Tethys (moon)

Giovanni Cassini

John F. Hershel

Map of Tethys PIA 14931 Jun 2012

Tethys size corrected

PIA19638-Tethys-SaturnMoon-TrailingHemisphere-Standard-20150411

PIA19638-Tethys-SaturnMoon-TrailingHemisphere-Enhanced-20150411

Tethys is a moon of Saturn, discovered by Giovanni Domenico Cassini in 1684. It is named after the Titan Tethys of Greek mythology. Tethys is notable for its high reflectivity, which is due to the water ice that constitutes the majority of its surface, making it one of the most reflective bodies in the Solar System. This moon has a number of distinctive features, including a massive canyon system named Ithaca Chasma and a large impact crater called Odysseus, which significantly influences its shape and geology.

Discovery and Naming

Tethys was discovered on March 21, 1684, by Giovanni Domenico Cassini, an Italian-French astronomer who also discovered three other moons of Saturn. The moon was named after the sea goddess Tethys from Greek mythology, who is the sister and wife of Oceanus, the god of the ocean. The naming convention of Saturn's moons typically follows the lineage of Titans, adhering to the mythological themes common in the naming of celestial bodies.

Physical Characteristics

Tethys is primarily composed of water ice, with a density so low that it is believed to be almost entirely made of ice with only a small amount of rock or other dense materials. This composition is consistent with the moon's very high albedo, or reflectivity, which allows it to reflect 80% of the sunlight that reaches its surface. Tethys has an irregular shape, with dimensions of approximately 1,060 by 1,060 by 1,060 kilometers, making it the sixteenth-largest moon in the Solar System.

Surface Features

The surface of Tethys is heavily cratered and cut by a number of large faults or valleys. The most prominent of these features is Ithaca Chasma, a huge valley that stretches about 2,000 kilometers long and 100 kilometers wide, covering approximately 75% of the moon's circumference. Another significant feature is the Odysseus crater, which is about 450 kilometers in diameter and is located in the western hemisphere of Tethys. The presence of these and other features suggests a history of intense geological activity, possibly driven by tidal forces from Saturn.

Orbit and Rotation

Tethys orbits Saturn at a distance of about 294,660 kilometers, taking approximately 1.9 Earth days to complete one orbit. Like many moons in the Solar System, Tethys is tidally locked to Saturn, meaning that one side of the moon constantly faces the planet. This tidal locking is a result of gravitational forces that have synchronized the moon's rotation period with its orbit period.

Exploration

Tethys has been observed by several spacecraft during flybys, including the Voyager missions in the early 1980s and the Cassini–Huygens mission, which arrived at Saturn in 2004. These missions have provided a wealth of information about Tethys, including detailed images of its surface, data on its composition, and insights into its geological history. However, no mission has yet landed on Tethys or studied it up close for an extended period.

Significance

The study of Tethys, like that of other moons of Saturn, provides valuable insights into the processes that shape the outer Solar System. Understanding the composition, geology, and orbital dynamics of Tethys helps scientists learn more about the formation and evolution of Saturn's moon system and the conditions in the early Solar System.