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Saturn’s Moon Tethys

Saturn\'s moon Tethys. Image credit: NASA/JPL/SSI
Saturn’s moon Tethys is one of the 4 moons discovered by Giovanni Cassini in 1671-1684. It’s the 3rd furthest large moon from Saturn, and the 13th most distant moon over all.

You can also check out these cool telescopes that will help you see the beauty of planet Saturn.

Tethys measures 1066 km across, and orbits at an altitude of 295,000 km above the center of Saturn.

The density of Tethys is 0.97 grams per cubic centimeter. Since water is 1 g/cm3, this means that Tethys is comprised almost entirely of water ice (if you brought it closer to the Sun, the whole moon would evaporate away). This ice is very reflective, and makes Tethys relatively bright.

There are two different regions of terrain on Tethys. One portion is ancient, with densly packed craters, while the other parts are darker and have less cratering. Scientists think that Tethys was once internally active, with cryovolcanism that resurfaced parts of its surface.

The western hemisphere of Tethys is dominated by a huge crater called Odysseus. It’s 400 km across, making it 2/5th the size of Tethys itself.

Tethys has two co-orbital moons: Telesto and Calypso. These have been captured into Tethy’s Lagrangian points. One orbits ahead of Tethys, and the other follows behind.

Here’s a link to a story about Tethys, with a photograph taken by NASA’s Cassini spacecraft, and another about a feature on the surface of Tethys called Ithaca Chasma.

Want more info on Tethys? Check out this article from Solar Views, and this one from Nine Planets.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.


Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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