Ithaca Chasma

Fig. 4.14 Tethys, with Ithaca Chasma, a fracture vaUey that runs across Tethys. NASA/JPL/Space Science Institute...

On Tethys, a striking surface feature can be seen, a tremendous rift called Ithaca Chasma (see Fig. 4.14), which is 100 kilometers and runs nearly three-fourths of the way around the icy moon (Elder et al., 2007 [116]). One theory to explain the formation of this phenomenon is that Ithaca Chasma formed as Tethys internal liquid water solidified, causing the moon to expand and cracking its surface to accommodate the extra volume within (because water ice is less dense than liquid water). 

Tethys might have had a subsurface liquid ocean during its early history (Chen and Nimmo, 2008 [66]) when there was a 2 3 orbital resonance between Dione and Tethys. The resonance would have led to orbital eccentricity and tidal heating that may have warmed Tethys interior enough to form the ocean. Subsequent freezing of the ocean after the moons escaped from the resonance may have generated the extensional stresses that created Ithaca Chasma. 

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