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Physical Properties of Surface Materials
M. T. Mellon, Laboratory for Atmospheric & Space Physics, University of Colorado, Boulder, CO 80309-0392, USA,
R. L. Fergason, School of Earth & Space Exploration Arizona, State University, PO Box 876305 Tempe, AZ 85287-6305, USA,
N. E. Putzig, Laboratory for Atmospheric & Space Physics, University of Colorado, Campus Box 392 Boulder, CO 80309, USA
The thermal inertia of Mars is a physical property that controls the diurnal and seasonal cycles in surface temperature. It is defined as a function of the thermal conductivity, heat capacity, and density, all of which depend primarily on the physical structure of the surface layer. As such, thermal inertia provides information about the nature of the surface of Mars and the types of materials from which it is composed. Interpreting thermal inertia can be complicated by the variety of structures and material properties that result in the same thermal inertia value. In general, variations in the thermal conductivity have the greatest influence on the thermal inertia. Factors such as soil grain size, cementing or induration, rock abundance, the presence of bedrock, and surface heterogeneity all play an important role. The physical processes that effect the thermal conductivity are discussed to provide a framework from which thermal inertia of the Martian surface may be better understood.
Over the years, thermal inertia has been derived from numerous Earth-based and spacecraft temperature observations of Mars. In particular, thermal inertia from Viking, Mars Global Surveyor (MGS), and Mars Odyssey data has been derived and mapped with increasing spatial resolution, in each case providing an improved understanding of the surface layer. In addition, local-scale observations from the Mars Exploration Rovers (MERs) have provided in situ thermal inertia ground truth of characteristic soils and rocks. Overall, the surface of Mars is dominated by soils to a depth of a few centimeters or more.
Elemental Composition: Orbital and in situ Surface Measurements
W. C. Feldman, Los Alamos National Laboratory MS D466 Space & Atmospheric Science Los Alamos, NM 87545, USA,
M. T. Mellon, Laboratory for Atmospheric & Space Physics University of Colorado Boulder, CO 80309-0392, USA,
O. Gasnault, Laboratoire d'Astrophysique, 14 Avenue Belin Toulouse, 31400, France,
S. Maurice, Centre d'Etude Spatiale des Rayonnements, 9 Avenue du Colonel Roche BP 24346 Toulouse Cedex 4, France,
T. H. Prettyman, Los Alamos National Laboratory MS D466 Space and Atmospheric Science Los Alamos, NM 87545, USA
The Mars Odyssey Neutron Spectrometer (MONS) is described and its capabilities to detect and quantify deposits of H and CO2 ice within about 1 m of the surface are presented. After two Martian years in mapping orbit about Mars, two distinct domains of hydrogen deposits have been delimited. High-latitude domains in both hemispheres contain large, generally buried deposits of hydrogen and a near-equatorial domain contains more modest, yet significant, deposits. All observations are specified in units of water-equivalent hydrogen (WEH) and are compared with other observations of near-surface deposits of H2O and OH. They are also discussed in terms of theoretical models of volatile exchange between different water reservoirs through the atmosphere or through a system of aquifers. The CO2 ice cover of the residual cap near the South Pole is modeled and found not to be a significant part of the CO2 inventory of Mars.
Physical Properties of Surface Materials
M. P. Golombek, JPL MS 183-501 4800 Oak Grove Drive Pasadena, CA 91109, USA,
A. F. C. Haldemann, JPL 4800 Oak Grove Drive Pasadena, CA 91109, USA,
R. A. Simpson, Stanford University, David Packard #332 350 Serra Mall Stanford, CA 94305-9515, USA,
R. L. Fergason, School of Earth & Space Exploration Arizona State University, PO Box 876305 Tempe, AZ 85287-6305, USA,
N. E. Putzig, Laboratory for Atmospheric & Space Physics, University of Colorado, Campus Box 392 Boulder, CO 80309, USA,
R. E. Arvidson, Earth & Planetary Science, Washington University, St Louis, MO 63130, USA,
J. F. Bell III, Cornell University, Department of Astronomy, 402 Space Sciences Building, Ithaca, NY 14853-6801, USA,
M. T. Mellon, Laboratory for Atmospheric & Space Physics, University of Colorado – Boulder Boulder, CO 80309-0392, USA
Surface characteristics at the five sites where spacecraft have successfully landed on Mars can be related favorably to their signatures in remotely sensed data from orbit and from the Earth. Comparisons of the rock abundance, types and coverage of soils (and their physical properties), thermal inertia, albedo, and topographic slope all agree with orbital remote-sensing estimates and show that the materials at the landing sites can be used as “ground truth” for the materials that make up most of the equatorial and mid-latitude regions of Mars. The five landing sites sample two of the three dominant global thermal inertia and albedo units that cover ∼ 80% of the surface of Mars. The Viking Landers 1 and 2, Spirit, and Mars Pathfinder landing sites are representative of the moderate-to-high thermal inertia and intermediate-to-high albedo unit that is dominated by crusty, cloddy, and blocky soils (duricrust) with various abundances of rocks and bright dust. The Opportunity landing site is representative of the moderate-to-high thermal inertia and low-albedo surface unit that is relatively dust-free and composed of dark eolian sand and/or increased abundance of rocks. Interpretation of radar data confirms the presence of load bearing, relatively dense surfaces controlled by the soil type at the landing sites, regional rock populations from diffuse scattering similar to those observed directly at the sites, and root-mean-squared (RMS) slopes that compare favorably with 100 m scale topographic slopes extrapolated from altimetry profiles and meter scale slopes from high-resolution stereo images.
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