Water is the elixir of life, and NASA scientists reported compelling evidence today that the tiny crater that the Mars rover Opportunity has been scooting around for the last month was once soaked in it.
“Liquid water once flowed through these rocks. It changed their texture, and it changed their chemistry,” Dr. Steve Squyres, a Cornell University astronomy professor and the principal investigator for the rover mission, said in a NASA statement. “We’ve been able to read the telltale clues the water left behind, giving us confidence in that conclusion.”
The finding greatly enhances prospects that Mars was a much more hospitable planet early in its history, possibly even amenable to the rise of life at one time.
The mission of the two rovers Opportunity and Spirit, which the space agency landed far apart on Mars in January, is to search for signs of water in the planet’s past. Scientists now believe that they have found just that in a small crater on the flat plains of Meridiani Planum, the landing site of the rover Opportunity.
Since its arrival there on Jan. 25, Opportunity has detected suggestive hints of past water — an iron mineral that usually forms in the presence of water — in bedrock that may be sediment that was deposited at the bottom of an ancient lake or sea. However, alternate explanations not involving water have also been possible: the layers of iron mineral could be volcanic ash or sediments carried by wind; the iron mineral can also form out of lava.
But in the last two weeks, close examination of the bedrock has provided evidence for the water theory so compelling that Dr. Squyres characterized some of it as a “slam dunk.”
“You can’t just come up with any other answer,” Dr. Squyres said in an interview before a NASA news conference today that announced the findings.
One indication of the significance that the scientists attach to their conclusion is the place they chose to announce it. Instead of briefing journalists at the Jet Propulsion Laboratory in Pasadena, Calif., where the mission is controlled, the scientists flew to Washington to hold a televised news conference in the more auspicious headquarters of the National Aeronautics and Space Administration.
“NASA launched the Mars Exploration Rover mission specifically to check whether at least one part of Mars ever had a persistently wet environment that could possibly have been hospitable to life,” said Dr. James Garvin, lead scientist for Mars and lunar exploration at NASA Headquarters in Washington. “Today we have strong evidence for an exciting answer: Yes.”
Gusev Crater and Meridiani Planum, the exploration sites for NASA’s twin rovers Spirit and Opportunity, are on opposite sides of Mars and are as different as New York City and the Illinois prairie. Gusev Crater is rocks, rocks everywhere. Meridiani Planum is flat, almost featureless, almost rockless and blanketed with a fine-grained red soil and dark pebbles.
Before the rovers landed, many scientists expected that the Spirit would land on more interesting terrain in Gusev Crater and that the Opportunity would have to drive quite a distance to find worthy objects of study.
By luck, the Opportunity overshot its target, ending in a shallow 72-foot-wide crater. The scientists gasped when the first photographs showed an outcrop of bedrock 25 feet away, the first piece of Martian bedrock they would be able to explore closely.
The bedrock contains fine layers, as thin as half an inch, indicating that it is sedimentary or layers of volcanic ash from eruptions. An instrument that measures thermal emissions identified in the dark pebbly surface an iron oxide that on Earth typically forms in the presence of water. The oxide probably gives the surface its dark color.
One intriguing feature of Opportunity’s crater is small pebbles, many almost perfectly round, scattered over the surface.
The statement from the Jet Propulsion Laboratory said that the key to the scientists’ findings announced today lay in the analysis of these pebbles, though the conclusions were not final.
“Round particles the size of BB’s are embedded in the outcrop,” the statement said. “From shape alone, these spherules might be formed from volcanic eruptions, from lofting of molten droplets by a meteor impact, or from accumulation of minerals coming out of solution inside a porous, water-soaked rock.
“Opportunity’s observations that the spherules are not concentrated at particular layers in the outcrop weigh against a volcanic or impact origin, but do not completely rule out those origins.”