Neutrino
. Neutrino, very small particles with no electric charge and little or no mass. Neutrinos are elementary particles —that is, they cannot be broken into smaller particles. Neutrinos are so small that they pass right through most material. One important kind of neutrino is created in the nuclear reactions that give the Sun its energy. The Sun produces so many neutrinos that 70 billion neutrinos pass through every square centimeter (0.15 sq in) of the surface of Earth every second. Scientists study neutrinos to learn more about the reactions that give the Sun its energy. Similar reactions occur in radioactive substances, or materials made up of atoms that spontaneously change into other particles ( Radioactivity ). Neutrinos also help scientists understand these radioactive reactions. Neutrinos play an important part in the theory scientists have developed to explain the elementary particles that make up all matter and energy. Neutrinos have so little mass that scientists are not sure tha