Kepler-22b\'s Earth Similarity index is estimated to be between 0.64 and 0.79. Earth is, of course, 1. Mars is 0.70, and Mercury is 0.60. However, one candidate object observed by kepler but unconfirmed is KOI 736.01, with a rating of 0.98. Source is wikipedia so take all of this with a large grain of salt.