A crater larger than Phoenix, a channel that is hundreds of miles long and a thin atmosphere—these are all qualities scientists have observed on Mars, specifically in the Gusev Crater region. But a new discovery aided by an ASU professor suggests another transforming element: traces of an ancient lake.
The search for evidence of life on Mars has taken a new step, thanks to Steve Ruff, an associate research professor in the School of Earth and Space Exploration, and his team. Their work, which proves the ancient existence of water in Mars’s Gusev Crater, was published in the April 2014 issue of the journal Geology.
The investigation began in 2004, when the Mars rover Spirit landed inside the crater in search of an ancient lakebed. The area seemed promising, with a channel leading to the crater that appeared to have carried water.
But Ruff said there was early disappointment from Spirit.
“From day one, it was apparent that we hadn't landed on an ancient lakebed,” he said. “One thing we were looking for was layered sedimentary rocks that may have settled in an ancient lake, (because) on Earth, you can find these sediments after a lake dries up. We looked and never really found them.”
Even when the rover traveled to the nearby Columbia Hills and found carbonates, minerals that suggest the existence of water, scientists assumed the minerals came from volcanic activity instead because the makeup of the crater’s floor was volcanic rock.
But Ruff and his team re-evaluated the carbonates and found they suggested something very different.
“People were hoping for thick sedimentary layers from a long-standing lake that some people believe may have filled the crater,” he said. “But we may be seeing the last staves of the lake, or it was never this beautiful filled-up crater. … So if this channel was carrying flood waters, and it filled up at least partially the crater and dried up, you would see evidence of that in the minerals, and that’s what the carbonates are.”
Ruff said the carbonates show the existence of smaller, temporary lakes and ponds, called playa lakes, that would only fill the lowest portions of the crater when floods occurred. These floods could have come from a variety of sources, including strange events that don’t happen on Earth, he said.
“Mars is mysterious in that it forms floods out of nowhere,” Ruff said. “Literally there are places on Mars where the ground seems to break apart and floodwaters emerge fully formed, called a catastrophic outflow.”
Although the Gusev Crater has a channel that could suggest catastrophic outflow, Ruff said the characteristics of the channel make traditional precipitation much more likely.
“(The channel) shows a network of valleys going into it,” he said. “They may have formed from rainwater or melting snow, for example. People are reluctant to talk about precipitation on Mars, because the climate is so dry now … so you have to look to a climate early in Mars’s history that was probably very different.”
This discovery not only changes the way scientists will view the Gusev Crater but also furthers NASA’s search for life, Ruff said.
“Finding lakes on Mars is all about the possibility of habitable environments,” he said. “NASA is interested in looking for habitable environments on Mars because of the possibility that life may have been there. … So the theme here is the search for life. And the search for water is a proxy; it’s a pathway to the search for life.”
Ruff said with this discovery, he believes evidence of microbial life is likely to appear at some point, which would revolutionize the idea that Earth is the only planet that can support life.
“The reason this is such a big deal is because right now we only have one example of life in the universe, on this planet,” he said. “So even if we just find microbial life on Mars we can add another planet. … It seems crazy that there's only one example of life in the universe.”
Jack Farmer, who teaches geological sciences in the School of Earth and Space Exploration, said Ruff’s team’s work is likely to have a large impact on the scientific community.
“We are able to see into the past a little bit, into a part of the Gusev history that is largely buried in other places, and we can see that there might have been a lake and look at other ideas that have been corroborated over time,” he said.
Farmer said the discovery shows the lasting impact of Spirit’s mission on Mars.
“This discovery comes from mining the data that came through a long time ago, so there is still room for discovery even though we’re not exploring Mars right now,” he said. “Spirit, may it rest in peace because it stopped operating a couple years ago, it still has a living legacy of discovery, which is pretty impressive.”
Similarly, Fabrizio Alfano, a postdoctorate researcher who collaborated with Ruff on the discovery, said he is proud of his work with Ruff and its potential for the future of Mars exploration.
“It was a very difficult collaboration, but I think we produced really nice results,” he said. “It was quite an exciting and challenging collaboration with him.”
Ruff said because the evidence of ancient lakes in Gusev has been proven, he plans to advocate for Gusev as a landing site for the next Mars rover, which will be launched in 2020. The selection of a site is competitive, with scientists competing from all over the nation, he said.
Until then, he said he is excited and proud of his team’s work because they resurrected an idea that most scientists had abandoned.
“It’s exciting for me to contribute this new perspective and bring back the use of the ‘L’ word,” he said. “We can talk about a lake in Gusev because we have strong evidence now for that ancient lake. Before this new work, it was not apparent that we had found what we went looking for.”
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