This artist's visualization depicts a water world exoplanet, with an atmosphere and jet streams encircling it. An exoplanet is any identified planet outside of our own Solar System. As of June 2013, there have been 866 exoplanets identified, located around 671 stars, nearly all within the Milky Way Galaxy. Large patches of clouds can also be seen. Kepler-22b has an estimated mass of 36 Earth masses and a radius of 2.38 Earth radii, making it a "super-Earth." It is an ocean planet instead of having a rocky, Earth-like composition. Assuming that an atmosphere with thermal properties similar to Earth's is present, and one without the high-temperature greenhouse effect of Venus, an average surface temperature of 21 C (70 F) has been calculated.
Kepler-22b is located 620 light years away in the constellation of Cygnus. It has an orbital period of 290 days. Kepler-22b was the first of the Kepler planets to be found in the habitable zone of its host star. The habitable zone is the region in which liquid water could exist on a planet's surface. Liquid water is a key ingredient to life, so planets found within this zone are more likely to be habitable worlds. However, planets must also be the right size, and Kepler-22b is too big.
Launched in 2009, the Kepler spacecraft measures the light output of 150,000 stars simultaneously. The data from each star is then analyzed in order to look for periodic drops in the light curve being emitted. These drops in brightness could indicate the presence of an orbiting planet passing in front of its host star, blocking some of its light. This is called a transit. Three or more transits of equal periods are needed to catalog an object as an exoplanet candidate.