Impact craters and their ejecta deposits offer insights into the structure and composition of planetary crusts. The 60 km diameter Hargraves Crater, Mars, demonstrates an unusual balance of exposure and preservation in its ejecta deposits. We investigated the morphologic, morphometric, thermophysical, and stratigraphic character-istics of the Hargraves Crater ejecta blanket. Our work shows that the crater produced two distinct ejecta units. The lower unit, He1, interpreted as a lithic impact breccia, is unsorted and composed of sub-angular clasts. These clasts in the breccia unit have a mean diameter of-10-12 m but range in size from m to km in size. The overlying unit, He2, is smooth, dark toned, comprises fewer and much smaller clasts (-1 m diameter on average at image resolution) and exhibits polygonal fracturing. We interpret this unit as an impact melt-bearing breccia or impact melt rock unit. A sharp contact is visible between the two ejecta units. These orbital observations are markedly similar to field observations of ejecta deposits on Earth. With the context of both in-situ and orbital impact studies, we interpret these two layers as a ballistic ejecta layer overlain by impact melt-rich flows and ponds. The two distinct layers, separated by a sharp contact, indicate two separate phases of ejecta emplacement. Hargraves Crater thus represents a unique opportunity to observe what may be a common ejecta blanket structure as other craters across the surface of Mars show similar characteristics. Future study of this "Hargraves-type" ejecta will improve our understanding of ejecta and ejecta emplacement processes.

MONTES, MARS. M. D. Lane, J. L. Bishop, D. Loizeau, D. Tirsch, L. L. Tornabene, L. Sacks, C. Viviano, J. R. C. Voigt Fibernetics LLC, Lititz, PA (lane@fibergyro.com), Carl Sagan Center, SETI Institute, Mountain View, CA, IAS, Université-Sud, Orsay, France, Institute of Planetary Research, German Aerospace Center (DLR), Berlin, Germany, Dept. of Earth Sciences, Institute for Earth and Space Exploration, University of Western Ontario, London, Canada, Johns Hopkins University Applied Physics Lab (JHUAPL), Laurel, MD, Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ.

Introduction: The prevalence of impact craters throughout the solar system correlates with their importance in the study of planetary surface processes, providing insights into the nature of: surface materials, crustal structures, surface age, and stratigraphy. In contrast to the Moon, the presence of an atmosphere and volatile-rich target rocks make Mars a comparable analogue to Earth impact studies. Numerous wellpreserved craters and extensive high-resolution image coverage augment the value of studying impacts on Mars. A prominent feature of impact craters through the solar system is the presence of ejecta deposits within and around the host crater (e.g., [1, 2]). High Resolution Imaging Science Experiment (HiRISE) images (25-30 cm/px) of Hargraves Crater on Mars provide detailed meter-scale observations of one of the bestexposed and well-preserved ejecta blankets on Mars (initially noted in [3]). Hargraves ejecta characteristically preserve exposures of materials consistent with melt-bearing and lithic breccia-bearing deposits [4]. Previous studies of impact craters and ejecta emplacement [e.g. [1, 2]] indicate that the preserved and exposed nature of the ejecta seen at Hargraves is indicative of some erosion but minimal post-impact deposition. The exposure of the preserved layers of the Hargraves ejecta blanket, unlike many ejecta blankets on Mars, permits an excellent means to study the deposition and emplacement processes of ejecta. In this work, we present the results of a detailed analysis of the Hargraves ejecta blanket with the HiRISE [5]. This study starts with the morphologic and general morphometric characterization of the features seen in ejecta to the south of the crater rim, in order to complement and expand on earlier studies of the ejecta deposited within the Nili Fossae “trough” to the west of Hargraves [4]. Hargraves Crater: Hargraves Crater is located in the Nili Fossae region of Mars at 20.76°N 284.36°W. The crater is ~68 km in diameter with a central uplift indicative of a complex morphology. Ejecta are deposited radially from the center of the crater, including into other nearby pre-existing structures where they are

We compare the thermophysical properties and particle sizes derived from the Mars Science Laboratory rover's Ground Temperature Sensor of the Bagnold dunes, specifically Namib dune, to those derived orbitally from Thermal Emission Imaging System, ultimately linking these measurements to ground truth particle sizes determined from Mars Hand Lens Imager images. In general, we find that all three datasets report consistent particle sizes for the Bagnold dunes (~110–350 μm and are within measurement and model uncertainties), indicating that particle sizes of homogeneous materials inferred from temperature measurements and thermophysical models are reliable. Furthermore, we examine the effects of two physical characteristics that could influence the modeled thermal inertia and particle sizes, including (1) fine‐scale (centimeter to meter scale) ripples and (2) thin layering of indurated/armored materials. To first order, we find that small‐scale ripples and thin (approximately centimeter scale) layers do not significantly affect the determination of bulk thermal inertia from orbital thermal data using a single nighttime temperature. Modeling of a layer of coarse or indurated material reveals that a thin layer (< ~5 mm; similar to what was observed by the Curiosity rover) would not significantly change the observed thermal properties of the surface and would be dominated by the properties of the underlying material. Thermal inertia and particle sizes of relatively homogeneous materials derived from nighttime orbital data should be considered as reliable, as long as there are no significant subpixel anisothermality effects (e.g., lateral mixing of multiple thermophysically distinct materials).