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Kepler-42 c

KOI-961 c, KOI-961.02

Proper NameNone
DesignationsKepler-42 c, KOI-961 c, KOI-961.02
ClassificationEarth-mass planet
Orbital Period10 hours, 52 minutes
Mean Distance from Kepler-42898,000 km
0.01 AU
MassNot known
Diameter0.73 x Earth
TemperatureNot known
Parent starKepler-42, red dwarf in Cygnus
Other planets in this systemKepler-42 b, Earth-mass planet
Kepler-42 d, Earth-mass planet

The innermost of three rocky planets orbiting the red dwarf star Kepler-42. The system is some 131 light years from the Solar System, and lies within the western boundaries of Cygnus, near that constellation's border with Lyra. Kepler-42 is a tiny red star, just 0.13 the mass of the Sun and less than a fifth its diameter. Its system of three planets was discovered in 2012.

Imagery provided by Aladin sky atlas

All three planets occupy very close orbits around the star, with even the outer planet, Kepler-42 d, averaging a distance of just 0.015 AU. Kepler-42 c is the innermost of the three, orbiting the red dwarf at just 0.006 AU (only a little more than twice the distance from the Earth to the Moon).

Kepler-42 c is a rocky terrestrial planet, like all three members of its system. Its maximum mass is roughly twice that of Earth, though it seems to be rather smaller in terms of diameter. Its extremely close orbit to its parent star means that the planet is very hot, with surface temperatures estimated to exceed 450° Celsius. Kepler-42 c is tidally locked to the red dwarf star, meaning that one side is permanently baked by the star's heat, while the other side of the planet remains in permanent shadow.