Nathaniel E. Putzig

A volcanic interpretation of Gusev Crater surface materials from thermophysical, spectral, and morphological evidence

[1]xa0Gusev Crater, the Mars Exploration Rover Spirit landing site (160 km diameter; 14.5°S, 184.5°W), has been identified in previous studies as a prime site of geological and exobiological interest on the basis of its potential for having hosted a fluviolacustrine environment; such environment may have been favorable for the development of biological activity. The origin and nature of the materials present at the surface of Gusev Crater are still being debated. In previous studies based on geomorphological and thermophysical data, surface materials in the crater have been interpreted as originating from fluviolacustrine, volcanic, or aeolian processes, or combinations thereof. We present results from the analysis of newly compiled thermophysical (Thermal Emission Spectrometer (TES) and Thermal Emission Imaging System (THEMIS)), spectroscopic (TES), and visible (THEMIS and Mars Observer Camera) data for the Gusev region. These data were analyzed using a new mosaicking technique developed to match the values of contiguous scenes and to produce seamless mosaics apt for geological interpretation. Thermophysical, spectroscopic, and morphological evidence point to the presence of local outcrops of lava flows of basaltic composition, materials consistent with a regolith developed from basaltic materials, fine-grained deposits of basaltic composition strongly modified by wind erosion, and wind deposits. According to these findings, we conclude that most of the materials occupying the present surface of Gusev have characteristics consistent with those of volcanic and aeolian deposits. Fluviolacustrine deposits proposed by other authors may exist under the volcanic materials and may be exposed in impact craters.

Thermophysical properties of the MER and Beagle II landing site regions on Mars

[1]xa0We analyzed remote-sensing observations of the Isidis Basin, Gusev Crater, and Meridiani Planum landing sites for Beagle II, MER-A Spirit, and MER-B Opportunity spacecraft, respectively. We emphasized the thermophysical properties using daytime and nighttime radiance measurements from the Mars Global Surveyor (MGS) Thermal Emission Spectrometer and Mars Odyssey Thermal Emission Imaging System (THEMIS) and thermal inertias derived from nighttime data sets. THEMIS visible images, MGS Mars Orbiter Camera (MOC) narrow-angle images, and MGS Mars Orbiter Laser Altimeter (MOLA) data are incorporated as well. Additionally, the remote-sensing data were compared with ground-truth at the MER sites. The Isidis Basin surface layer has been shaped by aeolian processes and erosion by slope winds coming off of the southern highlands and funneling through notches between massifs. In the Gusev region, surface materials of contrasting thermophysical properties have been interpreted as rocks or bedrock, duricrust, and dust deposits; these are consistent with a complex geological history dominated by volcanic and aeolian processes. At Meridiani Planum the many layers having different thermophysical and erosional properties suggest periodic deposition of differing sedimentological facies possibly related to clast size, grain orientation and packing, or mineralogy.

Thermophysical properties of the Isidis basin, Mars

[1] We investigated the thermal properties of the Isidis basin in order to understand the high values (>450 J m -2 K -1 s -1/2 ) located in the southern region of the basin. Thermal inertia data were compared to a variety of complementary data sets, including radar, visible, and results from mesoscale atmospheric simulations. We considered four mechanisms for creating the high thermal inertia, including (1) the thinning of a dust mantle, (2) the presence of unconsolidated, coarse-grained material, (3) high rock abundance, and (4) a high degree of induration. Induration is the scenario most consistent with the data, although we cannot rule out unconsolidated materials and it is likely that rocks contribute to values of thermal inertia to a lesser degree. We also investigated three mechanisms for controlling the geographical distribution of the high thermal inertia values, including (1) the influence of topography, (2) the role of surface morphology, and (3) present aeolian processes. Topography plays a significant role along the southern boundary of the basin but not within the basin itself. THEMIS data show a complex relationship between the thermal inertia and morphology. The wind patterns modeled by the Mars Regional Atmospheric Modeling System (MRAMS) are not fully consistent with the wind directions implied by streaks in the thermal data but are consistent with a second group of streaks observed in the visible data. This suggests that small-scale (tens of kilometers) streaks observed in the thermal data did not form under present-day, nominal winds.