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A larger composite image of Sojourner's first steps An image of surprising clarity. The rock directly to Sojourner's left was named "Barnacle Bill" and was the first to be analyzed by Sojourner's primary on-board analytical instrument, an alpha-proton X-ray spectrometer that is particularly adept at identifying and classifying the elemental makeup of material composed primarily of the lighter elements. From the pitted nature of the rock, Barnacle Bill is an igneous (lava-like) rock that cooled rapidly on the surface. The pits are almost certainly due to outgassing of volatiles dissolved in the rock before it reached the surface of Mars.
The last prevailing wind direction in this photograph was right to left. A fine silt creates wind drifts, much like snow drifts, trailing the left side of each major barrier to a generally laminar flow across the surface. Similarly, the areas directly in and on the front of the rocks are scrubbed clean of small-grained particles due to the overpressure wave that develops in what was presumably a rather constant air flow. This fine sand-and-wind pattern is similarly common on deserts here on Earth. |