Other
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusm.u44a..02w&link_type=abstract
American Geophysical Union, Spring Meeting 2004, abstract #U44A-02
Other
5464 Remote Sensing, 5470 Surface Materials And Properties, 6225 Mars
Scientific paper
We have used the Pancam and Microscopic Imager on the Opportunity rover at Meridiani Planum to understand the soil characteristics within the 20 m diameter crater where the rover landed. The majority of the soils consist of a well sorted lag deposit composed of millimeter-size grains of multiple sources superimposed on a finer soil matrix. The millimeter-size grains vary in size and morphology across the crater floor, with the largest (2-10 mm diameter) and most spherical grains adjacent to the layered outcrop, and smaller, more irregular sizes moving away from the outcrop towards the center of the crater. The soil right next to the lander is mostly composed of very fine grains (avg. 150 microns) with larger grains between 1 and 2 mm in diameter. Adjacent to the outcrop, the soils are dominated by spherules that have weathered out intact from the layered outcrop. It's likely that some of the non-spherule millimeter grains represent outcrop material that has been weathered to finer particle sizes and subsequently mixed into the soil. Underlying the spherules is a darker, finer soil that is spectrally similar to the soils near the lander. Undisturbed hematite-poor and hematite-rich soils, as determined by the Mini-TES instrument, show no significant differences in grain shapes or sizes. Rover wheel tracks show that the spherules and millimeter-size grains have been pushed down into the finer soil by the movement of the rover, but they have not been crushed. A similar effect was seen both from the Mossbauer contact plate after it was pushed into the soil, and also in the airbag bounce marks where the larger spherules have disappeared within the bounce marks, most likely due to burial, and there is a corresponding lower hematite signature. A 10 cm deep trench dug by a rover wheel reveals a brighter substrate on the trench floor, and a bumpy texture of soil with embedded shiny spherules in the upper wall. The brighter trench floor may be a photometric effect from the compaction rather than a distinct soil type. Linear ripples spaced 5-8 cm apart are concentrated adjacent to the lander and near the center of the crater. The ripples lack the millimeter-size grains visible throughout the crater floor. Intra-ripple soil within the larger ripples contains patches of brighter material that is spectrally distinct from all other soils and rocks thus far analyzed by Pancam, including the layered outcrop. Based upon orbital images of the landing site, the crater floor has a lower albedo than the terrain outside the crater. Consequently, the soils we have analyzed thus far inside the crater may either contain a higher percentage of darker grains or they may not be representative of the soils covering the plains of Meridiani Planum.
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