1948

Miranda

Gerard P. Kuiper (1905–1973)

The rate of discovery of large (hundreds of miles in size) planetary moons dropped precipitously after the discovery of Saturn’s moon Phoebe in 1898. After several decades with no major new moons discovered, solar system studies went out of fashion, probably because many early-twentieth-century astronomers probably thought that the census of the solar system’s main bodies was relatively complete.

One scientist who continued to study and observe the planets, however, was the Dutch-American astronomer Gerard P. Kuiper. Starting in the late 1930s, Kuiper worked at the University of Chicago’s Yerkes Observatory (home of the largest refracting telescope in the world) and the new McDonald Observatory in Texas, which had a telescope with the resolution and sensitivity that Kuiper needed to search for faint new planetary satellites. In 1948 he discovered the fifth, and innermost, satellite of Uranus. Following the established theme, he named the new moon Miranda, after a character from Shakespeare’s The Tempest.

Little was known about Miranda besides its orbit, small size, and likely icy composition until the Voyager 2 flyby of the Uranus system in 1986. Miranda is indeed small, with a relatively spherical shape about 292 miles (470 kilometers) in diameter. But its surface is surprisingly diverse, consisting of a patchwork of regions covered by bright and dark ridges and cliffs interspersed with bland, heavily cratered, icy terrain. It looks like Miranda was taken apart and then put back together, clumsily. Some astronomers think an ancient impact may have done just that.

Whole-disk Voyager 2 view of the jumbled surface of Miranda.

In 1949 Kuiper also discovered a second moon of Neptune, which he named Nereid. He was a founding father of modern planetary science, pioneering the use of spectroscopy to study planets and moons. Kuiper discovered carbon dioxide in the atmosphere of Mars, a methane atmosphere around Saturn’s moon Titan, and helped pick the Apollo lunar landing sites in the 1960s.

High-resolution mosaic of part of the icy surface of Miranda, photographed during the Voyager 2 flyby of Uranus in 1986. The incredibly sheer cliff at the lower right is possibly more than 66,000 feet (20 kilometers) high.