TERRAIN ASSESSMENT IN GALE CRATER FROM SOL 0-500 USING ORBITAL THERMAL INERTIA AND IN SITU VISIBLE DATA

The ability to accurately assess surface terrain at the local scale is a crucial step in deconvolving geologic history, as well as providing important information about potential hazards that could endanger a roving vehicle during landing or traverse. We combine the results of orbital thermal inertia data with ground-based observations of rock abundance, and rock and soil characteristics along the Curiosity rover traverse. Our goals were to determine rock transport history, and improve our ability to assess current and predict upcoming terrain. Understanding terrain and its effects on hardware is a complex issue; here we describe a subset of geological observations that are related to it.

Curiosity traversed two geologic units up to sol 500: a Hummocky Plains Unit (HPU; sol 0-423) and a Rugged Unit (RU; sol 424->500). The lowest thermal inertia values recorded up to sol 500 occur in HPU terrain (~370). Terrain is characterized by cobbles in a range of shapes, though pyramidal sharp-edged pebbles (8-11 mm diameter, or small enough to fit between the wheel grousers) are uncommon. Bedrock is not visible, mantled by sandy material. This terrain appears to have caused the least amount of damage to the rover wheels. Morphology of the RU terrain is more variable with a relatively higher thermal inertia (~400). Between sol 424-452 and sol 471-500, there is variation in the presence and shape of pebbles and cobbles. Jagged to sub-jagged bedrock is also visible in some places, while in others bedrock and clasts are mantled with sandy material. Some damage to the wheels was recorded. In contrast, between sols 453-470, terrains display little sandy material, and are characterized by either a high abundance of pyramidal pebbles or the presence of jagged caprock, with some of the highest thermal inertias of this unit (~411). The greatest wheel damage was recorded within this range.

Higher thermal inertia values appear to be correlated with terrain that is potentially more damaging to Curiosity’s wheels. Results from in situ rock and soil assessment indicate that this correlation may be due to a combination of changing variables, all of which affect thermal inertia, and all of which are potentially correlated with wheel damage. These include a greater abundance of sharp, pyramidal pebbles, more exposed outcrop, and little cover by sandy material.