Tethys
What is Tethys?
Moons· Diameter 1,062 km. A moon of Saturn made almost entirely of water ice. It bears a huge crater, Odysseus, and a canyon, Ithaca Chasma, that runs three-quarters of the way around it.
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Orbit and size
| Diameter | 1,062 km |
|---|---|
| Distance from Saturn | 294,600 km |
| Orbit | 1.89 d |
| Note | almost pure water ice, giant Ithaca Chasma |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Parent planet and sibling moons
Telesto and Calypso, the two companions on Tethys's orbit
Telesto and Calypso are small moons that share Tethys's orbit. Telesto travels 60 degrees ahead of Tethys and Calypso 60 degrees behind. At these two points the pulls of Saturn and Tethys balance out, so a small body can stay there for a very long time without being pushed away. Moons in such positions are called Trojan moons.
Both were found with telescopes on Earth in 1980. Telesto is about 25 km across and Calypso about 21 km, roughly a fiftieth the size of Tethys. In pictures from the Cassini spacecraft their surfaces look strangely smooth, with crater rims softened by a coat of fine ice dust. Scientists think the dust is made of ice grains from Saturn's E ring that keep settling on them.
The place names on Tethys come from Homer's Odyssey. The largest crater is named after the hero Odysseus and the great canyon after his home island, Ithaca. The moon itself is named for Tethys, a Titan goddess of Greek myth, following John Herschel's proposal in 1847 to name Saturn's moons after the Titans.
The moon in depth
Tethys is a moon of Saturn. Giovanni Cassini discovered it in 1684, the same year he found its neighbour Dione. It is 1,062 km across, a little less than the distance from New York to Chicago (about 1,150 km), and it circles Saturn at about 295,000 km, taking 1.89 days, a little under two days, for each lap. Its density is almost exactly that of water, so scientists think it is made mostly of ice.
Two huge features stand out on its surface. One is Odysseus, a crater 450 km wide, which is 40 percent of the moon's diameter. The other is Ithaca Chasma, a canyon 100 km wide and 3 to 5 km deep, much deeper than the Grand Canyon in the United States at about 1.8 km. Scientists think the crust may have split when water inside the moon froze and expanded.
Follow Saturn in the orbit view to see the path of Tethys, with Mimas and Enceladus inside it and Dione outside. Because its surface is clean ice, Tethys reflects sunlight very well; among Saturn's moons only Enceladus reflects a larger share. That is why a small telescope on Earth can show it as a faint dot of light beside Saturn.
Frequently asked
- How big is Tethys?
- The diameter of Tethys is 1,062 km.
- How far is Tethys from Earth?
- The distance from saturn of Tethys is 294,600 km.
- What is notable about Tethys?
- The note of Tethys is almost pure water ice, giant Ithaca Chasma.
- Which planet does Tethys orbit?
- Tethys orbits Saturn.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.