Scientists have discovered evidence sitting right under their noses that indicates there may have been more water on Mars than previously thought.
Back in 2005, a mineral-scouting instrument on the Spirit Mars Rover found Comanche, an outcrop of rock rich in carbonates in the Columbia Hills of Gusev Crater. But the data has only just been understood, because one of the instruments that detected the carbonate minerals was partly blinded by dust.
The Miniature Thermal Emission Spectrometer, or Mini-TES, was developed at Arizona State University.
"Mini-TES got dusted months before Spirit reached Comanche, and we didn't have a good way to correct for the dust effects at the time," says Steve Ruff, research scientist at ASU's Mars Space Flight Facility.
"We knew there was something weird about the outcrop's spectrum as seen by Mini-TES, but couldn't say what caused it."
What finally did the trick was developing a calibration to remove the spectral effects of the dust on the instrument.
"We're seeing a couple of large outcrops of rock poking through the soil of the Columbia Hills," says Ruff. "The rocks are about 25 percent carbonate by weight, by far the highest abundance we've seen on Mars."
Comanche and a neighboring small outcrop dubbed Comanche Spur have the same granular texture and Mini-TES spectral nature. Ruff says they are part of a stack of volcanic sedimentary rocks, draped over the underlying terrain.
NASA's other Mars rover, Opportunity, has discovered ample evidence for alteration of rocks by water in Meridiani Planum. But this was strongly acidic, making it unlikely that life could have start there. Finding outcrops of carbonate rock at Comanche shows that the hydrothermal water was liquid, chemically neutral, and abundant.
While there's no evidence for life, Ruff says, the conditions would have been more favorable for it.
A report appears in Science.