POLYGONAL IMPACT CRATERS ON URANIAN SATELLITES REVEAL HIDDEN TECTONISM (Invited Presentation)

Polygonal impact craters (PICs) are found on the surfaces of planetary bodies throughout the Solar System. PICs are craters that have at least one straight rim segment. Analysis of the morphology of PICs, and the orientation of their straight rim segments can be used to infer sub-regolith and/or sub-resolution fracture orientations, thereby providing new insight into the tectonic histories of planetary bodies where visible fractures are absent. This technique is particularly useful for investigating tectonism on planetary bodies where only limited imaging data exists with moderate to low spatial resolution. We applied our PIC analysis technique to the mid-sized Uranian satellites Miranda and Ariel that were imaged during the Voyager 2 flyby of Uranus (best spatial resolution ~0.25 km/pixel and ~1 km/pixel, respectively).

On Miranda, some PICs are located on Elsinore Corona, as well as in the surrounding cratered terrain. The PICs on Elsinore do not follow the E-W orientations of the ridges within Elsinore’s bounding terrain, indicating that these ridges are not underlain by deep-rooted, sub-vertical normal or strike-slip faults. Instead, Elsinore’s ridges may be contractional features, consisting of folds and/or thrust faults, or cryovolcanic features without fault structures. Furthermore, the PICs in this region indicate that a NW oriented fracture system is present over much of Miranda’s trailing hemisphere. Based on cross cutting relationships with ancient, subdued craters, the NW fracture system is older than Elsinore. Elsewhere on Miranda, three PICs are present proximal to the massive scarp Verona Rupes. These PICs exhibit N-S orientations consistent with the surrounding fractures of Miranda’s Global Rift System. However, this fracture system also overprints Elsinore Corona, suggesting reactivation of the NW fractures after Elsinore formed.

On Ariel, PICs with NW-SE orientations are present in the Cratered Plains in between, Sylph, Korrigan, and Pixi Chasmata. The orientations of these PICs suggest that a previously unrecognized fracture system is present within this terrain. The inferred fractures are sub-parallel to Kra Chasma, supporting the interpretation that this feature is bound by faults.