Ithaca Chasma

Ithaca Chasma is a valley on Saturn's moon Tethys. It is 100 km wide, 3 to 5 km deep and 2,000 km long, running approximately three-fourths of the way around Tethys' circumference. It is named after the island of Ithaca, in Greece. [ [http://planetarynames.wr.usgs.gov/jsp/FeatureTypesData2.jsp?systemID=6&bodyID=14&typeID=6&system=Saturn&body=Tethys&type=Chasma,%20chasmata&sort=AName&show=Fname&show=Lat&show=Long&show=Diam&show=Stat&show=Orig Tethys Nomenclature: Chasma, chasmata] - USGS Astrogeology Research Program]

It is thought 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. Earlier craters made before Tethys solidified were probably all erased by geological activity before then.

Tethys' subsurface ocean may have resulted from a 2:3 orbital resonance between Dione and Tethys early in the solar system's history. 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. [cite conference
first = E. M. A.
last = Chen
authorlink =
coauthors = Nimmo, F.
title = Thermal and Orbital Evolution of Tethys as Constrained by Surface Observations
booktitle = Lunar and Planetary Science XXXIX (2008)
pages =
publisher =
date = March 2008
location =
url = http://www.lpi.usra.edu/meetings/lpsc2008/pdf/1968.pdf
doi =
id =
accessdate = 2008-03-14] [cite web
last = Rincon
first = Paul
authorlink =
coauthors =
title = Saturn moon 'once had ocean'
work = BBC News web site
publisher = BBC
date = 2008-03-14
url = http://news.bbc.co.uk/2/hi/science/nature/7297408.stm
format =
doi =
accessdate = 2008-03-14]

An alternative hypothesis is that it was formed at the same time as the large crater Odysseus which is on the opposite side of the moon. When the impact that created Odysseus occurred, the shockwave may have traveled through Tethys and fractured the icy, brittle surface on the other side.

References