Hyperion (moon)

Hyperion (hye-peer'-ee-un, Greek ????????) is a moon of Saturn discovered by William Cranch Bond, George Phillips Bond and William Lassell in 1848. It is distinguished by its irregular shape, its chaotic rotation, and its unexplained sponge-like appearance.

Physical characteristics

Shape

Hyperion is the largest highly irregular (non-spherical) body in the solar system. (Proteus is quite a bit larger but is almost spherical.)

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The most likely explanation for this is that Hyperion is a fragment of a larger body that was broken by a large impact in the distant past.

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The largest crater on Hyperion is approximately 120 km in diameter and 10 km deep.

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Composition

Like most of Saturn's moons, Hyperion's low density indicates that it is composed largely of water ice with only a small amount of rock. It is thought that Hyperion may be similar to a loosely accreted pile of rubble in its physical composition. However, unlike most of Saturn's moons, Hyperion has a low albedo (0.2–0.3), indicating that it is covered by at least a thin layer of dark material. This may be material from Phoebe (which is much darker) that got past Iapetus. Hyperion is redder than Phoebe and closely matches the color of the dark material on Iapetus.

Related Topics:
Phoebe - Iapetus - Red

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Surface features

Voyager 2 passed through the Saturn system but photographed Hyperion only from a distance. It discerned individual craters and an enormous ridge but was not able to make out the texture of the moon's surface. Early images from the Cassini orbiter suggested an unusual appearance, but it was not until Cassinis sole targeted flyby of Hyperion on September 25, 2005 that the moon's oddness was revealed in full.

Related Topics:
Voyager 2 - Cassini - September 25 - 2005

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Hyperion is entirely saturated with deep, sharp-edged craters that give it the appearance of a giant sponge. Dark material fills the bottom of each crater. Nothing has yet been published to explain these features.

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See also: List of geological features on Hyperion

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