The Dutch-American astronomer Gerard Peter Kuiper (1905-1973). Kuiper studied at the University of Leiden, Holland, where he obtained his PhD in 1933. In the same year he emigrated to America where he worked in several universities and observatories. Kuiper's main research was on the solar system. He discovered two new satellites: Miranda, the fifth satellite of Uranus, in 1948 and Nereid, the second satellite of Neptune, in 1949. He proposed in 1951 that the short-period comets come from a flattened ring of comets, the Kuiper's belt, found beyond Neptune. He was involved in some of the early space missions including the Ranger and Mariner missions.