"In later episodes, Mumm-Ra magically reconstructs Thundera in order to gain the Sword of Plun-Darr and locate the Treasure of Thundera, which harbors the ThunderCats' secrets. In these episodes, the ThunderCats' adventures alternate between New Thundera and Third Earth. Eventually, the ThunderCats return to New Thundera to rebuild their society, while still maintaining guard duty on Third Earth." (http://en.wikipedia.org/wiki/Thundercats )