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The relationship between fractures and impact craters on Tethys

Presentation #106.04 in the session Unmeltable Me, verse 2: Other Icy Satellites.

Published onOct 20, 2022
The relationship between fractures and impact craters on Tethys

Tethys, an inner moon of Saturn, bears evidence of past tectonic activity. The surface of the moon is covered with impact craters, consistent with many other outer solar system satellites. Tethys also has sets of linear features crossing the surface, including the large rift zone known as Ithaca Chasma. The origins of Ithaca Chasma and the other linear features are debated. Many theories suggest that freezing of a subsurface ocean applied forces to the surface of the moon, causing the observed features. However, this mechanism is not fully understood, and the linear features observed on the surface lack the random orientation that would be expected in such a scenario. Amongst the craters, rifts, and fractures, Tethys is also host to pit chains and features attributed to scouring from co-orbital debris. Notably, each of these features is either linear in nature, or related to impact cratering. In recent research we have observed a feature that is not linear, that no current theory explains. A curvilinear fracture, or perhaps a set of fractures forming a curve, has been observed west of Ithaca Chasma. The feature intersects with several small impact craters, but the fracture has no obvious association with a larger impact crater (e.g., a concentric crater fracture or crater floor fracture). A visually similar type of feature, cycloids, such as those observed on Europa, are thought to be a cyclical result of tidal forces. However, tidal forces are expected to be minimal on Tethys, and this fracture is the only feature of its nature thus far observed. To understand the origin of this feature, we are examining the relationship between fractures and craters on the surface of Tethys. Using ArcGIS and Cassini image data, we are mapping portions of the surface of Tethys and analyzing the correlation between the locations of craters and fracture features. While the curved feature is not well understood, we theorize that the craters intersecting the fracture may have paved the way for the formation of the fracture in some way. Understanding this curvilinear feature will provide insight into fracture formation on icy satellites without large tidal forces.

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