radioactive heating

Radioactive heating (aka radiogenic heating) is heating due to radioactive decay, i.e., emission of alpha rays, beta rays, or gamma rays, from unstable isotopes. It can be a significant source of heat within planets and moons, including Earth and the Moon. The mechanism has also been used as a spacecraft energy-source by carrying some radioactive material within a device that converts the heat into electricity. Regarding Earth, it is theorized to be sufficiently significant to constitute one key to Earth's active geology, plate tectonics, and habitability.