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Moon Descriptions

Moon Descriptions


Mimas [MY-mass] is one of the innermost moons of Saturn. William Herschel discovered the moon in 1789, and one of the moon's most distinct features is one super crater, named after him. The crater is so big that it takes up nearly 1/3 the diameter of the whole moon, with a peak in its center nearly 2/3 as high as Mount Everest. The impact that formed Mimas may have caused the fractures seen on the moons opposite side. Mimas' density and appearance suggest that it is a sphere of water ice with small pieces of rock mixed into the surface. Its gravity causes the Cassini division, the large gap between Saturn's A and B rings, and its force is just strong enough to pull it into a spherical shape, but weak enough to permit large surface features.

Mass: 3.81x1019 kg
Density: 1.17 g/cm3
Diameter: 396 km / 246 miles
Distance from Saturn: 185,520 km / 115,280 miles


Enceladus [en-SELL-ah-dus] is one of the innermost moons of Saturn. It is quite similar in size to Mimas but has a smoother, brighter surface. Enceladus reflects almost 100 percent of the sunlight that strikes it and is one of the coldest objects in the Solar System. Temperatures often only reach about -201°C (-330°F), but through a combination of tidal flexing and radioactive material, its interior is thought to be warm enough to liquefy water. Unlike Mimas, Enceladus displays at least five different types of terrain. Parts of Enceladus show craters no larger than 35 km in diameter. With Cassini's imaging of sprouting geysers in 2005, suggesting subsurface pools of liquid water, Enceladus joined the handful of solar system bodies suspected of being capable of supporting life. The geysers eject icy particles and water vapor from the moon's South Pole region, which gives the small moon an atmosphere. This material also feeds Saturn's E-ring; the broad outermost ring in which Enceladus is embedded.

Mass: 1.2x1020 kg
Density: 1.24 g/cm3
Diameter: 504 km / 313 miles
Distance from Saturn: 237,378 km /147,500 miles


Dione [dy-OH-nee] was discovered in 1684 by Giovanni Cassini. It is an icy body similar to Tethys and Rhea. Its density is 1.43 gm/cm3, which makes it the densest moon of Saturn other than Titan. Dione is probably composed of a rocky core making up one-third of the moon's mass, with the rest consisting of water ice. Dione's icy surface includes heavily cratered terrain, moderately cratered plains and lightly cratered plains. The heavily cratered terrain has craters greater than 100 kilometers in diameter. However, the plains area tends to contain craters that are less than 30 kilometers in diameter. Much of the heavily cratered terrain is located on the trailing hemisphere, with the less cratered plains area existing on the leading hemisphere. This is opposite from what some scientists expected.

Mass: 1.10x1021 kg
Density: 1.43 g/cm3
Diameter: 1,123 km / 698 miles
Distance from Saturn: 337,400 km / 209,650 miles


Tethys [TEE-thiss] was discovered by Giovanni Cassini in 1684. Density measurements indicate that Tethys [TEE-thiss] is almost entirely made up of pure water ice. Two features dominate its surface: a giant crater called Odysseus, blasted by an impact that could have shattered a once smooth surface, and a chasm called Ithaca Chasma that stretches three-quarters of the way around the circumference - far longer, wider, and deeper than Earth's Grand Canyon. Both of these distinct features probably formed when Tethys' interior had not yet become frozen solid. As liquid froze and expanded, it likely cracked its shell, forming the chasm. Tethys shares its orbit with two smaller moons. Telesto leads the way and Calypso brings up the rear as the three satellites circle Saturn.

Mass: 6.17x1020 kg
Density: 1.21 g/cm3
Diameter: 1,066 km / 662 miles
Distance from Saturn: 294,660 km / 183,090 miles


Rhea [REE-uh] is the second largest satellite of Saturn, and was discovered in 1672 by Giovanni Cassini. It is made up of mostly water ice, with a rocky core providing less than a third of its mass. Its highly reflective surface contains some dark material which may be tholins, the type of organic substance found in Titan's atmosphere. Like Dione, Rhea has bright wispy markings on its trailing hemisphere, thought to be fractures in the surface. It is among the most heavily cratered of Saturn's moons but, unlike Dione, its leading face has more craters than its trailing face.

Mass: 2.31x1021 kg
Density: 1.33 g/cm3
Diameter: 1529 km / 950 miles
Distance from Saturn: 527,040 km / 327,490 miles


Discovered in 1655 by the Dutch astronomer Christiaan Huygens, Titan is the biggest of the 52 known moons orbiting Saturn. It is a cold world enclosed by a thick, hazy atmosphere. With an equatorial radius of 2,575 kilometers (1,600 miles), Titan is the second largest moon in our solar system. It's bigger than Earth's moon and even the planet Mercury. Because of the extremely cold temperatures typical of celestial bodies that are that far away from the Sun, the structure of Titan's chemical atmosphere is in a state of deep freeze. It is this chemical composition that interests scientists a great deal because Titan's atmosphere might consist of compounds similar to those present in the primordial days of the Earth's atmosphere. ESA's Huygens probe rode with Cassini to the Saturnian system, then parachuted to a soft landing on Titan in January, 2005.

Mass: 1.34x1023 kg
Density: 1.88 g/cm3
Diameter: 5,150 km / 3,200 miles
Distance from Saturn: 1,221,850 km / 759,222 miles


Iapetus [eye-AP-eh-tuss] Two-faced Iapetus (eye-AP-eh-tuss) is one of Saturn's strangest moons. Half of it is as dark as asphalt, while the other half is as bright as snow. The dark half faces forward as Iapetus moves in its nearly circular, inclined orbit around Saturn. Scientists generally believe that it has swept up the orbiting dark material (perhaps originally from Phoebe) that covers its forward-facing surface. The light side is about ten times brighter than the dark side. Also, a huge mountain ridge stretches roughly a third or more of the way around its equator, with peaks substantially higher than Mt. Everest. Scientists are uncertain about the cause of either phenomenon. Iapetus orbits Saturn well outside of the rings, in an orbit inclined 15 degrees away from the ring plane. Its flattened shape suggests that it once rotated faster than it does now.

Mass: 1.6x1021
Density: 1,21 g/cm3
Diameter: 1,471 km / 914 miles
Distance form Saturn: 3,561,300 km / 2,212,890 miles

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