Plutonium is a radioactive metal created artificially in laboratories and nuclear reactors. Scientists discovered it in 1940 by bombarding uranium with neutrons (tiny particles in atoms). Unlike most elements, which exist naturally in Earth's crust, plutonium must be manufactured through nuclear reactions.

The element gets its name from Pluto, the dwarf planet at the edge of our solar system. Scientists chose this name to continue a pattern: uranium was named for Uranus, neptunium for Neptune, and then plutonium for Pluto. At the time, astronomers still considered Pluto a full planet.

Plutonium became famous, and infamous, for two main uses. First, it powers certain nuclear reactors that generate electricity. A piece of plutonium the size of a marble contains as much energy as hundreds of gallons of gasoline. Second, it was used to make nuclear weapons during World War II and the Cold War. The atomic bomb dropped on Nagasaki, Japan, in 1945 used plutonium as its explosive core.

The metal is extraordinarily dangerous. It remains radioactive for thousands of years, emitting invisible rays that can harm living cells. Scientists handle plutonium using remote controls and thick protective barriers. A speck smaller than a grain of sand would be toxic if inhaled.

Today, plutonium exists mostly in secured facilities where scientists study it for peaceful energy research or where governments carefully store material from old nuclear weapons.