Researchers have been on the fence as to whether or not "Lake Gusev" on Mars ever contained water, but a new analysis supports the idea that the region once held a lake.
The formation appears to be a lakebed surrounded by river channels, but a 2004 Spirit rover analysis of the 100-mile-wide "lakebed" determined it was actually made up of volcanic rock, as opposed to sediments consistent with the presence of lake water, an Arizona State University news release reported.
The nearby 300-foot-high Columbia Hills told a different story; rocks around the mountains did show evidence of having been altered by water. The scientists did not find lake sediments on these water-worn rocks, but noticed evidence of hydrothermal activity suggesting a phenomenon similar to the Yellowstone National Park hot springs.
A rock outcrop by the Columbia Hills, dubbed Comanche, is surprisingly rich in magnesium-iron carbonate minerals. A recent analysis provides new hope for the crater once holding a water lake.
"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," study leader Steve Ruff, associate research professor at Arizona State University's Mars Space Flight Facility in the School of Earth and Space Exploration, said in the news release.
Comanche is believed to be made up of volcanic ash (tephra) deposited by volcanic eruptions in the area. Floodwaters could have entered the lakebed through a nearby valley and remained for long enough to alter the tephra and cause a "briny solution," the news release reported. Once these brines evaporated they would have left behind carbonate minerals that could have gotten into Comanche.
"The lake didn't have to be big," Ruff said. "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."
"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 said.
The researchers hope that in the future a Mars rover will be able to revisit the puzzling crater.
"Going back to Gusev would give us an opportunity for a second field season there, which any terrestrial geologist would understand," Ruff said.
"Scientifically and operationally it makes sense to go to a place which we know has geologically diverse - and astrobiologically interesting - materials to sample," he said.
