April 10, 2014
Old Spirit Data Points To New Evidence Of Ancient Water In Mars Crater
Lawrence LeBlond for redOrbit.com - Your Universe Online
The hunt for a confirmed source of ancient water on the Red Planet may be over (or just beginning), at least for one group of scientists. Mars scientists looking at old data provided by NASA’s Spirit, one of the two rovers that landed on the Martian landscape a decade ago, have found evidence of ancient water inside the crater in which the rover landed.
Spirit landed in the 100-mile-wide Gusev Crater in 2004 and scientists have since been trying to determine if the crater itself was home to a body of water. Steve Ruff, an associate professor at Arizona State University’s Mars Space Flight Facility in the School of Earth and Space Exploration, believes the crater did hold an ancient lake that may have “come and gone” more than once.
In a report published in the April 2014 issue of the journal Geology, Ruff and his colleagues say the Gusev Crater is the perfect candidate for searching for evidence of ancient water. When viewed from orbit, Gusev, with its southern rim breached by a meandering river channel, looks like it once held a lake. One of the main mission directives for Spirit was studying the rocks within the crater, yet scientists were scratching their heads when instead of lakebed sediments, they found volcanic rock.
Strangely enough, 300-foot-high Columbia Hills, which sat less than two miles away, was found to contain evidence of ancient water. Upon arriving at the site, Spirit discovered that the ancient rocks there had been altered by water, despite the fact that no lake sediments had been found at this site either. What they did find was evidence of hydrothermal activity – similar to the hot springs of Yellowstone here on Earth.
But this evidence of hydrothermal activity didn’t stick, according to a later analysis by Ruff and his colleagues. In 2010, Ruff worked with a team to uncover a source of unusually rich magnesium-iron carbonate minerals in the Columbia Hills rock outcrop, which has become known as Comanche. While the carbonate minerals were originally attributed to hydrothermal activity, the new analysis points to an entirely different origin.
"We looked more closely at the composition and geologic setting of Comanche and nearby outcrops. There's good evidence that low temperature surface waters introduced the carbonates into Comanche rather than hot water rising from deep down," Ruff said in a statement.
Scientists say Comanche started out as a volcanic ash deposit known as tephra that originally covered Columbia Hills and the adjacent plains. This material came from explosive eruptions somewhere within or around Gusev, explained Ruff.
Eventually, the crater was filled with flood waters from the huge valley that breaches the crater’s southern rim. These floods appear to have ponded long enough to alter the tephra, producing briny solutions. Once the brine evaporated, carbonate minerals were left behind. As the lake filled and dried, perhaps many times throughout history, it loaded Comanche and its neighboring rocks with these carbonates.
"The lake didn't have to be big," Ruff noted. "The Columbia Hills stand 300 feet high, but they're in the lowest part of Gusev. So a deep, crater-spanning lake wasn't needed."
As seen today, the Columbia Hills rise as an island of older terrain surrounded by younger lave flows, explained Ruff.
“Comanche and a neighbor outcrop called Algonquin are remnants of the older and much more widespread tephra deposit. The wind has eroded most of that deposit, also carrying away much of the evidence for an ancient lake,” he added.
Spirit, which has given scientists a boatload of data to work with, fell silent in March 2010 and has not been heard from since. Still, most of Gusev Crater and Comanche has gone unexplored and Ruff would like to see that area targeted by future rovers currently being developed at NASA.
NASA is evaluating landing sites for its newest sample-collecting rover, which will launch in 2020, and Ruff said Gusev deserves serious consideration.
"Going back to Gusev would give us an opportunity for a second field season there, which any terrestrial geologist would understand," argued Ruff. "After the first field season with Spirit, we now have a bunch more questions and new hypotheses that can be addressed by going back."
The Mars rover 2020 mission will be an historical one because it will be the first to be able to collect and cache samples of the Martian surface with the hopes of being able to return to Earth. Ruff maintained it would make going back to an already visited site that much more important.
"Scientifically and operationally it makes sense to go to a place which we know has geologically diverse – and astrobiologically interesting – materials to sample," Ruff said. "And we know exactly where to find them."