Very little is known about the neutrino, even whether it has mass; it appears to be like the photon, i.e. mass less and traveling at the speed of light, though it is quite possible that it does have a very small, as yet unmeasured mass.
One explanation for the solar neutrino problem put forward is that the neutrino, once created at the sun’s core, decays into another particle that cannot be detected by present experiments on its way to earth. But if the neutrino travels at the speed of light, it takes not more than about eight minutes to reach earth, and so the decay must occur in this time. This idea has now ceased to be acceptable since neutrinos were detected from the 1987 supernova in the Large Magellanic Cloud, and they must have been traveling for thousands of years .
