Mathematics – Logic
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p21a0134r&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #P21A-0134
Mathematics
Logic
5470 Surface Materials And Properties, 6225 Mars, 6297 Instruments And Techniques
Scientific paper
As the two Mars Exploration Rovers 'Spirit' and 'Opportunity' traverse terrains within Gusev crater and at Meridiani Planum, respectively, they leave behind wheel tracks that are routinely imaged by the different sets of cameras as part of the MER Athena instrument suite. Stereo observations of these tracks reveal wheel rut depths which are diagnostic of the strength of the soil-like deposits crossed by the vehicles. This contribution will discuss results of systematic analyses of MER-A and -B wheel sinkage measurements with regard to solutions for soil bearing strength, cohesion, and friction angle, occurring in the context of a suite of physical properties studies that are part of the Athena science investigation. Sinkage data are analyzed with wheel-soil theory calibrated to the shape of the MER wheel while accounting for wheel slip and by consulting comparisons with terrestrial soils. Results are applicable to the top ~20 to 30 cm of the soil deposits 'sampled' by normal stresses incurred from the wheels. The large number of wheel track observations per distance travelled enables investigations of variations of soil physical properties as a function of spatial scale, type of surface feature encountered, and local topography. Exploiting relationships between soil strength and degree of soil consolidation known from lunar regolith and dry terrestrial soils allows one to relate inferred soil strengths to bulk density which in turn is related to dielectric properties and to fine-component thermal inertia, both of which have been constrained for the two MER landing sites by remote sensing with comparatively coarse spatial resolution. In the context of the Athena science investigation, physical properties studies contribute to an overall understanding of the geology at the landing sites as they i) allow comparisons to be made between physical and compositional properties, ii) support attempts to correlate materials with geologic units, iii) help identify stratigraphic relationships, and iv) contribute to identification of modification processes affecting the surface materials. Preliminary results support the identification of distinct types of soil deposits from their inferred, distinct strength characteristics. Bearing strengths derived for Gusev soils along the more than 3000 m long traverse from the lander to Columbia Hills West Spur vary between about 5 kPa and 200 kPa with significant scatter. Corresponding inferred bulk density ranges from roughly 1200 kgm-3 to 1500 kgm-3, and soil thermal inertia from about 134 J m-2 s-1/2 K-1 to 153 J m-2 s-1/2 K-1. At Meridiani Planum, soil deposits on the plains are more uniform in their physical properties than at the Gusev site, with variations introduced basically only by the distribution of aeolian bedforms. Meridiani plains soils - excluding the bedforms - show inferred bearing strengths between about 50 and 100 kPa (centered around 80 kPa), leading to a corresponding bulk density estimate of roughly 1300 kgm-3 and a soil thermal inertia of some 140 J m-2 s-1/2 K-1.
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