who discovered Miranda and Nereid, was a member of the team which discovered Janus, and who made many important studies of planetary and lunar features and the origin of the solar system. He also predicted, in 1948, that carbon dioxide is one of the major constituents of the martian atmosphere and discovered that Titan has a methane atmosphere. He suggested that material left over from the formation of the solar system might form a belt, now called the Kuiper belt, beyond the orbit of Pluto. Kuiper was born at Harenskarspel and educated at Leiden. He migrated to the USA in 1933 and became a US citizen in 1937. He worked at the Yerkes Observatory, University of Chicago, and was its director from 1947 to 1949 and again from 1957 to 1960. From 1960 until his death he was director of the Lunar and Planetary Laboratory, University of Arizona. The International Astronomical Union named a crater and geologic period on Mercury for him.