A radioactive, silvery metal.Plutonium was used in several of the first atomic bombs, and is still used in nuclear weapons. The complete detonation of a kilogram of plutonium produces an explosion equivalent to over 10,000 tonnes of chemical explosive.Plutonium is also a key material in the development of nuclear power. It has been used as a source of energy on space missions, such as the Mars Curiosity Rover and the New Horizons spacecraft on its way to Pluto.