Brian Cox on discovery of planet Kepler 22-b
6 December 2011 Last updated at 16:30 GMT
TV scientist Prof Brian Cox told Radio 5 live's Richard Bacon about the significance of discovering the Earth-like planet.
Nasa confirmed the existence of Kepler 22-b, which is 600 light years away and has a surface temperature of 22C (71.6F).
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Richard Bacon broadcasts weekdays 1400 to 1600 on Radio 5 live.