Kepler-22b (also known by its Kepler object of interest designation KOI-087.01) is an exoplanet orbiting within the habitable zone of the Sunlike star Kepler-22. It is located about 600 light-years (180 parsecs) from Earth in the constellation of Cygnus. It was discovered by NASA's Kepler Space Telescope in December 2011 and was the first known transiting planet to orbit within the habitable zone of a Sun-like star, where liquid water could exist on the planet's surface. Kepler-22 is too dim to be seen with the naked eye.
Kepler-22b's radius is roughly twice that of Earth. Its mass and surface composition are unknown. However, an Earth-like composition for the planet has been ruled out; it is likely to have a volatile-rich composition with a liquid or gaseous outer shell. The only parameters of the planet's orbit that are currently available are its orbital period (about 290 days) and its inclination (approximately 90°). Evidence suggests that the planet has a moderate surface temperature, assuming that the surface is not subject to extreme greenhouse heating. In the absence of an atmosphere, its equilibrium temperature (assuming an Earth-like albedo) would be approximately 262 K (−11 °C; 12 °F), compared with Earth's 255 K (−18 °C; −1 °F).
The planet's first transit was observed on 12 May 2009. Confirmation of the existence of Kepler-22b was announced on 5 December 2011.