SAN FRANCISCO, Dec. 13 (UPI) -- NASA's Spirit rover has found more evidence of water activity on Mars, scientists said Monday.
Spirit, which for the past several months has been exploring an elevated area near the Martian equator called the Columbia Hills, recently discovered rocks containing goethite.
"Our conclusion is that we have a mineral that forms only in the presence of water," said Goestar Klingelhoefer, lead scientist for Spirit's spectrometer, which analyzes the composition of the Martian rocks.
Since landing last January, both Spirit and its twin Opportunity have found evidence of the action of water on Mars. They also have found increasing signs that Mars may have gone through wet and dry periods during its 4 billion year history. Layers of rocks, one atop another, alternate between structures that appear windblown or sedimentary.
"We're definitely seeing rocks that have been altered by water," said Steve Squyres, chief scientist for the rover missions. He added, however, that the degree of alteration varies widely, indicating different conditions over time.
"It's a mess geologically," Squyres said.