GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 246-8
Presentation Time: 9:50 AM


TRUSSELL, Allyson R.1, GOLOMBEK, Matthew P.2, CHARALAMBOUS, Constantinos3, HAUBER, Ernst4, WARNER, N.H.5, WEITZ, Catherine M.6, WILLIAMS, Nathan R.7 and PIKE, W.T.3, (1)Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, (2)Department of Geological Sciences, SUNY Geneseo, 1 College Circle, Geneseo, NY 14454, (3)Department of Electrical and Electronic Engineering, Imperial College, London, United Kingdom, (4)DLR Deutsches Zentrum für Luft- und Raumfahrt, Berlin, Germany, (5)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, (6)Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, (7)Jet Propulsion Laboratory, California Institute of Technology, M/S 183-301, 4800 Oak Grove Dr., Pasadena, CA 91109

The InSight mission (Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport) landed successfully on November 26, 2018 in western Elysium Planitia on Mars. Using stereo images from InSight’s Instrument Deployment Camera (IDC), we quantify the size-frequency distribution of the rocks nearby the lander. Measurements were made by fitting a convex hull in ArcMap for each visible rock with topography from stereoscopic coverage. The rock’s two horizontal axes from the convex hull fit were averaged together to yield a rock diameter. From this diameter and the area of the region surveyed, we determine the cumulative fractional area (CFA) and cumulative number of the rocks versus diameter. Three new counts were made over 5-8 m2 areas in the rockier portion of the landed surface (one to the southeast and two to the north-northwest). Rocks counted are <20 cm diameter and for diameters >5 cm the distributions are similar in slope to exponential rock abundance models used to describe rock populations for landing spacecraft for CFAs of 1-4%. These CFAs are similar to those determined from previous counts of less rocky (smooth) areas near the workspace to the south for diameters >5 cm. The smooth areas are pebble and granule rich with steeper slopes than the exponential models for diameters <4 cm. The two counts to the north-northeast are very similar to the Phoenix landing site (2% CFA) and the area to the south is very similar to the Spirit landing site (4%) for diameters >4 cm. The steep slopes of the InSight distributions at diameters <4 cm are also similar to the Phoenix and Spirit landing sites. Rock abundances measured from the lander are consistent with expectations based on orbital remote sensing data. Counts of rocks in HiRISE images from their shadows and fits to their size-frequency distributions indicate 1-6% of the landing ellipse is covered by rocks. These low rock abundances are also consistent with thermal differencing estimates of rock abundance (3-4%).