Plutonium was made in the laboratory by bombarding uranium with deuterons (an isotope of hydrogen consisting of a proton and a neutron), and named after the (then-) planet Pluto. So it is an artificial element, and there is likely no plutonium on Pluto. Uranium is the last of the natural elements (atomic number 92) in the periodic table. When the historic Iran Nuclear Deal was announced this week, uranium and plutonium was in the news. Here is the New York Times’s simple guide to the terms of the deal.