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TRAPPIST-1g

TRAPPIST-1g

Artist's impression of TRAPPIST-1g. (February 2018)
Discovery[1]
Discovered by	Michaël Gillon et al.
Discovery site	Spitzer Space Telescope
Discovery date	22 February 2017
Detection method	Transit
Orbital characteristics[2]
Semi-major axis	0.04683±0.00040 AU
Eccentricity	0.00208±0.00058[3]
Orbital period (sidereal)	12.352446±0.000054 d
Inclination	89.742°±0.012°
Argument of periastron	191.34°±13.83°[3]
Star	TRAPPIST-1[4]
Physical characteristics[2]
Mean radius	1.129+0.015 −0.013 R🜨
Mass	1.321±0.038 M🜨
Mean density	5.042+0.136 −0.158 g/cm3
Surface gravity	1.035±0.026 g 10.15±0.25 m/s2
Temperature	Teq: 197.3±1.9 K (−75.8 °C; −104.5 °F)[5]

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.^[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]

Physical characteristics[edit]

Mass, radius, and temperature[edit]

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,^[2] though initial estimates suggested its density was only 4.186 g/cm³, about 76% of Earth's.^[3] 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.^[8]

Atmosphere[edit]

TRAPPIST-1g could have a global water ocean or an exceptionally thick steam atmosphere.^[3] 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.^[9]

On 31 August 2017, astronomers at the Hubble Space Telescope reported the first evidence of possible water content on the TRAPPIST-1 exoplanets.^[10][11][12]

Host star[edit]

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.^[13] 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[edit]

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[edit]

• 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[edit]

Biology

Space