Hyperion, named after a Titan god and also known as Saturn VII, is a moon (natural satellite) of Saturn which was discovered on 16 Sep 1848, by William Bond, George Bond, and William Lassell. The dimensions of Hyperion are 360.2 km × 266.0 km and the mass is (5.6199±0.05)x1018 kg.
Hyperion is highly irregular in shape and is filled with deep, sharp-edged craters which gives it a sponge-like appearance. Neptune's moon Proteus is the largest irregular shaped moon in our solar system. Hyperion's largest crater is approximately 121.57 km in diameter and 10.2 km deep. A possible explanation for the non-ellipsoidal shape is that the moon is a fragment of a larger celestial body that was broken up by an impact in the distant past.
Hyperion is quite porous with a porosity of about 0.46 and its low density shows that it is largely composed of water ice with only a small fraction of rock. The odd shape of the moon was revealed in full by the Cassini orbiter. The surface is covered with craters and the bottom is filled with dark material. Hyperion has a weak surface gravity. The characteristics of the moon show that impactors compress its surface rather than digging it, and any material that leaves the surface never returns.
Images from the Voyager 2 (space probe launched by NASA) and ground-based photometry shows that Hyperion's axis of rotation wobbles so much that its orientation in space cannot be predicted. On 26 Sep 2005, Cassini orbiter came closest to Hyperion, the first closest targeted flyby occurred at a distance of 500 km. Later on, Cassini made two more flybys at distances of 58,000 km and 34,000 km in 2011 and 2015.
Source: Wikipedia
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