Cassini’s New Breathtaking Image of Tethys

NASA’s Cassini spacecraft has sent back a breathtaking image of Tethys, a small, icy moon of Saturn.

Cassini’s narrow-angle camera took this image of Tethys on November 10, 2016. The view was acquired at a distance of approximately 228,000 miles (367,000 km) from Tethys. Image credit: NASA / JPL-Caltech / Space Science Institute.

At 662 miles (1,066 km) in diameter, Tethys is the fifth largest moon of Saturn.

It was discovered on March 21, 1684 by the Italian mathematician and astronomer Giovanni Domenico Cassini.

Tethys orbits 183,000 miles (295,000 km) from Saturn, taking 45.3 hours to circle the gas giant.

Tethys is tidally locked in phase with Saturn — the same side always faces toward the planet. The icy moon has gravitationally locked two smaller moons — Telesto and Calypso — into its own subsystem.

Also known as Saturn III, Tethys is a cold and heavily scarred body and is similar in nature to Saturn’s moons Rhea and Dione.

Tethys’ low mean density of 0.973 grams per cubic cm (0.97 times that of liquid water) implies that its interior is composed almost entirely of water ice plus a small amount of rock.

The icy moon has a high reflectivity (albedo) of 1.229 in the visual range, again suggesting a composition largely of water ice.

Tethys’ surface temperature is minus 305 degrees Fahrenheit (minus 187 degrees Celsius).

Like any solar system moon, Tethys has suffered many impacts.

These impacts are a prime shaper of the appearance of a moon’s surface, especially when the moon has no active geological processes.

In this case, a large impact not only created a crater known as Odysseus, but the rebound of the impact caused the mountainous peaks, named Scheria Montes, to form in the center of the crater.

The 280-mile-wide (450 km) Odysseus — named for a Greek warrior king in Homer’s two great works, The Iliad and The Odyssey — covers 18% of the moon’s surface area (a comparably sized crater on our planet would be as large as Africa).