|Extrasolar planet||List of extrasolar planets|
A diagram of the Kepler-22b System, compared to our Inner Solar System.
|Right ascension||(α)||19h 16m 52.2s|
|Declination||(δ)||+47° 53′ 4.0″|
|Apparent magnitude||(mV)||11.5 (B-band) |
(190  pc)
|Semimajor axis||(a)||0.85 AU
|Orbital period||(P)||289.9  d|
|Radius||(r)||2.4  R⊕|
|Discovery date||2009 (first observed)
12/5/2011 (announced) 
|Discoverer(s)||Kepler Science Team|
|Discovery site||Kepler telescope|
Kepler-22b is the first confirmed extrasolar planet found by NASA‘s Kepler Space Telescope to orbit within the habitable zone of a Sun-like star. Kepler-22b, a possible super-Earth, is 600 light years away from Earth, in orbit around Kepler-22, a G-type star.
||This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may bechallenged and removed. (January 2012)|
The discovery was announced December 5, 2011. The planet was originally discovered on Kepler’s third day of science operations in mid-2009. The third transit was detected in late 2010. Additional confirmation data was provided by the Spitzer Space Telescope and ground-based observations.
Composition and structure
Kepler-22b’s radius is roughly 2.4 times the radius of Earth, or about 60% that of Neptune. Its mass and surface composition remain unknown, with only some very rough estimates established: It has less than 124 Earth masses at the 3 sigma confidence limit, and less than 36 Earth masses at 1 sigma confidence.
It has been estimated that it is probably a “Neptunian” (i.e. mass similar to Neptune) planet with a mass of ~35 Earth masses, but there is the possibility it could be an “ocean like” world with only some 10 Earth masses. It might be comparable to GJ 1214 b, whose radius is similar to Kepler-22b’s.
Since it is substantially larger than our planet, it is likely to have a different composition than Earth, and depending on its actual mass, the planet could be rocky, liquid, or gaseous.. If it is mostly ocean with a small rocky core, Natalie Batalha, one of the scientists on the project, speculated “it’s not beyond the realm of possibility that life could exist in such an ocean.” This possibility of life has spurred SETI to perform research on top candidates for extraterrestrial intelligence.
The only parameters of the planet’s orbit that are currently available are its period, which is about 290 days, and its inclination, which is such that it transits the disk of its star as seen from Earth.
No information is available about the shape of the planet’s orbit. Many extrasolar planets are known to move in highly elliptical orbits. We only know that the semi-major axis of its orbit is within the habitable zone of an Earth mass planet. If Kepler-22b has a highly elongated orbit it may well only spend a small fraction of its time within this habitable zone.
Surface temperature and composition
The average distance from Kepler-22b to its host star Kepler-22 is about 15% less than the distance from Earth to the Sun but the luminosity (light output) of Kepler-22 is about 25% less than that of the Sun. This combination of a shorter average distance from the star and a lower stellar luminosity are consistent with a moderate surface temperature at that distance if we assume that the surface is not subject to extreme greenhouse heating.
If the planet is found to move in a highly elliptical orbit, its surface temperature will vary from a higher temperature when close to Kepler-22 to lower when further away. If the orbit is indeed highly elliptical, then the temperature variance range will be extreme.
Scientists can estimate the possible surface conditions as follows:
- In the absence of an atmosphere, the equilibrium temperature would be approximately -11°C.
- If the atmosphere provides a greenhouse effect similar in magnitude to the one on Earth, the planet would have an average surface temperature of 22 °C (72°F).
- If the atmosphere has a greenhouse effect similar in magnitude to the one on Venus, the planet would have an average surface temperature of 460 °C (860°F).