From the BBC:
The planet, Kepler 22-b, lies about 600 light-years away and is about 2.4 times the size of Earth, and has a temperature of about 22C.
It is the closest confirmed planet yet to one like ours – an “Earth 2.0”.
However, the team does not yet know if Kepler 22-b is made mostly of rock, gas or liquid.
During the conference at which the result was announced, the Kepler team also said that it had spotted some 1,094 new candidate planets – nearly doubling the telescope's haul of potential far-flung worlds.
Kepler 22-b was one of 54 exoplanet candidates in habitable zones reported by the Kepler team in February, and is just the first to be formally confirmed using other telescopes.