Nuclear fusion is a reaction in which two atoms collide and combine to create a new atom. In the core of the sun, it is thought that hydrogen atoms cause nuclear fusion, transforming into helium atoms. Because the earth contains abundant hydrogen, discovering how to control nuclear fusion could lead to the creation of artificial suns as the ultimate energy source. The most easily accomplished fusion is between deuterium and tritium (two forms of heavy hydrogen), but even this is not at all simple, since sparking such a reaction requires a temperature of almost 100 million degrees. The use of lasers to trigger fusion events is one of methods currently being studied.