Gliese 581 g is a planet orbiting the red dwarf star Gliese 581, approximately 20.5 light-years away from Earth in the constellation of Libra. It is the sixth planet discovered in the Gliese 581 planetary system and the fourth in order from the star.
The planet is believed to have a mass of 3.1 to 4.3 times that of the Earth and a radius of 1.3 to 2 times that of Earth. It has an orbital period of just under 37 days, orbiting at a distance of 0.146 AU from its parent star.
Despite the presence of other planets between Gliese 581 g and the parent star that are not tidally locked, the planet is at the right distance to be tidally locked to Gliese 581 due to its size, just as our moon always presents the same face to the Earth; the length of Gliese 581 g's sidereal day would then precisely match the length of its year.
Theoretical models predict that volatile compounds such as water and carbon dioxide, if present, might evaporate in the scorching heat of the sunward side, migrate to the cooler night side, and condense to form ice caps. Over time, the entire atmosphere might freeze into ice caps on the night side of the planet. Alternatively, an atmosphere large enough to be stable would circulate the heat more evenly, allowing for a wider habitable area on the surface.
Source : wikipedia
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