TRAPPIST-1g

TRAPPIST-1g

Artist's impression of TRAPPIST-1g. (February 2018)
Discovery
Discovery date	2017
Detection method	Transit
Orbital characteristics
Semi-major axis	0.0451 (± 0.0014) AU
Eccentricity	0.0 ( −0.0 +0.061 )
Orbital period (sidereal)	12.35294 (± 0.00012) Juliean d
Inclination	100.2 (± 0.025)
Star	TRAPPIST-1
Physical characteristics
Mean radius	0.1005 (± 0.0037) RJ 1.127 ± 0.041 R🜨
Mass	1.34 ME
Mean density	5.18 ± 3.48 g cm−3
Surface gravity	~10.35 m/s²
Temperature	198.6 ± 3.8 K

TRAPPIST-1g, also designated as 2MASS J23062928-0502285 g, is an exoplanet orbiting around the ultra-cool dwarf star TRAPPIST-1 39 light-years (12 parsecs) away from Earth in the constellation Aquarius. It was one of four new exoplanets to be discovered orbiting the star using observations from the Spitzer Space Telescope. The exoplanet is within the habitable zone. 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.

Characteristics

Mass, radius, and temperature

TRAPPIST-1g is an Earth-sized exoplanet, meaning it has a mass and radius close to that of Earth. It has an equilibrium temperature of 198.6 K (−75 °C; −102 °F). This planet has a mass of 1.34 M_⊕ and a radius of 1.13 R_⊕, resulting in an estimated surface gravity of 10.3 m/s² and a density of 5.13 g/cm³, both similar to Earth.

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 and is at least 500 million years old. 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 12.353 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 habitable zone. The orbit of TRAPPIST-1g has an eccentricity of 0.003, much lower than that of Earth and similar to that of TRAPPIST-1e. Its orbit varies by only about 41,000 kilometers (compared to about 5 million km for Earth), probably making the planet's climate very stable. It is in a 3:2 orbital resonance with TRAPPIST-1h and a 3:4 resonance with TRAPPIST-1f.

Water

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

See also

• List of extrasolar candidates for liquid water
• List of transiting exoplanets
• List of potentially habitable exoplanets
• List of nearest terrestrial exoplanet candidates
• Other Habitable Zone planets of the TRAPPIST-1 system:
  • TRAPPIST-1d
  • TRAPPIST-1e
  • TRAPPIST-1f