Paper No. 178-4
Presentation Time: 9:00 AM-6:30 PM
INFERRING THE COMPOSITION AND MECHANICAL PROPERTIES OF THE NEAR-SURFACE OF CERES FROM EMPLACEMENT MODELING OF LAYERED/PANCAKE-LIKE EJECTA DEPOSITS
HUGHSON, Kynan H.G.1, RUSSELL, Christopher T.2, SCHMIDT, Britney E.3, CHILTON, Heather4, SCULLY, Jennifer E.C.5, SIZEMORE, Hanna G.6, BYRNE, Shane7, PLATZ, Thomas8 and RAYMOND, Carol A.5, (1)Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, (2)Earth and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East, Los Angeles, CA 90095, (3)Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, (4)School of Earth & Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332, (5)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, (6)Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719-2395, (7)Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, (8)Max Planck Institute for Solar System Research, Göttingen, 37077, Germany, p151c@ucla.edu
During the Survey, High Altitude Mapping Orbit, and Low Altitude Mapping Orbit phases of the primary mission Dawn’s Framing Camera observed a multitude of globally distributed lobate deposits. These flows were broadly interpreted as either similar to ice-cored/ice-cemented flows (Type 1 flows) on Earth and Mars, long run-out terrestrial or martian landslides (Type 2 flows), or highly mobile fluidized ejecta-like deposits (Type 3 flows) (Buczckowski et al., 2016; Schmidt et al., 2017). The Type 3 flows are morphologically similar to layered/pancake ejecta found on Mars and Ganymede where they are thought to be caused by impacts into ground ice rich substrates (Mouginis-Mark, 1979; Boyce et al., 2010). The main structural difference between these putative cerean fluidized ejecta flows and their martian/ganymedean counterparts is that the latter tend to form full aprons around the entire circumference of their parent crater, while the former generally only occur around a fraction of the circumference (usually < 180º) of their parent crater.
We assess the effects of target material strength, sliding friction, and vapor entrainment on the production of these features by comparing the ejecta mobility (EM: the ratio of the radius of the ejecta blanket to the radius of the parent crater) values for all Type 3 cerean flows to a ballistic/kinematic sliding model similar to the one developed by Weiss et al. (2014) to model EM for impacts into a variety of ground ice rich substrates of differing volatile content on Mars. Initial results suggest that, in order for these features to form, the cerean surface requires a large coefficient of sliding friction (>0.1), and that significant amounts of water be vaporized during impact. However, the model does not tightly constrain the strength of the target material (best-fit values range from granite-like to unconsolidated-sand-like). These results are consistent with a largely dry, rough, and thin surface layer underlain by material rich in pore-filling ground ice, even at low latitudes. Future implementation of this model will further incorporate compositional and geophysical knowledge attained from Dawn in order to better constrain the strength of the cerean surface.
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