Landslides on Ceres: Diversity and Geologic Context.

Landslides are among the most widespread geologic features on Ceres. Using data from Dawn's Framing Camera, landslides were previously classified based upon geomorphologic characteristics into one of three archetypal categories, Type 1(T1), Type 2 (T2), and Type 3 (T3). Due to their geologic context, variation in age, and physical characteristics, most landslides on Ceres are, however, intermediate in their morphology and physical properties between the archetypes of each landslide class. Here we describe the varied morphology of individual intermediate landslides, identify geologic controls that contribute to this variation, and provide first-order quantification of the physical properties of the continuum of Ceres's surface flows. These intermediate flows appear in varied settings and show a range of characteristics, including those found at contacts between craters, those having multiple trunks or lobes; showing characteristics of both T2 and T3 landslides; material slumping on crater rims; very small, ejecta-like flows; and those appearing inside of catenae. We suggest that while their morphologies can vary, the distribution and mechanical properties of intermediate landslides do not differ significantly from that of archetypal landslides, confirming a link between landslides and subsurface ice. We also find that most intermediate landslides are similar to Type 2 landslides and formed by shallow failure. Clusters of these features suggest ice enhancement near Juling, Kupalo and Urvara craters. Since the majority of Ceres's landslides fall in the intermediate landslide category, placing their attributes in context contributes to a better understanding of Ceres's shallow subsurface and the nature of ground ice

Water induced sediment levitation enhances downslope transport on Mars

On Mars, locally warm surface temperatures (~293 K) occur, leading to the possibility of (transient) liquid water on the surface. However, water exposed to the martian atmosphere will boil, and the sediment transport capacity of such unstable water is not well understood. Here, we present laboratory studies of a newly recognized transport mechanism: “levitation” of saturated sediment bodies on a cushion of vapor released by boiling. Sediment transport where this mechanism is active is about nine times greater than without this effect, reducing the amount of water required to transport comparable sediment volumes by nearly an order of magnitude. Our calculations show that the effect of levitation could persist up to ~48 times longer under reduced martian gravity. Sediment levitation must therefore be considered when evaluating the formation of recent and present-day martian mass wasting features, as much less water may be required to form such features than previously thought

Post-impact thermal structure and cooling timescales of Occator Crater on Asteroid 1 Ceres

Occator crater is perhaps the most distinct surface feature observed by NASA's Dawn spacecraft on the Cerean surface. Contained within the crater are the highest albedo features on the planet, Cerealia Facula and Vinalia Faculae, and relatively smooth lobate flow deposits. We present hydrocode simulations of the formation of Occator crater, varying the water to rock ratio of our pre-impact Cerean surface. We find that at water to rock mass ratios up to 0.3, sufficient volumes of Occator's post-impact subsurface would be above the melting point of water to allow for the deposition of Faculae like deposits via impact-heat driven hydrothermal effusion of brines. This reservoir of hydrothermally viable material beneath the crater is composed of a mixture of impactor material and material uplifted from 10’s of kilometers beneath the pre-impact surface, potentially sampling a deep subsurface volatile reservoir. Using a conductive cooling model, we estimate that the lifetime of hydrothermal activity within such a system, depending on choice of material constants, is between 0.4 and 4 Myr. Our results suggest that impact heating from the Occator forming impact provides a viable mechanism for the creation of observed faculae, with the proviso that the faculae formed within a relatively short time window after the crater itself formed

No evidence for true polar wander of Ceres

The spins of solar system objects are not constant with time. One way a world’s spin can change is by true polar wander (TPW), whereby geological activity perturbs the moments of inertia, reorienting the entire body. Recently, Pasquale Tricarico used data from the NASA (National Aeronautics and Space Administration) Dawn mission to propose that Ceres experienced a large amount of TPW. Although their analysis is intriguing, we have identified several flaws that remove the central evidence for TPW of Ceres. Constraining the TPW of Ceres is critically important because TPW could have important consequences for Ceres’s geomorphology, tectonics and volatile content