biology
• Science
• Stars
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• Solar System

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