Plutonium is the sixth and most infamous member of the actinides located on the second row below the periodic table. It is a silvery-white, radioactive metal with a melting point of 639 degrees Celsius. It was discovered in 1940 by Glenn T. Seaborg and his team. It is a brittle,  reactive metal that quickly forms oxides on exposure to air. Plutonium 239 has a half-life of 24100 years. Plutonium is extremely rare on Earth. It is created in supernovae, but most Plutonium on Earth has already decayed.  

This element is notoriously used in nuclear weapons. The bomb that went off on Nagasaki was a Plutonium bomb. Some of its more positive uses are as a power source for spacecraft and rovers.