June 04, 2010 -
The image left was taken by the panoramic camera on the Mars Rover Spirit shows the rock dubbed "Pot of Gold" (upper left), located near the base of the "Columbia Hills" in Gusev Crater. Scientists were intrigued by this unusual-looking, nodule-covered rock and investigated its detailed chemistry. To the right is a set of rocks referred to as "Rotten Rocks" for their resemblance to rotting loaves of bread.
The "Pot of Gold" rock outcrop that Spirit Mars Rover examined in late 2005 revealed high concentrations of carbonate, which originates in wet, near-neutral conditions, but dissolves in acid. The ancient water indicated by this find was not acidic; hence, it was favorable as a habitat for life.
"This is one of the most significant findings by the rovers," said Steve Squyres of Cornell University in Ithaca, N.Y. Squyres is principal investigator for the Mars twin rovers, Spirit and Opportunity, and a co-author of the new report. "A substantial carbonate deposit in a Mars outcrop tells us that conditions that could have been quite favorable for life were present at one time in that place."
Spirit inspected rock outcrops, striking a bonanza at one the NASA scientists named Comanche, along the rover's route from the top of Husband Hill to the vicinity of the Home Plate plateau. Magnesium iron carbonate makes up about one-fourth of the measured volume in Comanche. That is a tenfold higher concentration than any previously identified for carbonate in a Martian rock.
"We used detective work combining results from three spectrometers to lock this down," said Dick Morris, lead author of the report and a member of a rover science team at NASA's Johnson Space Center in Houston."The instruments gave us multiple, interlocking ways of confirming the magnesium iron carbonate, with a good handle on how much there is."
Massive carbonate deposits on Mars have been sought for years without much success. Numerous channels apparently carved by flows of liquid water on ancient Mars suggest the planet was formerly warmer, thanks to greenhouse warming from a thicker atmosphere than exists now. The ancient, dense Martian atmosphere was probably rich in carbon dioxide, because that gas makes up nearly all the modern, very thin atmosphere. It is important to determine where most of the carbon dioxide went. Some theorize it departed to space. Others hypothesize that it left the atmosphere by the mixing of carbondioxide with water under conditions that led to forming carbonate minerals. That possibility, plus finding small amounts of carbonate in meteorites that originated from Mars, led to expectations in the 1990s that carbonate would be abundant on Mars. However, mineral- mapping spectrometers on orbiters since then have found evidence of localized carbonate deposits in only one area, plus small amounts distributed globally in Martian dust.
"It was like looking through dirty glasses," said Steve Ruff of Arizona State University in Tempe, Ariz., another co-author of the report. "We could tell there was something very different about Comanche compared with other outcrops we had seen, but we couldn't tell what it was until we developed a correction method to account for the dust on the mirror."
Spirit's Alpha Particle X-ray Spectrometer instrument detected a high concentration of light elements, a group including carbon and oxygen, that helped quantify the carbonate content.
The rovers landed on Mars in January 2004 for missions originally planned to last three months. Spirit has been out of communication since March 22 and is in a low-power hibernation status during Martian winter. Opportunity is making steady progress toward a large crater, Endeavour, which is about 11 kilometers (7 miles) away.Casey Kazan via NASA