Ithaca Chasma

[1] Ithaca Chasma is a giant trough system about 3 km deep and approximately confined to a great circle running through the poles of Tethys.

One of them is that it formed as Tethys' internal global liquid salt water ocean solidified, causing the moon to expand and cracking its surface to accommodate the extra volume within.

[7] Tethys' global subsurface ocean may have resulted from a 2:3 orbital resonance between this moon and Dione early in the Solar System's history.

Subsequent freezing of the internal ocean after the moons escaped from the resonance may have generated the extensional stresses that created Ithaca Chasma.

[2] However, age determination based on crater counts in high resolution Cassini images showed that Ithaca Chasma is older than Odysseus, making the impact hypothesis unlikely.