Crater-related flow features on Ceres - Implications for cryovolcanism

Abstract

Some craters on Ceres show post-impact modifications, like the deposition of extended plains laced with pits, lobate flows, and ponded material [1]. We found those features on craters with a bluish spectral signature, such as Haulani, Ikapati, Occator and Kupalo. Lobate flows of Haulani and Kupalo originating from the crest of the central ridge [1,2] partly overwhelming the mass wasting deposits from the rim, indicating possible post-impact resurfacing processes [3,4]. The drop height-to-runout length ratio of several flow features of the four craters reveals a coefficient of friction of < 0.1, implying higher flow efficiency for flows on Ceres than for similar features on other planetary bodies with similar gravity [1]. Therefore, we suggest a ductile material for the formation of those flows. Furthermore, the suggestion of an occurrence of ice within the Cerean crust [5] as well as possible salts incorporated into a regolith layer [3,4,5] indicates similar geological processes as seen on other icy bodies. Latest results by the Dawn Spacecraft indicates that Ceres is a weakly differentiated body containing a shell dominated by an ice-rock mixture [6] and ammoniated phyllosilicates [7]. Recent observations also show that hydrated salts could be warm enough to be mobile at a depth of 1.5-5 km below Ceres´ surface and would explain the buoyancy of ice and salt-enriched crustal reservoirs [8]. Therefore, it is likely that impacts hitting such reservoir layers triggered mobility and could have formed cryovolcanic features. Moreover, we assume that the plains and flow materials also originate from the subsurface and their release is triggered by impacts [3]. Additionally, the bluish material is mainly associated with the youngest impact craters on Ceres [9]. Thus, the post-impact modifications of the observed craters are formed by one of the youngest geologic processes on Ceres.