Cold Hard Truth

New study reveals that possible life on Mars would be located deeper than previously thought

New findings from a team of scientists including Surdas Mohit of Scripps Institution of Oceanography at UC San Diego, suggest that any liquid water that might exist below the surface of Mars, and any possible organisms living in that water, would be located deeper than scientists had suspected.

The first detailed view of the northern polar cap of Mars reveals that the crust and upper mantle of Mars are stiffer and colder than previously thought.

The discovery was made using the Shallow Radar instrument on NASA's Mars Reconnaissance Orbiter spacecraft, which has provided the most detailed pictures to date of the interior layers of ice, sand and dust that make up the north polar cap on Mars. The radar images reveal long, continuous layers stretching up to 1,000 kilometers (600 miles), or about one-fifth the length of the United States. The results were published in the May 25 issue of Science Express, the early online edition of the journal Science.

"One of the major discoveries is that the base of the ice cap is very flat," said Mohit, the paper's co-author and postdoctoral researcher at Scripps. "This challenges our understanding of the composition of Mars and the concentration of radioactive elements in the mantle, which are an important heat source over geologic time."

Report lead author Roger Phillips of the Southwest Research Institute in Boulder, Colo., said the team discovered that the rocky surface of Mars is, tellingly, not bending under the load of the north polar ice cap.

"This implies that the planet's interior is more rigid, and thus colder, than we thought before," he said.

Mohit modeled the response of the planet to the load using a variety of existing models of the thermal structure of Mars and how it changes over time. All of the models resulted in substantially more bending over the ice load, similar to a bookcase buckling under a heavy load of books, than observed over a fraction of the time that the cap is believed to have existed. Therefore, the mantle is colder and must contain a lower concentration of these radioactive elements.

On Earth, the weight of a similar stack of ice would cause the planet's surface to sag. The discovery of a thicker Martian outer shell implies that any liquid water lurking in aquifers below the surface would have to be deeper than previously calculated, in places where temperatures are warmer.

—Annie Reisewitz

June 2008