Neutrinos are sometimes called ghost particles because they are difficult to trap, or locate. If your thumb is perpendicular to the sun, then about 65 billion neutrinos are going through your thumb each second. Neutrinos are produced in the heart of the sun, in supernova explosions, in nuclear reactions, and in a few other ways. Neutrinos are almost massless, they carry 1/2 integer spin, and they interact only through the weak force and gravity. It was long of matter of debate for physicists whether neutrinos even had mass, but Canadian physicist Dr. Art MacDonald of the Sudbury Neutrino Observatory received a Nobel prize in physics in 2015 for proving that neutrinos do have mass. Since neutrinos can oscillate between different flavors, or kinds, that was the necessary item needed to prove they have mass. Neutrino physics took off in 1987 when neutrinos from Supernova SN1987A were detected on Earth, just before the light from the SN reached us.