Editing Ithaca Chasma (section)

== Origin ==
There are two basic hypothesis as to how Ithaca Chasma formed. One of them is that it formed as Tethys's internal global liquid salt water ocean solidified, causing the moon to expand and cracking its surface to accommodate the extra volume within.{{sfn|Moore Schenk et al.|2004|pp=424–30}} Earlier [[Impact crater|crater]]s made before Tethys solidified were probably all erased by geological activity before then.{{sfn|Giese|Wagner|Neukum|Helfenstein|2007}}

Tethys's global subsurface ocean may have resulted from a 2:3 [[orbital resonance]] between this moon and [[Dione_(moon)|Dione]] early in the Solar System's history. The resonance would have led to [[orbital eccentricity]] and [[tidal heating]] that may have warmed Tethys's interior enough to form the ocean. Subsequent freezing of the internal ocean after the moons escaped from the resonance may have generated the extensional stresses that created Ithaca Chasma.{{sfn|Chen|Nimmo|2008}}{{sfn|Rincon|2008}}

An alternative [[hypothesis]] is that it was formed at the same time as the large crater Odysseus which lies near a pole of the Ithaca Chasma. When the impact that created Odysseus occurred, the shockwave may have traveled through Tethys and produced a [[circumcircular]] fracture analogous to outer ring graben of multiring impact basins.{{sfn|Moore Schenk et al.|2004|pp=424–30}} 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.{{sfn|Jaumann Clark et al.|2009|pp=645–46}}
{{clear}}