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The search for life on Mars took a surprising downward turn yesterday. If life existed, it likely existed underground, reported Professor of Geological Sciences John Mustard in a study published in the journal Nature.

For the past five years, Mustard and lead author Bethany Ehlmann ScM'08 PhD'10 have been working with a group of scientists to determine how and where Martian clay was formed.

Their findings could help explain what the Red Planet looked like billions of years ago and where life would have had the best chance of thriving.

The presence of clay on Mars is significant in itself. Clay forms in wet environments, so its presence "is clear evidence that water stayed around long enough to do work,"  Mustard said. Clay formation also requires at least a moderate to high temperature — hinting at conditions suitable for life.

Yet an important question remained: Was this clay formed by water on Mars' surface or was it formed underground?

Many scientists thought the clay was formed in lakes on the surface of the planet. Evidence of lake basins and river deltas suggest that liquid surface water was once present.

But Mustard disagreed. "This wasn't where the action was," he said. Instead, much of the clay was formed in the planet's subsurface.

Light reflected from the planet allows researchers to infer the mineral composition of various clay deposits. From the composition of clay, scientists can learn a lot about where it was formed. Clay formed underground, exposed to higher temperatures and less hydrous conditions than at the surface, will contain different minerals than clay formed on the surface.

Satellites detected mineral compositions that pointed to underground formation processes. Much of the clay is located at the older and deeper portions of the Martian surface, further supporting Mustard's conclusion.

But the discovery goes far beyond the mineralogy of clays. Where there is water, there is life — or, at least, there could be.

The findings further indicate that there may be a greater chance life existed on the planet. Due to its protection from radiation and stability, the subsurface, Mustard explained, "is the more hospitable environment for life."

Before scientists will be able to venture into Mars' subsurface and search for life, the upcoming surface landing of the Mars rover —  which will actually be able to sample the chemical makeup of the clay — will test Mustard and his team's hypothesis.

Mustard explained that if a clay deposit has a more uniform composition, the deposit likely came from the same source and can be collectively used to infer where it was formed.

If the compositions are divergent, the clay could have come from many different sources, preventing scientists from determining where clay formation, and thus water and life-bearing conditions, primarily occurred in ancient Mars.


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