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TRAPPIST-1h, also known as 2MASS J23062928-0502285 h, is a terrestrial extrasolar planet orbiting around the ultra-cold dwarf star TRAPPIST-1, located approximately 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.

Characteristics[]

Mass, radius, and temperature[]

TRAPPIST-1h is an Earth-sized exoplanet, meaning it has a mass and radius close to that of Earth. Like TRAPPIST-1d, it is intermediate between the sizes of Mars and Earth. The amount of light blocked by the host star shows that TRAPPIST-1h is 0.715 Earth radii. Transit Timing Variations also give a mass of around 0.086 ± 0.084 Earth masses. These two values make TRAPPIST-1h the smallest of all the planets in its system. The planet's density is around 1.297 ± 1.266 g/cm3 with a gravity only around 0.168 times that of Earth, similar to the gravitational pull of the Moon. It has an equilibrium temperature of 169 K (-104 °C; -155 °F), similar to that of Earth's south pole.

Host star[]

The planet orbits an (late M-type) ultracool dwarf star named TRAPPIST-1. The star has a mass of 0.089 M☉ and a radius of 0.121 R☉. It has a temperature of 2516 K and is anywhere between 3 and 8 billion 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 0.0522% 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 too dim to be seen with the naked eye.

Orbit[]

TRAPPIST-1h orbits its host star with an orbital period of 18.764 days and an orbital radius of about 0.063 AU (compared to the distance of Mercury from the Sun, which is about 0.38 AU.

Might host water[]

Although TRAPPIST-1h is at the "snow line", it could harbor liquid water under an H2-rich atmosphere, either primordial or resulting from continuous outgassing combined with internal heating. If not, then it could harbor a subsurface ocean powered by underground volcanoes, if it is an icy planet.

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