Tethys
What is Tethys?
Moons· Diameter 1,062 km. A Saturnian moon made of almost pure water ice — its density nearly matches water — scarred by the 450-km Odysseus crater and by Ithaca Chasma, a canyon wrapping three-quarters of the way around it. See its orbit just outside Enceladus in the orbit view.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
The orbit of Tethys at this moment: https://nowsky.org/solar/orbit?fw=moon:saturn:tethys&sp=0.006 — replayed live, no login.
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
Frequently asked
- How big is Tethys?
- 1,062 km.
- How far is Tethys from Earth?
- 294,600 km.
- What is notable about Tethys?
- almost pure water ice, giant Ithaca Chasma.
- Which planet does Tethys orbit?
- Saturn.
Telesto and Calypso, riding along with Tethys
Sixty degrees ahead of Tethys on its orbit travels Telesto (25 km across) and sixty degrees behind, Calypso (21 km). Both were found with ground-based telescopes in 1980, and in Cassini images their surfaces appear coated in fine ice dust that softens every crater — grains from Saturn's E ring apparently keep settling on them.
Tethys's two giant features may also be linked. One view holds that the impact which dug the 450 km Odysseus crater sent a shock through the moon and split open the Ithaca Chasma canyon on the far side; another, that the crust cracked as the interior froze and expanded. With a density 0.98 times that of water, Tethys is nearly pure ice, and either way it is a test of how much a ball of ice can take without breaking.
The moon in depth
Tethys was discovered by Cassini in 1684, the same year as Dione. It measures 1,062 km across, orbits 295,000 km from Saturn every 1.89 days, and with a density 0.98 times that of water it is essentially a ball of ice. Two small Trojan moons, Telesto and Calypso, share its orbit 60 degrees ahead and behind.
Two giant features dominate its surface. Odysseus crater is 450 km wide — 40% of the moon's diameter — and Ithaca Chasma is a canyon 100 km wide and 3–5 km deep stretching three-quarters of the way around the globe. The favored explanation is that an ancient internal ocean froze and expanded, cracking the crust. Cassini also found mysterious reddish arcs and a dark band painted by electrons from Saturn's magnetosphere.
Follow Saturn in the orbit view to find Tethys circling outside Mimas and Enceladus and inside Dione. It is bright enough that a small backyard telescope shows it as a tiny point of light beside Saturn.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.