Hyperion

Hyperion is one of Saturn’s moons. It was discovered in 1848 by the American astronomer William Cranch Bond, his son George Phillips Bond and British astronomer William Lassell.

Hyperion is the 8th largest of Saturn’s moons and the largest irregular-shaped object in the Solar System. Saturn has 62 moons with confirmed orbits, 53 of which have names. 24 of these are regular satellites that orbit Saturn with only small inclinations to the planet’s equatorial plane. 37 of the remaining 38 are irregular satellites that orbit at high inclinations and a much greater distance from Saturn. These are probably minor planets that have been captured by the planet’s gravity or they could also be debris from these planets as they were captured. The final irregular satellite is unclear.

Saturn was the Roman god of agriculture and harvest and its moons were at first named after the brothers (Titans) and sisters (Titanesses) of the god. When these names were exhausted, other names were taken from additional characters in Greek or Roman mythology or figures from the mythology of other cultures. The irregular satellites were given names from figures from Inuit, Gallic and Norse mythology. Hyperion was a Titan and the god of watchfulness in Greek mythology. The name was first suggested 1847 by British astronomer John Herschel, the son of William Herschel. Titan is also designated Saturn VI as the fifth moon going outward from the planet.

Hyperion’s composition is mainly water-ice with some rock and it resembles a pile of rubble. It has a density about half that of water. The moon’s porosity is estimated at 0.46, meaning that 46% of its volume is empty space. Unlike other Saturn moons, it does not reflect light easily and appears to be covered with thin dark material. Hyperion’s surface is spotted with thin, sharp-edged craters that make the moon look like a sponge. A reddish substance whose composition includes carbon and hydrogen has accumulated at the bottom of the craters.

In contrast to most of Saturn’s moons, Hyperion is not locked tidally into an orbit with Saturn and does not have a stable rotation around its own axis. It can change its own rotation over a period as short as a month and follow this with thousands of years of regular rotation. Hyperion takes 21.27 Earth days to orbit Saturn. Along with Saturn and its other satellites, it takes 29.4 Earth years to orbit the sun.

The closest spacecraft approach to Hyperion has been with the Cassini mission flyby in 2005 that came within 500 km of the moon. Later flybys in 2011 passed Hyperion at 58,000 km.