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What Pathfinder Found: Some Highlights
The Sojourner rover approached a variety of rocks strewn around the Lander and examined them with an instrument called APXS (for alpha proton X-ray spectrometer) designed to measure elemental composition of materials. The results suggest that one crusty looking rock, which the mission controllers dubbed "Barnacle Bill", is rich in a light-weight quartz-rich type of volcanic rock called andesite. This finding suggests that Mars was once thermally active and able to melt and differentiate rocks. (When a large mass of deeply buried rock melts on the Earth, the heavier components sink to the bottom and the lighter ones rise to the top, due to bouyancy; this separation by density is called differentiation.) "Barnacle Bill" appears to be more differentiated than the martian meteorites found on Earth.
The magnetic materials experiment shows dust collecting through time on magnets attached to the Lander. All the Martian dust appears to be at least slightly magnetic. The dust is thought to contain maghemite, a magnetic mineral formed in environments of scarce oxygen.
The Pathfinders meteorological instruments detected the passage of a "dust devil" on sol 25 (the 25th Martian day after landing). Extensive water-ice clouds have been photographed in the pre-dawn hours by the Lander camera. Dune-like features and wind shadows extending from rocks have been identified in other images.
More details on scientific results from Pathfinder can be found in a link from the National Space Science Data Center.
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