Abstract
Global distribution of bedrock exposures on Mars using THEMIS high-resolution thermal inertia
Mars Space Flight Facility, School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA
Mars Space Flight Facility, School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
U.S. Geological Survey, Flagstaff, Arizona, USA
We investigate high thermal inertia surfaces using the Mars Odyssey Thermal Emission Imaging System (THEMIS) nighttime temperature
images (100 m/pixel spatial sampling). For this study, we interpret any pixel in a THEMIS image with a thermal inertia over
1200 J m−2 K−1 s−1/2 as “bedrock” which represents either in situ rock exposures or rock-dominated surfaces. Three distinct morphologies, ranked
from most to least common, are associated with these high thermal inertia surfaces: (1) valley and crater walls associated
with mass wasting and high surface slope angles; (2) floors of craters with diameters >25 km and containing melt or volcanics
associated with larger, high-energy impacts; and (3) intercrater surfaces with compositions significantly more mafic than
the surrounding regolith. In general, bedrock instances on Mars occur as small exposures (less than several square kilometers)
situated in lower-albedo (<0.18), moderate to high thermal inertia (>350 J m−2 K−1 s−1/2), and relatively dust-free (dust cover index <0.95) regions; however, there are instances that do not follow these generalizations.
Most instances are concentrated in the southern highlands, with very few located at high latitudes (poleward of 45°N and 58°S),
suggesting enhanced mechanical breakdown probably associated with permafrost. Overall, Mars has very little exposed bedrock
with only 960 instances identified from 75°S to 75°N with likely <3500 km2 exposed, representing
1% of the total surface area. These data indicate that Mars has likely undergone large-scale surface processing and reworking,
both chemically and mechanically, either destroying or masking a majority of the bedrock exposures on the planet.
Received 12 February 2009; accepted 21 July 2009; published 4 November 2009.
Citation: (2009), Global distribution of bedrock exposures on Mars using THEMIS high-resolution thermal inertia, J. Geophys. Res., 114, E11001, doi:10.1029/2009JE003363.
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