  deuterium (symbol  or , also known as heavy hydrogen) is one of two stable isotopes of hydrogen. the nucleus of deuterium, called a deuteron, contains one proton and one neutron, whereas the far more common hydrogen isotope, protium, has no neutron in the nucleus. it has a natural abundance in earth's oceans of about one atom in  of hydrogen. thus deuterium accounts for approximately 0.0156% (or on a mass basis: 0.0312%) of all the naturally occurring hydrogen in the oceans, while the most common isotope (hydrogen-1 or protium) accounts for more than 99.98%. the abundance of deuterium changes slightly from one kind of natural water to another (see vienna standard mean ocean water). the deuterium isotope's name is formed from the greek deuteros meaning "second", to denote the two particles composing the nucleus. deuterium was discovered and named in 1931 by harold urey, earning him a nobel prize in 1934. this followed the discovery of the neutron in 1932, which made the nuclear structure of deuterium obvious. soon after deuterium's discovery, urey and others produced samples of "heavy water" in which the deuterium has been highly concentrated with respect to the protium. because deuterium is destroyed in the interiors of stars faster than it is produced, and because other natural processes are thought to produce only an insignificant amount of deuterium, it is thought that nearly all deuterium found in nature was produced in the big bang 13.8 billion years ago, and that the basic or primordial ratio of hydrogen-1 (protium) to deuterium (about 26 atoms of deuterium per million hydrogen atoms) has its origin from that time. this is the ratio found in the gas giant planets, such as jupiter. however, different astronomical bodies are found to have different ratios of deuterium to hydrogen-1, and this is thought to be as a result of natural isotope separation processes that occur from solar heating of ices in comets. like the water-cycle in earth's weather, such heating processes may enrich deuterium with respect to protium. in fact, the discovery of deuterium/protium ratios in a number of comets very similar to the mean ratio in earth's oceans (156 atoms of deuterium per million hydrogens) has led to theories that much of earth's ocean water has a cometary origin.{{cite journal|doi=10.1038/nature10519|journal=nature|volume= 478|pages=218â220|year=2011|title=ocean-like water in the jupiter-family comet 103p/ha
Environmental_isotopes Isotopes_of_hydrogen Neutron_moderators Nuclear_fusion_fuels Nuclear_materials