The distribution, characteristics, and origins of rocky surfaces on Mars from remote thermal infrared observations.

摘要

Nighttime infrared spectral observations returned from the Thermal Emission Spectrometer (TES) are well-suited for determining the sub-pixel abundance of rocky material on the surface of Mars. The algorithm used here determines both the areal fraction of rocky material and the thermal inertia of the fine-grained non-rock component present on the surface. These thermophysical properties provide an important link between other physical measurements to interpret the nature of the materials present at the surface. Rock is defined as any surface material that has a thermal inertia ≥ 1250 J m-2K -1s-1/2. This material can be bedrock, boulders, indurated sediments, or a combination of these on a surface mixed with finer-grained materials. Over 4.9 million observations were compiled to produce the 8 pixels per degree (ppd) global rock abundance and fine-component inertia maps. Total coverage is ∼45% of the planet between latitudes -60 and 60. Less than 1% of the planet has rock abundances greater than 50%, and ∼7% of the mapped surface has greater than 30% rocks. Rocky regions on Mars correspond to the high inertia surfaces observed in thermal inertia datasets. The fine-component inertia is used to identify high inertia exposures that contain few rocks, and more homogeneous materials.; A major application of the rock abundance dataset is to determine the hazards to lander missions due to large rocks on the surface. For each of the candidate landing sites for the MER 2003 mission, the rock abundance and fine-component inertia have been mapped at 16 ppd. The most applicable datasets for determining rock hazards are presented, along with interpretations of the thermophysical characteristics from THEMIS day and nighttime thermal infrared mosaics. An analysis of all of the Mars landing sites and candidate sites has resulted in a means of classifying potential landing sites for applicability of surface rock modeling to determine the hazards to future landers.; The regions on Mars with the lowest thermal inertia, lowest rock abundance, and relatively high albedo represent a very fine-grained, poorly indurated, bright surface material. Where it occurs, the uppermost surface is variable in thickness throughout Tharsis, and may have experienced surface modification since deposition began. TES rock abundance, thermal inertia, and albedo have been used in combination to develop interpretations of the surface materials, with sensitivity from a few mum to centimeters into the subsurface. We have investigated isolated features in the Tharsis region that display relatively low ( 0.25) albedo and moderately high thermal inertia (150-400 J m -2K-1s-1/2), on the otherwise low inertia, high albedo surface. Using TES and THEMIS data to quantify surface characteristics and provide morphologic context, we have constrained the thickness of the mobile surface layer, and the thermal inertia of the underlying layer in the most prominent locations. Other regions in Tharsis have been identified that potentially have a mobile dust layer on top of equally bright surfaces, though without measurable changes in albedo. This suggests that the Tharsis low-inertia region is not experiencing uniform net dust accumulation.