Neptunium is the fifth member of the actinides located on the second row below the periodic table. It is a silvery, radioactive metal with a melting point of 637 degrees Celsius. It was discovered in 1940 by Edwin McMillan and Philip Abelson. It is a reactive metal that quickly forms oxides on exposure to air. Neptunium 237 has a half life of 2.14 million years. Neptunium is extremely rare on Earth. It is created in supernovae, but most Neptunium on Earth has already decayed.  

Neptunium doesn't have many uses out side of research and spacecraft.