A study of clays suggests they might have been formed in hot magma rich in water — too hot to support microbial life. A Caltech planetary geologist is coauthor.
A standing theory about water on Mars is linked to blueberry-shaped formations in the Martian soil, such as this one in an image captured by the rover Opportunity and released in 2004. An alternate theory published Sunday in the journal Nature Geoscience argues, however, that Martian water's source water would have been far too hot to support microbial life. (NASA/JPL/U.S. Geological Survey/AFP/Getty Images)
A new theory is pouring some cold — actually, some really hot — water on the idea that Mars could have been habitable in the past.
Planetary scientists searching the Red Planet for places that could have contained the building blocks for life look for clues in clays, which can offer some indication that water must have flowed on or just under Mars' surface. But a new study suggests that, at least in some cases, those clays might be a red herring.
A paper published online Sunday by the journal Nature Geoscience argues that such clays might have been formed in hot Martian magma rich in water. If so, that water would have been far too hot to support microbial life.
The argument stands in contrast to two more common theories, said study coauthor Bethany Ehlmann, a planetary geologist at Caltech. One of them is that liquid water flowing across the Martian surface would have interacted with surrounding minerals, forming the clays. In another scenario, underground water warmed by the planet's internal heat could have provided a comfortable living before it got bound up in the mineral structure of clays.
On Earth, clays are remarkably good at trapping organic material. So if organic compounds existed on Mars, clays would be a good place to find them.
If either of the prevailing theories about water is true, the Martian environment could have been hospitable for life, Ehlmann said. Superheated water and magma? Not so much.
"The clays would form as the lava cools from 1,500 degrees Celsius," she said. "That would not be a good habitat."
Ehlmann and her colleagues examined clay minerals similar to ones observed on Mars that were found in spots like Brazil and French Polynesia where water vapor escaping from the Earth's interior formed bubbles in the magma, which hardened into pockets of clay.
The light signatures of these Earthly clays are very similar to some Martian deposits. And some — but not all — Martian meteorites collected here on Earth appear to support the new theory, the study authors wrote.
It's possible that all three models could be right, depending on where you're looking, said Ralph Milliken, a planetary scientist at Brown University who was not involved in the study.
"It's certainly a different take on trying to explain the origin of some clay minerals on Mars," he said. "It does have some merit, and alternative hypotheses need to be considered fully."
But he said the story laid out in the new paper doesn't explain why the Martian surface appears to have tracks cut by flowing liquid. Nor does it account for blueberry-shaped mineral deposits of hematite that scientists believe may have formed when water ran past them.
The Mars rover Curiosity might shed some light on the debate by giving scientists a close-up look at some clays in the lower layers of Mount Sharp in the middle of Gale Crater. It is expected to arrive in about a year.