Source of Power

Explanation: A glowing cylinder of 238PuO2. The isotope plutonium-238 has a half-life of 87.74 years and emits a large amount of thermal energy, making it well-suited for electrical power generation for devices which must function without direct maintenance for timescales approximating a human lifetime. It is therefore used in radioisotope thermoelectric generators and radioisotope heater units such as those on the Voyager, Cassini, and New Horizons spacecraft.

Pluto

Image credit: Department of Energy.