Saturn - Moons 2

MIMAS:

Mimas is the seventh moon of Saturn. It has an orbit of 185,520 km from Saturn and a diameter of 392 km. The mass of this moon is 3.80e19 kg. This satellite was discovered by Herschel in 1789. It has a very low density, 1.17, showing that it is mostly water ice and some amount of rock. Mimas' surface is dominated by an impact crater that is actually 130 km across. This crater is called Herschel, and is 1/3 of the diameter of the entire moon. It's walls are 5 km high, and its floor is about 10 km deep, and its central peak rises 6 km above the crater floor. The cause of this crater must have severely disrupted Mimas, there are even fractures on the opposite side of Mimas that may be due to the same reason. The surface of Mimas is covered with impact craters. The size of Herschel suggests that Mimas was impacted by even larger bodies than the one that created Herschel which completely disrupted the new moon and also in turn, wiping out the evidence of earlier large impacts. The impact debris fused together again to form what we know as Mimas.

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ENCELADUS:
Courtesy of NASA/NSSDC. Enceladus is the eighth satellite of Saturn. It has an orbit of 238,020 km from Saturn and a diameter of 498 km. The mass is 7.30e19 kg. This moon was discovered in 1789 by Herschel. Enceladus has the highest albedo, greater than .9, than any body of matter in the solar system. The surface is made of clean ice, but its terrain has five different types (at least). Enceladus has, in addition to craters, smooth plains and extensive linear cracks and ridges. Some of the surface is relatively new, and probably formed less than 100 million years ago. This means that Enceladus must have been active until recently, maybe by water volcanism. Enceladus is very small and can not be heated by radioactive decay in the interior. Enceladus is locked in a 1:2 resonance with Dione. This may have provided a heat mechanism but not sufficient enough to melt the water ice. Therefore, Enceladus may be made up of a low-melting point material rather than just pure water. It may be the source of the material in Saturn's E ring.

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TETHYS:
Courtesy of NASA/NSSDC. Tethys is the ninth satellite. It has an orbit of 294,660 km from Saturn and a diameter of 1060 km. The mass is 6.22e20 kg. It was discovered by Cassini in 1684. Tethys' low density indicates that it is almost completely composed of water ice. The western hemisphere has a large impact crater, called Odysseus. It is 400 km in diameter, and nearly 2/5 of Tethys. Since the impact didn't shatter Tethys, it indicates that it may have not very solid at the time. The crater is flat now, or conforms to Tethys' spherical shape. A second major feature on Tethys is a huge valley, called Ithaca Chasma. It is 100 km wide and 3 to 5 km deep. It runs about 2000 km or 3/4 of the way around Tethys' circumference. This shows that Tethys has not always been frozen solid. At some point, it was liquid. The impact craters have been smoothed out. As it froze and expanded, the surface may have cracked to accommodate for the extra volume producing Ithaca Chasma. The smaller impact craters we see today are more recent. Telesto and Calypso in Tethys' Lagrange points, meaning that they are 60 degrees ahead and behind Tethys in the same orbit.

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TELESTO:
Telesto is the tenth satellite of Saturn. Its orbit is 294,660 km from Saturn and it has a diameter of 29 km. The mass is unknown. This moon was discovered in 1980 by Smith, Reitsema, Larson and Fountain from ground-based observations. Telesto is in Tethys' leading Lagrange point.

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CALYPSO:
Calypso is the eleventh of Saturn's known satellites. It has an orbit of 294,660 km from Saturn and a diameter of 26 km. The mass is unknown. This satellite was discovered by Pascu, Seidelmann, Baum and Currie in 1980 from ground-based observations with prototype cameras destined for the HST. Calypso is in Tethys' trailing Lagrange point. Calypso and Telesto are among the smallest moons in the entire solar system.

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