From Al Fin:
The latest NASA Mars rover, Curiosity, is a monster in comparison to earlier Mars explorer robots. Thus it has a monster-sized appetite for energy which solar power simply could not guarantee. Thus NASA Curiosity opted for nuclear power -- the smart choice for reliable energy.
The nuclear generator delivers both heat and 110 watts of steady electric power from an array of iridium capsules holding a ceramic form of plutonium dioxide. The heat is piped through the Curiosity carried by liquid Freon. Thermoelectric devices on the generator convert the heat into electricity with no moving parts. Idaho National Laboratory, which designed and tested the energy system, says it can operate for years. _TechnologyReview