Tethys (moon)

Tethys is a moon of Saturn that was discovered by Giovanni Cassini in 1684.

Name

Tethys is named after the titan Tethys of Greek mythology. It is also designated Saturn III or S III Tethys.

Cassini named the four moons he discovered in 1671–1684 (Tethys, Dione, Rhea and Iapetus) Sidera Lodoicea ("the stars of Louis") to honor king Louis XIV.

The correct adjectival form of the moon's name is Tethyan, although other forms are also used.

Physical characteristics

Tethys is an icy body similar in nature to the moons Dione and Rhea. The density of Tethys is 0.97 g/cm³, indicating that it is composed almost entirely of water-ice. The Tethyan surface is heavily cratered and contains numerous cracks caused by faults in the ice. Its surface is one of the most reflective (at visual wavelengths) in the solar system.

There are two different types of terrain found on Tethys, one composed of densely cratered regions and the other consisting of a dark colored and lightly cratered belt that extends across the moon. The light cratering of this second region indicates that Tethys was once internally active, causing parts of the older terrain to be resurfaced. The exact cause of the darkness of the belt is unknown.

The western hemisphere of Tethys is dominated by a huge impact crater called Odysseus, whose 400 km diameter is nearly 2/5 of that of Tethys itself.

The second major feature seen on Tethys is a huge valley called ‘’Ithaca Chasma’’, 100 km wide and 3 to 5 km deep. It runs 2000 km long, approximately 3/4 of the way around Tethys' circumference. It is thought that Ithaca Chasma formed as Tethys' internal liquid water solidified, causing the moon to expand and cracking the surface to accommodate the extra volume within.

Flybys

The Cassini orbiter performed a close targeted flyby of Tethys on September 23, 2005 at the distance 1500 km. Although Cassini will continue to observe Tethys at moderate distances during its extended mission, there are no plans for further close fly-bys.