Tethys

Tethys is a mid-sized, icy moon of Saturn. It was discovered in 1684 by Giovanni Domenico Cassini and is named after Tethys, the Ocean Titaness in Greek mythology. Tethys orbits Saturn at an average distance of about 295,000 kilometers and completes an orbit in roughly 1.89 days. The moon is tidally locked to Saturn, showing the same face to the planet at all times.

Tethys measures about 1,060 kilometers in diameter and is composed primarily of water ice with a smaller rocky component. Its surface is relatively bright, indicating a youthful exposure of ice, though heavily cratered in places. The most prominent surface feature is Ithaca Chasma, a massive trough system extending for roughly 1,500–2,000 kilometers across the moon. The large crater Odysseus, about a few hundred kilometers in diameter, presides on its surface as well.

Tethys is believed to be differentiated, with an icy crust and possibly an iron-poor rocky interior, and it likely formed in Saturn’s sub-nebula, later migrating to its current orbit. It has been studied extensively by the Cassini–Huygens mission, which provided high-resolution imaging and gravity data, helping to map its geology and its interaction with Saturn’s magnetosphere and the E ring. The name and designation are governed by the International Astronomical Union.