TRAPPIST-1b

TRAPPIST-1b
Exoplanet List of exoplanets

Artist's impression of TRAPPIST-1b
Parent star
Star TRAPPIST-1[1]
Spectral type M8[1][2]:1236
Mass (m) 0.08 (± 0.009) (± 0.02)[1] M☉
Radius (r) 0.117 (± 0.004)[1] R☉
Temperature (T) 2550.0 (± 55.0)[1] K
Age 3–8[1] Gyr
Orbital elements
Semi-major axis(a) 0.01111 ± 0.00034[3] AU
Eccentricity (e) 0.019[3]
Orbital period(P) 1.510848 (± 1.9e-05)[1] d
Inclination (i) 89.41 (± 0.41)[1]°
Physical characteristics
Mass(m)0.79[3] M⊕
Minimum mass(m sin i)0.52[3] M⊕
Maximum mass(m sin i)1.06[3] M⊕
Radius(r)1.086 ± 0.035[3] R⊕
Stellar flux(F⊙)4.25 ± 0.33[3] ⊕
Density(ρ)3.401 ± 1.16 g cm−3
Surface gravity(g)~0.6689 g
Temperature (T) 400.1 ± 7.7[3]
Discovery information
Discovery date May 2, 2016
Discoverer(s)
Discovery method Transit
Discovery status Published

TRAPPIST-1b, also designated as 2MASS J23062928-0502285 b, is an exoplanet, possibly rocky, orbiting around the ultra-cold dwarf star TRAPPIST-1, located approximately 39 light-years (12 parsecs) away from Earth in the constellation Aquarius. The planet was detected using the transit method, where a planet dims the host star's light as it passes in front of it. It was first announced on May 2, 2016. On February 23, 2017, along with four new planets announced in the system, more accurate physical parameters for TRAPPIST-1b were determined.

Hubble Space Telescope observations on May 4, 2016, showed that planets b and c have compact, terrestrial atmospheres. TRAPPIST-1b and its sister planet are just two of three Earth-sized planets found to have atmospheres, the other being GJ 1132b.

Characteristics

Mass, radius, and temperature

TRAPPIST-1b is an Earth-sized planet, meaning that its radius and mass values are similar to that of Earth. The planet's radius is 1.086 times that of Earth, with an error of only about 223 kilometers. Its mass was determined by observing how the planet's mass affected the orbits of the other planets. These are known as transit timing variations. TTV data of the TRAPPIST-1 system shows that TRAPPIST-1b has a mass of about 0.86 times that of Earth; However, newer measurements have refined that value to 0.79±0.27 Earth masses. Using both the mass and radius, TRAPPIST-1b's density works out to be about 3.401±1.16 g/cm3, with its gravity being 66.89% that of Earth. The planet's mass and density are unusually low of an object of this radius, suggesting a composition with either little to no iron, or with a bulk of the mass made up of water (10–20%).

Due to its close proximity to its host star, TRAPPIST-1b is the hottest planet of the system. However, since TRAPPIST-1 is so dim, the planet's temperature is only around 400.1 K (126.95 °C, or 260.51 °F). This is cool enough for TRAPPIST-1b to retain a significant atmosphere, but too hot for life as we know it or liquid water, unless it is kept a liquid by atmospheric pressure.

Spectrum of TRAPPIST-1 b and c

The combined transmission spectrum of TRAPPIST-1 b and c rules out a cloud-free hydrogen-dominated atmosphere for each planet, so they are unlikely to harbor an extended gas envelope. Other atmospheres, from a cloud-free water-vapor atmosphere to a Venus-like atmosphere, remain consistent with the featureless spectrum.[4]

Habitability

During formation of the system it is possible that water loss during pre-HZ periods occurred.[5] It is estimated that TRAPPIST-1b and TRAPPIST-1c may have lost up to 15 Earth oceans worth of water, possibly compromising their habitability. However, TRAPPIST-1d and the other planets are likely to have been able to keep enough liquid water to sustain life, increasing the chances of these planets being potentially habitable.[5] In addition, the low density of TRAPPIST-1b suggests a composition made of up to 10–20% water, meaning that there would be too much to be completely evaporated, but the planet' high temperature would make it that all water is trapped in a super-critical state. Such hot water could make the genesis of life impossible.

  • Artist's view of planets transiting red dwarf star in TRAPPIST-1 system[6]
  • The Sun and the ultracool dwarf star TRAPPIST-1 to scale. The faint star has only 11% of the diameter of the Sun and is much redder in colour.
  • Artist's impression of the three planets orbiting TRAPPIST-1
  • Artist’s impression video, near one of the three planets orbiting TRAPPIST-1. One of the inner planets is shown in transit across the disc of its tiny and dim parent star.

References

  1. 1 2 3 4 5 6 7 8 "Planet TRAPPIST-1 b". Exoplanet.eu. Retrieved 2016-05-06.
  2. ↑ Costa, E.; Mendez, R. A.; Jao, W.-C.; Henry, T. J.; Subasavage, J. P.; Ianna, P. A. (August 4, 2006). "The Solar Neighborhood. XVI. Parallaxes from CTIOPI: Final Results from the 1.5 m Telescope Program" (PDF). The Astronomical Journal. The American Astronomical Society. 132 (3): 1234. Bibcode:2006AJ....132.1234C. doi:10.1086/505706.
  3. 1 2 3 4 5 6 7 8 Gillon, Michaël; Triaud, Amaury H. M. J.; Demory, Brice-Olivier; Jehin, Emmanuël; Agol, Eric; Deck, Katherine M.; Lederer, Susan M.; Wit, Julien de; Burdanov, Artem. "Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1". Nature. 542 (7642): 456–460. arXiv:1703.01424 Freely accessible. doi:10.1038/nature21360.
  4. ↑ de Wit, Julien; et al. (2016). "A combined transmission spectrum of the Earth-sized exoplanets TRAPPIST-1 b and c". Preprint. arXiv:1606.01103 Freely accessible.
  5. 1 2 Bolmont, Emeline; Selsis, Franck; Owen, James E.; Ribas, Ignasi; Raymond, Sean N.; Leconte, Jérémy; Gillon, Michael (2016). "Water loss from Earth-sized planets in the habitable zones of ultracool dwarfs: Implications for the planets of TRAPPIST-1". arXiv:1605.00616 Freely accessible [astro-ph.EP].
  6. ↑ "Artist's view of planets transiting red dwarf star in TRAPPIST-1 system". www.spacetelescope.org. Retrieved 21 July 2016.
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