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. The planet’s radius is roughly 2.4 times the radius of Earth; it is 600 light years away from Earth, in orbit around the G-type star Kepler 22.
Composition and structure
To date, its mass and surface composition remain unknown. If it has an Earth-like density (5.515 g/cm3) then it would contain 13.8 Earth masses, while its surface gravity would be 2.4 times Earth’s. If it has water-like density (1 g/cm3) then it would mass 2.5 Earths and have a surface gravity of 0.43 times Earth’s. The planet may fall into the category of planets known as super-Earths, depending on what the actual mass is.
Possibility of life
The distance from Kepler-22b to its host star is about 15% less than the distance from Earth to the Sun, but the luminosity (light output) of Kepler-22b’s star is about 25% less than that of the Sun. This combination of a shorter distance from the star and a lower stellar luminosity are consistent with a moderate surface temperature. Scientists estimate that 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).
What NASA Say..
The centuries-old quest for other worlds like our Earth has been rejuvenated by the intense excitement and popular interest surrounding the discovery of hundreds of planets orbiting other stars.
Astronomers have discovered sizable numbers of gas and ice giants like Jupiter and Neptune and even super-earth-size planets in short-period orbits around their parent star. The following websites track the day-by-day increase in new discoveries and are provide information on the characteristics of the planets as well as those of the stars they orbit: Extrasolar Planets Encyclopedia, Exoplanet Data Explorer, New Worlds Atlas, and Current Planet Count Widget.
The challenge now is to find terrestrial planets (i.e., those one half to twice the size of the Earth), especially those in the habitable zone of their stars where liquid water and possibly life might exist.
The Kepler Mission, NASA Discovery mission #10, is specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size and smaller planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets.
Results from this mission will allow us to place our solar system within the continuum of planetary systems in the Galaxy.
(Information attained from Wikipedia & NASA)