![]() ![]() K-H3O and Na-H3O jarosite solid solutions were synthesized under hydrothermal conditions. Jarosite is the first definitely discovered ferric sulfate mineral on Mars, indicating a highly acidic environment in Martian history. The top frame shows the initial condition, and highlights the extra. Results: Figure 2 shows some snapshots of two simulations of a 96 km diameter projectile impacting Ceres at 4 km s − 1 : one with a serpentine core (left hand side) and one with a dunite core (right hand side). ![]() Crater scaling for icy targets suggests that to form a final crater ∼ 700 km in diameter, a projectile composed of ice around one tenth the diameter of Ceres is required to impact at 4 km s − 1 (a typical impact velocity on Ceres ). A gravity field was assigned at the start of the calculation and, due to the large mass difference between the impactor and Ceres, was not updated during the calculation. Material was weakened after impact using the block model of acoustic fluidization. The silicate cores were assigned strength using the model described in, with parameters for dunite taken from the ice mantles were assigned strength using the model developed for icy satellites. iSALE was used in its 2D, axisymmetric formulation to reduce computational costs (thus impos- ing a normal incidence impact angle), although full 3D simulations are ongoing. A computational cell size of ∼ 3 km was used, which means that Ceres was represented by 160 cells across its radius. ![]() The size of the cores was calculated to give a mass, surface gravity and bulk density consistent with those estimated for Ceres. Impact modelling: The iSALE shock physics code was used to simulate impacts into different pos- sible internal structures for Ceres: (a) a dry silicate core with a radius of 369 km (using the ANEOS equation of state for dunite ) capped by an ice mantle (ANEOS equation of state for water), and (b) a hydrated silicate core of radius 426 km (using the ANEOS equation of state for serpentine ) capped by an ice mantle. in which the core will play a role during the opening of the transient crater, or the curvature of the surface is significant), further modelling is required. For small craters which form entirely in the ice mantle, this estimate is robust, but for larger craters (e.g. The model predicts around two craters larger than ∼ 700 km diameter. Figure 1 shows an estimate of the number of craters formed on Ceres using the crater scaling parameters for ice from. The expected number of craters on Ceres today will also be dependent on the internal structure, as crater relax- ation, especially near the equator, could remove evidence of craters > 4 km if they form in an ice layer. Over the same time period, on average Ceres would experience 3 impacts by objects one-twentieth its size (48 km), and have 1.3 impacts by objects one-tenth of its size (96 km). Over the course of solar system history, Ceres could expect over 63000 impacts of impactors 300 m in diameter or larger. The disruption threshold for Ceres was set using the criteria from, although after 10 4 simulations of Ceres’ impact history, no disruptive impacts occurred. The size- and velocity frequency distribution of impactors in the aster- oid belt were estimated using dynamical and collisional evolution models of terrestrial planet formation and as predicted for Ceres. ![]() Predicting impactor sizes: Using the statistical framework presented in, the number, sizes and velocities of impacts on Ceres were estimated. Here, we use a statistical model to predict the largest impacts expected on Ceres through solar system history, and explore how crater morphologies for such impacts vary with internal structure. With NASA’s Dawn due to enter orbit around Ceres soon, we will start receiving the first images of craters on the surface, which can be used to infer the nature of Ceres’ interior. These different structures will lead to different impact crater morphologies. Several different structures have been proposed, but the most prominent in the literature include either a dry or hydrated silicate core with an icy mantle. The internal structure of Ceres is un- known. ![]()
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