NASA’s Cassini spacecraft has returned a spectacular new image of Tethys, a small, icy moon of Saturn.
This view of Tethys was taken by NASA’s Cassini spacecraft on April 11, 2015. The crater Odysseus is seen at the right of the image. Image credit: NASA / JPL-Caltech / Space Science Institute.
Discovered on 21 March 1684 by the Italian mathematician and astronomer Giovanni Domenico Cassini, Tethys is a cold and heavily scarred body, about 662 miles (1,066 km) in diameter.
Saturn’s fifth largest moon, also known as Saturn III, is similar in nature to sister moons Rhea and Dione except that Tethys is not as heavily cratered as the other two.
Tethys has two impressive features: a huge crater and a great canyon.
The 280-mile-wide (450 km) impact crater Odysseus – named for a Greek warrior king in Homer’s two great works, The Iliad and The Odyssey – dominates the western hemisphere of Tethys, covering 18% of the moon’s surface area. A comparably sized crater on our planet would be as large as Africa.
The second feature is a long canyon called Ithaca Chasma – named for the country ruled by Odysseus. It is around 60 miles (100 km) wide, 2-3 miles (3-5 km) deep, and extends 1,200 miles (2,000 km). Some planetary scientists suggest the canyon may have been caused by expansion of internal liquid water as it froze into ice after the surface had already frozen.
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).
Tethys has been approached by several spacecraft including Pioneer 11 in 1979, Voyager 1 one year later, Voyager 2 in 1981, and multiple times by NASA’s Cassini spacecraft since 2004.
This new image from Cassini shows the anti-Saturn hemisphere of Tethys. North on Tethys is up and rotated 42 degrees to the right.
The image was taken in visible light with Cassini’s narrow-angle camera on April 11, 2015, from a distance of 118,000 miles (190,000 km) from Tethys.
