Plutonium completes the planetary trio that runs uranium, neptunium, plutonium, taking its name from Pluto, which had been discovered only in 1930 and named for the Roman god of the underworld and the dead, the ruler of the realm of shades and, in another aspect, the giver of the buried wealth of the earth. The name proved grimly apposite, for plutonium became the fissile core of the bomb dropped on Nagasaki in 1945 and a central material of the nuclear arms race, an element of the underworld indeed.
Seaborg is said to have chosen the symbol Pu, rather than the more logical Pl, half in jest. The naming is astronomical in form, but through the god of the dead it gives this weapon-material one of the darkest and most fitting associations in the periodic table. Popular imagination often exaggerates plutonium's danger in one particular way: its alpha radiation cannot penetrate skin or even a sheet of paper, so a sealed sample can be handled with gloves relatively safely, and the real hazard comes from inhaling or ingesting even microscopic particles, which then irradiate internal tissue directly, a distinction lost in most dramatic popular depictions of the metal as something instantly lethal to the touch.