Multispectral Properties of Fine-grained Materials at Gusev and Meridiani from MER/Pancam Observations

The Mars Exploration Rover Panoramic Camera (Pancam) instruments have acquired more than 41,000 and 37,000 multispectral images, respectively, from the rovers' landing sites and traverse paths within Gusev crater and Meridiani Planum as of early September 2005. The images have a resolution of from a few millimeters per pixel near the rover to a few meters per pixel for features near the horizon, and provide detailed information on the geology and morphology of the locations visited by the rovers. The 400 to 1000 nm spectral range of the color data also provides a limited amount of mineralogic information about iron-bearing phases, for selection of in situ analysis targets and comparison to and augmentation of more detailed compositional and mineralogic results from other rover instruments. These images include ten 360 degree panoramas acquired at Gusev and five 360 degree panoramas acquired at Meridiani. These panoramas were acquired using a subset of Pancam filters chosen to allow spectral parameterizations to be generated that provide maximal color unit discrimination within the available downlinked data volume and power constraints at the time of each observation. The images also include more than sixty limited color panoramas spanning at least 90 degrees of azimuth, and hundreds of 11-color multispectral spot observations of specific targets using all of the Pancam geology filters. Analysis of the large panoramas provides an assessment of the local-scale spectral diversity of each rover study site. Here we assess the nature of fine-grained materials at each site with results from the geographically-broad but spectrally-limited large panoramic color surveys, including the most recent data, augmented by much more narrowly-targeted full-color multispectral spot results. Fine-grained color units at Gusev include bright dust, bright and dark soils on planar surfaces (e.g., hollows) and in aeolian bedforms, dark dust created during Rock Abrasion Tool (RAT) grinding, and "white" subsurface soils in the Columbia Hills exposed by the rover wheels. Similar bright dust and dark soil units are seen at Meridiani, suggesting that they are a global unit. Other fine-grained units seen at Meridiani include several classes of the ubiquitous mm-scale spherules, mm- to sub-mm scale rock clasts, and bright dust generated by RAT grindings into the sulfur-rich sedimentary outcrop rocks.