Tethys

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Tethys' density is 0.97 times that of liquid water, which suggests that Tethys is composed almost entirely of water ice plus a small amount of rock. As with all but two of the major Saturnian moons, Tethys is tidally locked in phase with its parent -- one side always faces toward Saturn. It is a small moon 1,066 kilometers (662 miles) in diameter that orbits 294,660 kilometers (183,100 miles) from Saturn. This cold, airless, and heavily scarred body is very similar to sister moons Dione and Rhea except that Tethys is not as heavily cratered as the other two. This may be because its proximity to Saturn causes more tidal warming than on the other two moons, and that warming kept Tethys partially molten longer, erasing or dulling more of the early terrain. Tethys has a high reflectivity (or geometric albedo) of 1.229 in the visual range, again suggesting a composition largely of water ice, which would behave like rock in the Tethyan average temperature of -187 degrees Celsius (-305 degrees Fahrenheit).



Tethys Craters

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Tethys has two overpowering features, a giant impact crater and a great valley. Odysseus Crater dominates the Tethyan western hemisphere. Odysseus Crater is 400 kilometers in-diameter (almost 250 miles). That diameter is nearly two-fifths of Tethys itself

The second major feature, a valley called Ithaca Chasma (named for the country ruled by Odysseus), runs roughly from the Tethyan north pole to its south pole. It is 100 kilometers wide, 3 to 5 kilometers deep, and extends 2000 kilometers (62, 2 to3, and 1200 miles, respectively). Ithaca Chasma may have been caused by expansion of internal liquid water as it froze into ice after the surface had already frozen

                                Features of Tethys

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Tethys is definitely one of the most interesting worlds on out tour, but it does have a few notable surface features. In the western hemisphere can be seen a huge impact crater called Odysseus. At 248 miles (400 km) in diameter, this crater is nearly 2/5 the size of the entire moon. Astronomers are not quite sure why an impact of this size didn't shatter the moon completely. One theory suggests that Tethys may have been in a semi-liquid state at the time of the impact. Odysseus is a very flat crater that conforms to the shape of the moon itself, but it lacks the ringed mountains and central depression that characterize craters on Earth's moon or Mercury. The other major feature on Tethys is a huge valley called Ithaca Chasma. This canyon is about 60 miles (96 km) wide and 3 miles (4.8 km) deep, and runs 1,242 miles (2,000 km) long. It runs nearly 3/4 of the way around Tethys. These surface features suggest to astronomers that Tethys was not always frozen solid. Some believe that it may have existed in a liquid state at some time in the past. Tethys has several smaller impact craters, which are believed to have formed more recently. Tethys also contains no albedo features like the ones on Dione and Rhea.

                            Statistics for Tethys

Discovered by                            -    Giovanni Cassini
Year of Discovery                       -    1684
Diameter                                  -    662.4 miles (1,066 km)
Mean Distance from Saturn          -    182,714 miles (294,660 km)
Rotational Period                       -    1.89 Days
Orbital Period                            -    1.89 Days
Orbital Eccentricity                     -    0
Orbital Inclination                       -    1.09 degrees
Mean Surface Temperature          -    -305 F (-187 C)
Main Atmospheric Component       -    None
Apparent Magnitude                    -    10.2