The stunning pictures of Neptune being transmitted to Earth from the Voyager 2 spacecraft are coming courtesy of an unusual form of nuclear power that runs the craft's cameras, computers and radio transmitters that beam the pictures over.

The Voyager's designers knew the craft would fly so far from the Sun that solar-electric cells would be virtually useless. To create electricity in the void, they instead relied on a small type of nuclear generator that turns the heat of decaying plutonium-238 into electric power.

This energy source is not that of a nuclear reactor, in which atoms are actively broken apart, but rather a kind of nuclear battery that uses natural radioactive decay to produce power.

Voyager 2 uses three of these radioisotope thermionic generators. In them, the heat from decaying plutonium, applied to metal strips, generates a flow of electrons. The device has with no moving parts, no flow of fluids and no turbines. The three units are now producing about 375 watts of electricity to power all the spacecraft's systems. This amount of current is far less than a kitchen toaster or a hair dryer require. Perfectly Working Units