Moons of Saturn

by Fraser Cain on July 7, 2008

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Saturn and its moons. Image credit: NASA/JPL/SSI
Astronomers have discovered a total of 60 moons orbiting Saturn so far. Most of these moons are small, icy bodies; really just large chunks of the rings. But Saturn also has some of the largest, most dramatic moons in the Solar System. So far, 52 have been named.

Saturn’s largest moon, Titan was discovered by Christiaan Huygens in 1655, and then in the same century, Tethys, Dione, Rhea and Iapetus were discovered by Giovanni Cassini. Mimas and Enceladus were found in 1789 by William Herschel, and then Hyperion was discovered in 1848 by W.C. Bond, G.P. Bond and Lassell. All the rest of the moons were discovered by spacecraft and large Earth-based observatories in the last 20 years.

The closest large moon to Saturn is Mimas, which measures 397 km across, and orbits about 185,000 km above the center of Saturn. It’s best known for the huge crater, that makes it almost look like the Death Star from Star Wars. The impact that created this crater almost tore the moon apart.

The next large moon is Enceladus, measuring 504 km across, and orbiting at 238,000 km from the center of Saturn. NASA’s Cassini spacecraft recently discovered geysers of water ice pouring out of Enceladus’ southern pole. Astronomers think that there could be vast reserves of liquid water underneath the moon’s icy surface.

Next comes Tethys, measuring 1066 km across and orbiting at 295,000 km above the center of Saturn. Like many of Saturn’s moons, it’s composed almost entirely of water ice. You can see the cracks across Tethys’ surface from faults in the ice. The western hemisphere of Tethys is dominated by a huge impact crater called Odysseus, which is nearly 2/5ths the diameter of the moon itself.

And the next large moon is Dione, which measures 1123 km across and orbits at 377,000 km. Dione is also composed almost entirely of water ice, and the third densest of Saturn’s moons.

Next is Rhea, measuring 1529 km across and orbiting at 527,000 km – it’s Saturn’s second largest moon. It’s an icy body too, but it probably has 25% of its mass in rocks. It’s a bright world, with faint wispy marks across its surface. Astronomers think that Rhea might even have a tenuous ring system of its own.

Saturn’s largest moon is Titan, measuring 5151 km across. In fact, Titan is the second largest moon in the Solar System after Jupiter’s moon Ganymede. Titan is so important that the Cassini mission was carrying a special probe that dropped down onto the surface of Titan, capturing images during its descent. By analyzing the images from several flybys, scientists have discovered the presence of lakes and seas of liquid hydrocarbons scattered across the surface of Titan.

Two-toned Iapetus comes next, and it’s one of the strangest objects in the Solar System. It measures 1472 km across, and orbits at an altitude of 3.5 million km above Saturn. It has one hemisphere that’s white as snow, and the other side is black as coal. It also has a bizarre seam that runs along the moon’s equator, towering over the surrounding plains.

Here’s an article about the discovery of Saturn’s 60th moon, and another article about how Saturn’s moons could be creating new rings.

Want more information about Saturn’s moons? Check out NASA’s Cassini information on the moons of Saturn, and more from NASA’s Solar System Exploration site.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.

Reference:
NASA Solar System Exploration: Saturn’s Moons

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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