Other Notable Saturnian Moons
The other four largest moons of Saturn are Tethys, Dione, Rhea, and Iapetus.
Tethys is 650 mi (1,060 km) in diameter. Its surface is heavily cratered, and it has a huge, globe-girdling canyon, Ithaca Chasma. Part of the canyon stretches over three-quarters of the satellite's surface. Ithaca Chasma is about 1,550 mi (2,500 km) long. It has an average width of about 62 mi (100 km) and a depth of 1.8 to 3.1 mi (3 to 5 km).
Tethys also has a huge impact crater named Odysseus that is 244 mi (4,400 km) in diameter, or more than one-third of the moon's diameter.
Dione is slightly larger than Tethys, 696 mi (1,120 km) in diameter, and is more than half composed of water ice. It has bright, wispy markings resembling thin veils covering its features.
Rhea, the largest of the inner satellites, is 951 mi (1,530 km) in diameter. It is composed mainly of water ice, causing its reflective surface to present an almost uniform white appearance.
Iapetus is the outermost of Saturn's icy satellites. Its appearance is unique because it has one dark and one bright hemisphere. The origin of the black coating of its dark face is unknown. Iapetus has a diameter of 907 mi (1,460 km).
Other notable moons of Saturn are Mimas, Enceladus, Hyperion, Phoebe, and Pan.
Mimas is small, only 244 mi (329 km) in diameter. It has a huge impact crater, Herschel, nearly one-third of its diameter. The crater is about 81 mi (130 km) wide and its icy peak rises almost 6.2 mi (10 km) above the floor. Mimas is believed to be composed mainly of water and ice and to contain between 20% and 50% rock.
Enceladus is remarkable in that its surface shows signs of extensive and recent geological activity. There may be active water volcanism. The surface is extremely bright, reflecting more than 90% of incident sunlight. This suggests that its surface is composed of extremely pure ice without dust or rocks to contaminate it. Enceladus has a diameter of 310 mi (500 km). The Cassini spacecraft observed icy geysers at the moon's south pole, exciting scientists with the presence of liquid water and suggesting that the satellite rolled over and produced this warm spot at what would usually be a cold polar region.
Hyperion orbits between Iapetus and Titan. It is irregular in shape, measuring about 248 by 155 by 124 mi (400 by 250 by 200 km). It may be a remnant of a much larger object that was shattered by impact with another space body. It appears that Hyperion is composed primarily of water ice.
Hyperion orbits Saturn with an irregular motion (“chaotic tumbling”).
Phoebe travels in a retrograde orbit at a distance of over 6.2 million miles (10 million kilometers) away from the planet. It is the darkest moon of Saturn and is the planet's only known satellite that does not keep the same face always turned to Saturn. It has been speculated that it is an asteroid that was captured by the planet. Phoebe rotates in about nine hours and orbits Saturn in 406 days. It has a diameter of 124 mi (200 km).
Pan was discovered in 1990 from Voyager 2 photos taken in 1981. The satellite is estimated to be about 12.43 mi (20 km) in diameter, and it orbits within the Encke Gap, a 202-mile (325-kilometer) division in Saturn's A ring. It was identified by Johann Franz Encke (1791–1865) in 1837.
Twenty-eight more moons of Saturn have been discovered since 2000, including 12 found in Dec. 2004 using Hawaii’s Mauna Kea telescope. These 28 satellites range in size from 1.8 to 30 mi (3 to 48 km) in diameter.
Saturn is the last of the planets visible to the naked eye. Saturn is never an object of overwhelming brilliance, but it looks like a bright star. The rings can be seen with a small telescope.
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