Curiosity finds ancient Mars habitable. Now, the bigger question.

The rock at left, seen by Opportunity rover on Mars, is formed from sulfate-rich sandstone, cemented in the presence of water, scientists say, but this environment likely was not habitable -- due to extreme salinity and acidity of the water. But the rock at right, seen by Curiosity, indicates an ancient habitable environment: neutral pH, chemical gradients that would have created energy for microbes, and a distinctly low salinity, which would have helped metabolism if microorganisms had ever been present. (NASA/JPL-Caltech/Cornell/MSSS)

NASA provided this Martian analog to the Yellowknife Bay area, where Curiosity has been exploring. At left, a pit exposing clay-bearing lake sediments, deposited in a basaltic basin in southern Australia. At right is a core sample from the lakebed, with layered, clay-rich sediments. The layers show the changing lake chemistry and environmental conditions over time. (NASA/JPL-Caltech/Ames)

Opportunity rover could only abrade the rock, left. Curiosity used its drill to bore the hole at right. (NASA/JPL-Caltech/Cornell/MSSS)

The result of the drilling was this scoop of powdered rock, which then provided proof that ancient Mars contained the ingredients for life. (NASA/JPL-Caltech/MSSS)

The Mars rover Curiosity has accomplished a primary mission objective in discovering that ancient Mars could have supported life.

Now, scientists wonder whether they can unearth the story of Mars’ transformation from a wet, possibly life-supporting planet to the red dust bowl it has become. What happened on Mars?

NASA scientists hope to find clues in Gale Crater. Unlike other parts of Mars, it has been found to have the properties that could have supported life on ancient Mars. The rock recently explored by Curiosity shows “neutral pH, chemical gradients that would have created energy for microbes and a distinctly low salinity, which would have helped metabolism if microorganisms had ever been present,” the space agency says.

Scientists were fortunate — and smart — in their choice of Gale Crater as a landing site. But Mt. Sharp was the main target.

“We first found evidence for an ancient river system in Gale Crater before we landed,” scientist Ashwin Vasavada told the Los Angeles Times in an interview Thursday. The landing site NASA chose was “within striking distance” of Mt. Sharp.

Instead of heading straight for Mt. Sharp “when we landed, we chose to drive 500 yards or so to check out the evidence” of the river system, “even though it was the wrong direction relative to the mountain.

“That choice has now paid off,” he said, “big time.”

Curiosity went on its historic drilling mission, which in turn led to analysis of powdered rock and the evidence it contained of the ingredients to life.

Now, “the team is even more excited to keep exploring,” Vasavada said.

Curiosity is set to climb Mt. Sharp’s foothills. And as Curiosity drives “through layers of rock laid down over millions of years,” researchers can look for clues to the planet’s history.

“With one habitable environment in the bag, we now can see if such environments persisted over time, and maybe even see Mars turn from an ancient, wet planet into the dry, barren planet it is today.”

– Amy Hubbard

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