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Orbit: 294,660 km from Saturn
Orbital period: 45 hours
Gravity: 0.145 m/s²
Circumference: 3,349 km
Diameter: 1060 km
Mass: 6.22e20 kg


Tethys or Saturn III is a mid-sized moon of Saturn about 1,060 km across. It was discovered by G. D. Cassini in 1684 and is named after titan Tethys of Greek mythology.

Tethys’ low density indicates that it is almost completely composed of  water ice, similar to Dione and    Rhea.

Saturn's moon Tethys

The western hemisphere is dominated by a huge impact crater,  called Odysseus, whose 400 km  diameter is  nearly 2/5 of that of Tethys itself  (right). That such an impact        didn’t shatter Tethys completely indicates that it may have been liquid  or  at least not very solid at the time. The crater is now quite flat (or  more  precisely, it conforms to Tethys’ spherical shape),  like the craters on Callisto, without  the high ring mountains and  central peaks commonly seen on the Moon and   Mercury.

The second major feature seen on Tethys is a huge valley (called Ithaca Chasma) 100 km wide and 3 to 5 km deep which runs 2000 km or  3/4 of  the way around Tethys’ circumference.

Clearly then, Tethys has not always been frozen solid. At some point in its       past it was probably liquid. The impact craters from that era have been  smoothed out.  As it froze and expanded, the surface must have  cracked to  accommodate the extra volume producing Ithaca Chasma. The smaller  impact  craters we see today are more recent.

There are no albedo feature on  Tethys as there are on  Rhea and Dione.

Telesto and Calypso orbit in Tethys’  Lagrange points  (60 degrees ahead and behind Tethys in the same orbit).


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