Surficial properties in Melas Chasma, Mars, from Mars Odyssey THEMIS data

We examine the nature of the surface layer in a small area of the Melas Chasma region as determined from high-resolution thermal and visible Mars Odyssey Thermal Emission Imaging System (THEMIS) data as well as how our conclusions compare to past analyses. At THEMIS resolution, the thermal structure is dominated by local control and all significant thermal variations can be linked to morphology. Thus, THEMIS provides us with detailed images that contain thermophysical information as well, allowing us to create a surficial geologic map intended to reflect the surface structure of the region. Eight units have been defined: (i) blanketed plateaus with thermally distinct craters and fractures, (ii) blanketed canyon walls with rocky edges, (iii) indurated and/or rocky canyon wall slide material partially covered by aeolian material, (iv) an anomalous wall region with fluvial-like depressions partially filled with particulate material, (v) indurated and/or rocky ridged and non-ridged canyon floor landslide material mingled with aeolian material, (vi) sand sheets, (vii) indurated and/or rocky rounded blocks intermingled with small areas of aeolian material, and (viii) transverse dunes. The THEMIS thermal data support conclusions from previous studies but also reveal much more structure than was seen in the past. We have found that all significant thermal variations in this region can be linked to morphology but all morphological variations cannot be linked to significant thermal variations. THEMIS visible images provide an intermediate resolution that bridges the gap between MOC and Viking and allow for a more meaningful interpretation of the geologic context of a region. Surfaces indicate that landslides were an important geologic process long ago, shaping the canyon walls and floor, while aeolian processes have subsequently altered the surface layer in many locations and may still be active.