Normal Faults on Ceres: Insights Into the Mechanical Properties and Thermal History of Nar Sulcus

Abstract

We characterized two sets of extensional faults that comprise the Nar Sulcus region of Ceres by applying a cantilever model for fault related flexure and derived flexural rigidity values for Nar Sulcus between 2.0 · 1015 and 1.8 · 1016 N·m. This range of flexural rigidity makes Nar Sulcus mechanically akin to extensional structures on Ganymede, Europa, and Enceladus. We combine these observations with an inferred strength profile for the upper mechanical layer of Ceres and estimate its thickness to be 2.9–9.5 km. Surface heat fluxes at Nar Sulcus during its formation were likely ≥10 mW/m2 for estimated strain rates of 10−17–10−14 s−1, which is at least one order of magnitude larger than the current estimated global average. For geologically plausible heat fluxes between 10 and 100 mW/m2, we estimate an upper bound of ~30 vol.% mechanically silicate‐like phases in the near surface at Nar Sulcus, neglecting the effects of porosity.

Fluidized Appearing Ejecta on Ceres: Implications for the Mechanical Properties, Frictional Properties, and Composition of its Shallow Subsurface

“…From the measurement and deviation of ε alone it is difficult to estimate the ground ice content of the substrate, but we do conclude that the substrate near these FAE, under impact cratering strain rates, mechanically behaves more like a ground ice rich ice‐silicate mixture, and/or an extremely unconsolidated material, than competent rock. This is consistent with the low flexural rigidity reported by Hughson et al (), for the Cerean crust near Nar Sulcus, and the low simple‐to‐complex transition diameter for impact craters observed by Hiesinger et al (), which have been interpreted to make Ceres more mechanically akin to outer solar system icy satellites than terrestrial planets.…”

Science Drivers for the Future Exploration of Ceres: From Solar System Evolution to Ocean World Science

“…These include long-runout landslides, low-mobility viscous flows (Figure 5(d) and (e)), and ejecta that appears to be fluidized (Figure 5(f)). The mobility regimes of these observed mass movements suggest that the crust is an intimate mixture of rock and ice that can behave in both viscous and inviscid manners, depending on the degree of melting and strain rate (Schmidt et al 2017;Hughson et al 2018). Additionally, high-resolution imagery and terrain models from Dawn's final extended mission revealed an abundance of small quasi-conical hills on the floor of Occator crater (Figure 5(g)).…”

“…Tectonic processes likely also occur on Ceres (e.g., Bland et al 2019;Ruiz et al 2019), although the mechanisms involved are not well understood. Geologic processes on Ceres including extensional tectonics (Figure 5(i); Hughson et al 2018), landslides, and other material flows (Figures 5(d)-(f); e.g., Schmidt et al 2017;Hughson et al 2019), as well as cryohydrologic features (Figure 5(g); Schmidt et al 2020), may involve a mixture of silicates, ice, and water common to glacial environments on the Earth and Mars. Other authors (Johnson & Sori 2020) have argued that mass-wasting features on Ceres do not inform us about local ice content or shallow compositional structure and instead are strongly controlled by topography.…”

Planetary Caves: A Solar System View of Processes and Products

“…This implies that processes like subsurface fluid transport, mantle convection, and solid‐state diapirism were likely active in the geologic past. Additionally, ice‐related diapirism and extension may also be responsible for the Nar Sulcus features (Figure 5a) in the southern hemisphere, which are a set of large fractures that may be imbricated normal faults (Hughson, Russell, Schmidt, Travis, et al., 2019). Furthermore, ice sublimation, hydrologic, and cryovolcanic processes are hypothesized to govern the creation of large edifices (e.g., Ahuna Mons; Ruesch et al., 2016) and pitted terrains (Sizemore et al., 2019).…”

“…Yet the prospect for identifying such features based on existing data is extremely limited. At least one presumed cryovolcanic caldera identified as a SAP (Crown et al, 2018 ;Hughson, Russell, Schmidt, Chilton, et al, 2019;Hughson, Russell, Schmidt, Travis, et al, 2019); other features requiring further examination include impact fractures and pitted terrain within at least seven craters and presumed tectonic fractures in at least three regions Europa Identification Tectonic fracturing, cryovolcanic? Six plumes (i.e., potential geysers), a fracture, and a fracture network detected (Roth et al, 2014(Roth et al, , 2016Sparks et al, 2016;Paganini et al, 2019; this study); an additional undetermined number of large fractures require further study Titan Identification/Characterization Methane-based dissolution with suffosion, sublimation, cryovolcanic, and tectonic fracturing 1,270 SAPs in organic sedimentary deposits identified (Malaska, Schoenfeld, et al, 2022) Enceladus Identification/Characterization Tectonic fracturing, suffusion, cryovolcanic?…”