Kepler-22b

Kepler-22b (also known by its Kepler object of interest designation KOI-087.01) is an exoplanet orbiting the Sun-like star Kepler-22 within its habitable zone. It is located about 640 light-years (200 parsecs) from Earth in the constellation Cygnus. Discovered by NASA's Kepler space telescope, it was announced on 5 December 2011 as the first known transiting planet to orbit within the habitable zone of a Sun-like star, where conditions could allow liquid water to exist on the surface. Kepler-22b has a radius about twice that of Earth. Its mass and surface composition are unknown, but an Earth-like composition is considered unlikely. It may instead be an ocean planet or have a volatile-rich composition with a liquid or gaseous outer layer. The planet's known orbital parameters are its orbital period, about 290 days, and its inclination, approximately 90°. Its surface temperature may be moderate if it does not experience extreme greenhouse heating. In the absence of an atmosphere, its equilibrium temperature, assuming an Earth-like albedo, would be about 279 K (6 °C; 43 °F), slightly higher than Earth's equilibrium temperature of 255 K (−18 °C; −1 °F).