Nuclear fusion. Artwork showing some of the nuclei involved in nuclear fusion. This process liberates some of the immense amounts of energy stored in the nuclei of atoms, and is being studied on Earth as a potential source of power. The nuclei consist of protons (red) and neutrons (blue). At top are two nuclei, deuterium (upper left) and tritium (upper right), that can be fused to form lithium-5 (centre). This is highly unstable and decays to form helium-4 (lower left) and a neutron (lower right), resulting in an overall release of energy. A different form of fusion takes place in stars such as our Sun.