Kepler-22b

Kepler-22b, also known by its Kepler object of interest designation KOI-087.01, is an extrasolar planet orbiting within the habitable zone of the Sun-like star Kepler-22. It is located about 587 light-years (180 pc) 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. Kepler-22 is too dim to be seen with the naked eye. Kepler-22b's size is roughly twice that of Earth. Its mass and surface composition are unknown. 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, which is about 290 days, and its inclination, which is 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), compared to Earth's 255 K (−18 °C) The planet's first transit was observed on 12 May 2009. Confirmation of the existence of Kepler-22b was announced on 5 December 2011. Kepler-22b is an extrasolar planet orbiting around the star Kepler-22. It is about 587 light-years (180 pc) from Earth in the constellation of Cygnus. It was discovered by the Kepler Space Telescope in December 2011. Kepler-22b's radius is roughly 2.4 times that of Earth. Its mass and surface composition remain unknown, with only some very rough estimates established: it has fewer than 124 Earth masses at the 3-sigma confidence limit, and fewer than 36 Earth masses at 1-sigma confidence. The adopted model in Kipping et al. (2013) does not reliably detect the mass (the best fit value is only slightly larger than the 1-sigma error bar), though the mass is below 52.8 Earth masses to 95% confidence. Kepler-22b, dubbed by scientists as a 'waterworld', might be an 'ocean-like' planet. It might also be comparable to the water-rich planet GJ 1214 b although Kepler-22b, unlike GJ 1214 b, is in the habitable zone. An Earth-like composition is ruled out to at least 1-sigma uncertainty by radial velocity measurements of the system. It is thus likely to have a more volatile-rich composition with a liquid or gaseous outer shell; this would make it similar to Kepler-11f, the smallest known gas planet. Natalie Batalha, one of the scientists on the Kepler Space Telescope project, has speculated, 'If it is mostly ocean with a small rocky core, it's not beyond the realm of possibility that life could exist in such an ocean'. This possibility has spurred SETI to perform research on top candidates for extraterrestrial life. The host star, Kepler-22, is a G-type star that is 3% less massive than the Sun and 2% smaller in volume. It has a surface temperature of 5,518 K (5,245 °C) compared with the Sun, which has a surface temperature of 5,778 K (5,505 °C). The star is about 4 billion years old. In comparison, the Sun is 4.6 billion years old. The apparent magnitude of Kepler-22 is 11.5, which means it is too dim to be seen with the naked eye.