When the Nobel Foundation awarded Ray Davis and Masatoshi Koshiba the 2002 Nobel Prize in Physics, it could have chosen to emphasize any of their many accomplishments. Davis made his name detecting neutrinos from the sun—the first of these notoriously elusive particles ever seen from beyond our planet—and Koshiba discovered them coming from the great supernova explosion of 1987. Their work was an experimental tour de force and helped to establish that neutrinos, which theorists had assumed were massless, in fact have a small mass. Yet the Nobel Foundation recognized Davis and Koshiba, above all, for establishing a new branch of science: neutrino astronomy.