As Spirit struggled up the slope approaching the ridgeline, the rover's wheels churned up soil that grabbed scientists' attention. "This was an absolutely serendipitous discovery," said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the rovers' science instruments. "We said, 'My gosh, that soil looks very bright. Before we go away, we should at least take a taste."
The bright patch of disturbed soil, dubbed "Paso Robles," has the highest salt concentration of any rock or soil ever examined on Mars. Combined information gained from inspecting it with Spirit's three spectrometers and panoramic camera suggests its main ingredient is an iron sulfate salt with water molecules bound into the mineral. The soil patch is also rich in phosphorus, but not otherwise like a high-phosphorus rock, called "Wishstone," that Spirit examined in December. "We're still trying to work out what this means, but clearly, with this much salt around, water had a hand here," Squyres said.