A crater on Mars dubbed the Gusev Crater could have been "Lake Gusev" in the Red Planet's past, scientists say, containing a water lake that has appeared and disappeared more than once.
That's the conclusion of researchers at the Mars Space Flight Facility at Arizona State University who conducted an analysis of some old data from NASA's Mars rover Spirit that landed in the 100-mile-diameter crater in 2004.
Seen from orbit, the crater's rim appeared breached, as if a river channel had cut through it, but Spirit found the crater's floor was not lakebed-type sediments but rather volcanic rocks.
Rocks in some hills within the crater, called the Columbia Hills, showed evidence of being modified by water, but again, no sediments were found -- instead, they showed signs suggesting hydrothermal activity, likely from hot springs like ones found in Yellowstone National Park here on earth.
However, researcher Steve Ruff says there's hope for a Lake Gusev yet, thanks to another rock outcrop in the same hills.
The outcrop tagged Comanche, has high levels of magnesium-iron carbonate minerals, and the researchers say their analysis, published in the journal Geology, suggests an origin other than hydrothermal activity.
"We looked more closely at the composition and geologic setting of Comanche and nearby outcrops," Ruff says. "There's good evidence that low temperature surface waters introduced the carbonates into Comanche rather than hot water rising from deep down."
Comanche was formed as an ash deposit from explosive volcanic eruptions in or near Gusev, but as a lake within the crater filled and then dried, possibly numerous times, it infused Comanche and other rocks nearby with carbonates, Ruff says.
"The lake didn't have to be big," he says. "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."
The hills now exist as an island of more ancient territory surrounded by more recent lava deposits, Ruff says.
"Comanche and a neighbor outcrop called Algonquin are remnants of the older and much more widespread tephra (ash) deposit," he says. "The wind has eroded most of that deposit, also carrying away much of the evidence for an ancient lake."
The rover Spirit ceased operating in March of 2010, leaving the majority of the Columbia outcrops and additional Gusev targets unexamined.
In evaluating landing locations for another planned rover mission in 2020, NASA should give Gusev Crater serious thought, Ruff argues.
"Going back to Gusev would give us an opportunity for a second field season there, which any terrestrial geologist would understand," he says.
"Scientifically and operationally it makes sense to go to a place which we know has geologically diverse -- and astrobiologically interesting -- materials to sample."
"And we know exactly where to find them."
