via National Geographic, a new study looking at Saturn's moon Tethys appears to have found evidence the satellite once held an underground ocean, and that there still may be water remaining on it. Tehtys hasn't undergone much scrutiny due to its "regular old moon" appearance, but a huge rift on the stallite may indicate something interesting was afoot many years ago.
"Tethys, Saturn's fifth largest moon, hasn't drawn much attention from astronomers because unlike the planet's other moons, it seems surprisingly ordinary, the researchers said.
"It was geologically active in the past, but it's not doing anything interesting today," said study co-author Francis Nimmo, a planetary scientist at the University of California, Santa Cruz. But the 662-mile-wide (1,066-kilometer-wide) moon hasn't always been quiescent. Billions of years ago tectonic forces produced an enormous rift similar to the East African Rift Valley on Earth, Nimmo said.
The rift on Tethys is about 620 miles (1,000 kilometers) long, 62 miles (100 kilometers) wide, and 3 to 6 miles (5 to 10 kilometers) deep. "[It] cuts across almost half the satellite," he said. Nimmo and his graduate student, Erinna Chen, believe that the energy required to make such a rift is evidence that Tethys once hosted an ocean.
The team was examining the rift formation and found the energy required to create it is difficult to explain from the tidal forces generated on the moon by Saturn without the interior of the moon being a liquid. An underground ocean is the likliest explanation, allowing the moon's crust to flex more than if the moon was solid throughout. With the confirmation of water on Tethys, it would be the fifth outer solar moon known to contain water - Jupiter's moons Callisto and Europa, and fellow Saturnian moons Titan and Enceladus are the others.