Tethys – Learn All About The Frozen Ice Moon

More Facts About Saturn’s Frozen Moon Tethys!

• Tethys was one of four Saturnian moons to be discovered by Giovanni Cassini (along with Dione, Rhea and Iapetus).
• Despite the moon being discovered in 1684, and initially being called Saturn III (being the 3^rd moon from Saturn), it wasn’t until 1847 that its name was changed to Tethys to avoid confusion after additional moons around Saturn were discovered.
• Tethys is similar to the neighbouring moons Rhea and Dione; they are all small, cold, cratered and airless bodies.
• Like all but two of Saturn’s major moons, Tethys is ‘tidally locked’ to Saturn as it orbits; meaning the same face of Tethys always faces Saturn. This is similar to Earth’s Moon!
• Tethys also shares its orbit with two much smaller trojan moons that are gravitationally bound at Tethys’ Lagrangian points; the trojan moon Telesto is ahead (L₄) and Calypso behind (L₅) by 60° respectively.
• Tethys is locked in resonance with the nearby inner moon Mimas, with these tidal (and rotational forces) squashing Tethys into the irregular shape of a triaxial ellipsoid!
• Tethys’ density is 0.97 times that of liquid water which suggests Tethys’ is composed of almost entirely water-ice and a small amount of rocky material!
• The small frozen moon has a mass less than 1% of Earth’s Moon.
• Tethys’ high water-ice content is evident from its high reflectivity (Albedo) and is the second brightest Saturnian moon after Enceladus.
• Images from the Cassini space probe also revealed that the trailing hemisphere is darker in colour due to the natural darkening which occurs to water-ice over millions of years as radiation alters its surface. The lighter-coloured leading hemisphere is ‘sand-blasted’ with young icy dust from Saturn's E-ring; formed from tiny particles ejected from Enceladus’ Tiger Stripes!
• Two major features dominate the cratered frozen geology of Tethys;
  • The 445 km (275 miles) wide Odysseus impact crater
  • And the valley called Ithaca Chasma which is 100 km wide, up to 5 km deep and extends for nearly 2000 km (which likely created as Tethys froze and expanded, cracking the frozen shell)
• A feature unique to Tethys is a series of curved red streaks on the moon's surface. They are a few kilometres wide and several hundred kilometres long. The red streaks are among the most unusual colour features found anywhere on Saturn's moons by the Cassini spacecraft. Their origin remaining a mystery. Weird isn’t it?!