Rock abundance on Mars from the Thermal Emission Spectrometer

Nighttime infrared spectral observations returned from the Mars Global Surveyor Thermal Emission Spectrometer (TES) are well suited for determining the subpixel abundance of rocks 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 nonrock component present on the surface. Rock is defined as any surface material that has a thermal inertia ≥1250 J m^-2 K^-1 s^-1/2. This 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 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 primarily to the high-inertia surfaces observed in thermal inertia data sets. The fine-component inertia data set is used to identify high-inertia exposures that contain few rocks and more homogeneous materials.