Investigation of Anomalous Terrains on the West Flank of Olympus Mons using CRISM Data

The west flank of the Olympus Mons volcano hosts an anomalous linear chain of semicircular terrains. We report here analyses of these features using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and other instruments. The terrains appear bright in both daytime and nighttime data from the Thermal Emission Imaging Experiment (THEMIS) and have moderate thermal inertia, contrasting with the regional dust mantle. They have no observable topographic relief, and morphologically appear inconsistent with volcanic or sedimentary deposits. Several forms of aeolian activity are evident, including yardangs, dunes, and scour-like features. However, the yardangs and scours appear to predate the terrains, and superposed dunes, while ubiquitous, do not fully account for the spectral and morphologic properties. Targeted hyperspectral visible and near infrared data from CRISM (20-40 m/pixel, ~0.4 to 4 μm) of the terrains show distinct circumferential color zonation and internal banding. Differences in spectral slope and depth of the 3 μm water absorption are apparent within these color units. Relatively low albedo materials that comprise small dune fields are superposed on variably higher albedo areas. Both of these materials exhibit negative infrared spectral slopes, but it is most pronounced in the areas with highest albedo. Around the perimeter of the terrains are two albedo zones that appear transitional with the surrounding high albedo dust cover, progressively darkening inward. Along with the overall decrease in albedo, however, is an apparent increase in the depth of the 3 μm hydration band. Spectral features indicative of specific hydrated minerals (e.g, sulfates, phyllosilicates) have not been observed, but an enhanced 3 μm absorption could indicate that these anomalous terrains were influenced by ephemeral water at some point in the near past. Recent aqueous activity on the largest volcano on Mars may represent a unique opportunity for exploration of habitable environments. Location of the anomalous terrains west of Olympus Mons as observed in (A) THEMIS daytime infrared data with inset (B) showing CRISM coverage and location of (C) in red. (C) False color composite of CRISM image HRL0000CF8E (R=2.5, G=1.5, B=1.0μm) with white arrows pointing to areas with interesting spectral variability.