Adding a complication to the search for life on Mars, new surface maps reveal that the history of the red planet may have been cool and dry, according to Denver-based scientists at the U.S. Geological Survey.
By using an instrument aboard the spacecraft that orbits Mars, scientists can take thermal "pictures" that reveal the types of minerals on the planet surface.
Scientists Roger Clark and Tom Hoefen completed 500 trillion calculations to combine all the data from the survey into surface maps that cover 75 percent of the planet. From the maps, they discovered large expanses of olivine - known to change into another mineral in the presence of liquid water.
Their discovery contradicts former theories that Mars was warm and wet in its past - the olivine would not be present on the planet's surface if water had run over it or had rained on it.
Clark presented the discovery at the annual meeting of American Astronomical Society Division of Planetary Sciences in Pasadena, Calif., on Friday. Clark and Hoefen could not be reached for comment after the presentation.
"We just wouldn't see olivine in a wet, moist environment," said Gregg Swayze, a geophysicist at the survey. "There are no clays or carbonates or limestone on Mars either. You would expect clays and these other things if liquid water was on it at some point."
Swayze, who did not participate in his colleagues' research, said the valleys on Mars, thought by some to have been carved by rivers, were more likely created by flows of cold liquid and gas carbon dioxide carrying debris. The flow would be similar to that of a glacier, but very fast.
When Swayze passed along a study explaining this theory to Clark and Hoefen, "it just clicked," Swayze said. That paper was recently published in the scientific journal, Icarus, by an Australian scientist.
However, the surface maps also revealed a mineral usually present around water: coarse-grained hematite, the origin of which is still unknown. On Earth, hematite is often found in a hot spring or lake bed.
So Clark and Hoefen's discovery does not mean life won't be found on Mars, CU geological sciences professor Bruce Jakosky is quick to point out.
"In terms of understanding the geological history, this discovery is important," said Jakosky, director of the Center for Astrobiology at the University of Colorado. "But in my mind it doesn't change anything as far as the potential for Mars to hold life."
Jakosky added that Mars meets all of the environmental conditions for life, such as the presence of chemical elements that construct life and sources of energy.
And even with his new information, Clark concurs with other researchers that frozen water probably exists under the surface. The data used in Clark and Hoefen's study come from only a very thin top layer of the surface.
There is still only one way to know for sure if life exists on the red planet, Jakosky said.
"We have to go there," he said. "We are not going to find it here on Earth."
"You can't conclude that the prospects of finding life are gone now," he said. "This just adds a complication."