There is nuclear energy transformations inside planets that creates lots of energy: http://physicsworld.com/cws/article/news/2011/jul/19/radioactive-decay-acco

There is nuclear energy transformations inside planets that creates lots of energy: http://physicsworld.com/cws/article/news/2011/jul/19/radioactive-decay-accounts-for-half-of-earths-heat http://physicsworld.com/cws/article/news/2011/jul/19/radioac...