Fracture geometry and statistics of Ceres’ floor fractures

Floor-fractured craters are one of the most distinct features on Ceres. Most of the fractures are located on the crater floors. The floor-fractures are concentric, radial or polygonal and share similarities with the floor-fractured craters (FCC) of Class 1 and 4 on the Moon (e.g., Buczkowski et al., 2018; Schultz, 1976) In total we measured 2336 fractures in thirteen craters. We analyzed their width, length, orientation and density. Floor-fractures on Ceres do not show a global uniform sense of orientation. Nevertheless, two or more preferred orientations can be found in nearly every crater. The density map illustrates that there is typically no decrease of fracturing from the crater center to the crater rim and denotes formation mechanisms that are not necessarily impact driven. Because of the variation in these parameters, it is more likely that FFC on Ceres are globally independent and show different formation mechanisms. The geometry of the floor-fractures suggests an inhomogeneous, brittle surface material, in some cases with volatile components. We also propose that the formation mechanisms on Ceres are comparable to those on the Moon and Mars and such mechanisms include cooling/melting processes, degassing, and subsidence of the crater floor by up-doming of subsurface material as a result of absolute tensile stresses

Delivery of Dark Material to Vesta via Carbonaceous Chondritic Impacts

NASA's Dawn spacecraft observations of asteroid (4) Vesta reveal a surface with the highest albedo and color variation of any asteroid we have observed so far. Terrains rich in low albedo dark material (DM) have been identified using Dawn Framing Camera (FC) 0.75 {\mu}m filter images in several geologic settings: associated with impact craters (in the ejecta blanket material and/or on the crater walls and rims); as flow-like deposits or rays commonly associated with topographic highs; and as dark spots (likely secondary impacts) nearby impact craters. This DM could be a relic of ancient volcanic activity or exogenic in origin. We report that the majority of the spectra of DM are similar to carbonaceous chondrite meteorites mixed with materials indigenous to Vesta. Using high-resolution seven color images we compared DM color properties (albedo, band depth) with laboratory measurements of possible analog materials. Band depth and albedo of DM are identical to those of carbonaceous chondrite xenolith-rich howardite Mt. Pratt (PRA) 04401. Laboratory mixtures of Murchison CM2 carbonaceous chondrite and basaltic eucrite Millbillillie also show band depth and albedo affinity to DM. Modeling of carbonaceous chondrite abundance in DM (1-6 vol%) is consistent with howardite meteorites. We find no evidence for large-scale volcanism (exposed dikes/pyroclastic falls) as the source of DM. Our modeling efforts using impact crater scaling laws and numerical models of ejecta reaccretion suggest the delivery and emplacement of this DM on Vesta during the formation of the ~400 km Veneneia basin by a low-velocity (<2 km/sec) carbonaceous impactor. This discovery is important because it strengthens the long-held idea that primitive bodies are the source of carbon and probably volatiles in the early Solar System.Comment: Icarus (Accepted) Pages: 58 Figures: 15 Tables:

Enabling and Enhancing Science Exploration Across the Solar System: Aerocapture Technology for SmallSat to Flagship Missions

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Martian Araneiforms: A Review

Araneiforms are enigmatic dendritic negative topography features native to Mars. Found across a variety of substrates and exhibiting a range of scales, morphologies, and activity level, they are hypothesized to form via insolation-induced basal sublimation of seasonal CO2 ice. With no direct Earth analog, araneiforms are an example of how our understanding of extant surface features can evolve through a multipronged approach using high resolution change-detection imaging, conceptual and numerical modeling, and analog laboratory work. This review offers a primer on the current state of knowledge of Martian araneiforms. We outline the development of their driving conceptual hypothesis and the various methodologies used to study their formation. We furthermore present open questions and identify future laboratory and modeling work and mission objectives that may address these questions. Finally, this review highlights how the study of araneiforms may be used as a proxy for local conditions and perhaps even past seasonal dynamics on Mars. We also reflect on the lessons learnt from studying them and opportunities for comparative planetology that can be harnessed in understanding unusual features on icy worlds that have no Earth analog

A Reconnaissance Strategy for Landing on Europa, Based on Europa Clipper Data

No abstract available

The geology of the Nawish quadrangle of Ceres: The rim of an ancient basin

Herein we present the geology of the Nawish quadrangle, located in the equatorial region of dwarf planet Ceres, named after one of the most prominent craters of the area. Geologic mapping was based on the image mosaics and digital terrain models derived from Dawn Framing Camera data. Interpretation of geologic units was supported by supplemental data, such as the multi spectral color images from the Framing Camera, and the spectral parameters derived from the Visible and Infrared Spectrometer (VIR) data, as well as Dawn gravity data. There is not a primary feature that dominates the geology of Nawish quadrangle, but rather several terrains overlap, and their relations explain the geology of the area. Crater size frequency distributions show that Nawish quadrangle is dominated by two distinct time domains. The central and eastern part of the quadrangle is topographically elevated, which we define as cratered highlands, and contains the older domain. The western lowlands show two younger domains related to impact craters Kerwan and Dantu, including the Kerwan smooth material and Dantu ejecta. This variation of elevation within the Nawish quadrangle is more than the half of the global topographic altitude variation on Ceres. Analysis and comparison of the topography of the Nawish quadrangle with surrounding ones shows that this quadrangle is dominated by the topography of the rim sector of a large, >800 km ancient impact basin, most likely the putative Vendimia Planitia. The Nawish quadrangle thus represents a sector of Ceres which has not undergone large-scale, post-Kerwan, intermediate age-events, but rather represents a place on Ceres where a well-preserved relict of old cerean crust can be studied, together with ejecta from more recent impact events