Floor Fractures in Ezinu Crater: Evidence of Solid State Flow on Ceres?

Ezinu, a 116 km crater located at 43.2ºN, 195.7ºE on Ceres, hosts a set of floor fractures. The primary trough is arcuate in shape, curving strongly to the east; it is 22.7 km long, 2.6 km wide, and up to 200 m deep. This trough wraps around a roughly circular topographic high that rises 514 m above the crater floor. Smaller fractures splay out from the primary trough mainly to the east, across the topographic high, while a few horsetail splays extend to the south from the western side of the trough. We suggest that these fractures may have formed as a result of the solid state flow of a low viscosity and low density (LV-LD) material, driven by differential loading and buoyancy.

The solid state flow model for Ceres [Bland et al., 2018] suggests that differential loading is brought about by the sudden removal of an overlying layer due to impact cratering. Preliminary models show that an impact into the edge of a layer of LV-LD material (presumably a mixture of ice, salts, and clathrate) within the Ceres crust can result in surface deformation of the crater wall [Bland et al., 2018]. Physical modeling of analog lobate flows suggests that the fractures in Ezinu might have formed as subsurface LV-LD material flowed into the crater.

Ezinu impacted into the northwestern flank of Hanami Planum, the only large discrete topographic rise on Ceres. This might explain why the eastern floor of Ezinu is generally higher than the western floor. However, it is also possible that the general raising of the crater floor in this area is due to an injection of a LV-LD material. In fact, since one hypothesis for the formation of Hanami Planum itself has been the intrusion of a lower density material [Scully et al., 2017], it might even be the source of LV-LD material.

There is a 13.6 km diameter crater within Ezinu that has been classified as a Class 4 floor-fractured crater [Buczkowski et al., 2018]. If an intrusion of LV-LD material resulted in the Ezinu fracturing, then it would most likely also cause the uplift of the floor and creation of subtle fractures within this smaller crater. It is possible that the moat observed within this crater is due to the impact melting of the ice within the LV-LD layer, creating a cryomagmatic sill that would inflate as it refroze, causing uplift of the floor. Further physical and numerical analyses are planned to better constrain the interpretation.