| Proper Name | Hyperion | | Designation | Saturn VII | | Primary Planet | Saturn | | Orbital Period | 21 days, 6 hours, 38 minutes | | Distance from Saturn | Semi-Major Axis: 1,481,010 km
Periapsis: 1,298,837 km
Apoapsis: 1,663,183 km | | Eccentricity | 0.1230 | | Rotation Period | Variable (chaotic) | | Mean Diameter | 270 km
168 miles | | Notes | Hyperion is unusual for a moon of its size in having an irregular, elongated shape. Also highly unusual is the fact that it does not rotate on a fixed axis, but instead tumbles chaotically as it circles the planet Saturn. |
Hyperion is an elongated and irregular moon, indeed one of the largest irregular moons known. It orbits Saturn at a distance varying around 1.5 million kilometres, beyond the orbit of the gigantic moon Titan. Hyperion itself is named for one of the titans: Hyperion was the brother of Cronos (Cronos being the Greek name for Saturn). While Titan has a diameter exceeding 5,0000 km, Hyperion is little more than a splinter by comparison, measuring just 360 km along its longest axis.
The larger and much more massive inner moon has affected Hyperion's orbit, which follows a resonant pattern with the orbit of Titan. Unlike most - in fact almost all - other moons, Hyperion does not rotate periodically on its axis. Instead it tumbles chaotically and unpredictably, probably at least partly due to the influence of its massive neighbour Titan.
Hyperion is mainly composed of water ice and accumulated rubble, within which the moon contains a significant amount of empty space. The surface is covered by drifts of material deposited by outer moons, either its outer neighbour Iapetus or the more distant Phoebe. This structure goes some way to explaining the moon's unusual cratering: Hyperion is peppered by small, narrow craters with dark floors, giving the moon a distinctive, rather sponge-like appearance.
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