Object Analysis

Tethys is a mid-sized moon of Saturn discovered by Giovanni Domenico Cassini in 1684. It is composed almost entirely of water ice, with only a tiny fraction of rock. This makes it one of the most "pure" icy bodies in the Solar System. Its surface is highly reflective and appears bright white.

Two massive features dominate Tethys. The first is Odysseus, a giant impact crater 400 km wide—two-fifths the diameter of the moon itself. Despite its size, the crater is quite flat, as the icy crust has "relaxed" over billions of years. The second is Ithaca Chasma, a gargantuan canyon system that stretches three-quarters of the way around the moon.

Ithaca Chasma is likely the result of the moon expanding as its internal liquid water froze into ice billions of years ago. Tethys is also home to a mysterious "red arc"—faint, reddish streaks on its surface whose origin is still unknown. Like Dione, it has two trojan moons, Telesto and Calypso, that share its orbit.