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PSS Summer '13

Water from the Basement of Time

By Cynthia L. McVey

If one could have looked at Mars from space more than three billion years ago, it would have appeared as a pale blue dot, or a checkerboard of land with small bodies of water scattered around. Playing a large role in uncovering Mars’ mysterious metamorphosis into the Red Planet is John Grotzinger ’79, Sc.D. ’13, mission leader and project scientist for the Mars Science Laboratory.

The Curiosity rover—a self-contained science laboratory about the size of a Mini Cooper—was sent to Mars last year on a mission to find evidence that the planet could have supported microbial life. A little more than six months after it landed, it sent back evidence of a habitable environment.

“We first got a sense that we were headed in the right direction with the rover when we discovered an ancient streambed very early in the mission, after only a month of exploration,” explains Grotzinger. “We decided to follow the course of that ancient stream and it led us to an ancient lake—long since vanished—which preserved evidence of a formerly habitable environment.”

He explains the ancient water would have had abundant chemical nutrients and been relatively fresh, with low salinity and not acidic— drinkable by human standards.

“It’s very analogous to what would be a pond or shallow lake on Earth. The lake may have been ephemeral, meaning it might have dried up from time to time; we can’t tell for sure. But it was wet long enough to cause a series of chemical reactions that would have supported microbial life if it had ever originated on Mars,” he says.

Scientists have thought that water once flowed on Mars since Mariner 9 did a flyby of the planet in the late 1960s. The discovery of sedimentary rock on Mars in 2004 convinced them that not only did it flow, but it may have supported life.

“Sedimentary rocks very often form in the presence of water, usually by cementation of loose rock particles to form a rock. As this happens, the chemical composition of the water—and any organic materials in the sediment —can be trapped within the cementing minerals and preserved for billions of years,” explains Grotzinger. Ironically, it was conducting research on Seneca Lake as a student that led him to the career in which he’d discover Mars’ ancient lake.

“Thirty five years ago as a student at Hobart, I was cruising Lake Seneca and measuring the salt content of the sediment and water and trying to imagine how the lake became salty,” he says. “I had no way to know that someday I’d be asking the same question about a 3.5 billion year old lake on Mars. But in hindsight these experiences all merge into one that is bound by the study of waters, including those from the basement of time.”