While NASA’s manned space program remains in crisis, its unmanned attempts at exploration, especially on Mars, keep chalking up successes. Using infrared cameras aboard the MarsGlobalSurveyor and MarsOdyssey spacecraft, planetary geologist Philip Christensen of Arizona State University and his colleagues are finding detailed signs of life—geologic life, at least—on the Red Planet.
Top, bottom: Courtesy of NASA/JPL/ASU/
Philip Christensen; middle, courtesy Los Alamos
Water on Mars leaves many kinds of traces. Gullies along the rim of this 11-mile-wide crater may have formed by water coursing out from the bottom of snow deposits (top). A plot of hydrogen (middle) traces the locations of ice in the soil, while a map of hematite (bottom) shows where water has altered surface minerals. In both maps, red denotes the highest concentrations of water.
When the sun heats the Martian surface, each type of rock radiates back a unique pattern of infrared wavelengths. Taken at different points across the floor of a volcanic region called Nili Patera, the images show areas of exposed bedrock, probably scoured by sand erosion. In Ganges Chasma, a huge canyon, stretches of pristine olivine-rich basalt imply that the surface has been little altered by water. But a few areas, such as Terra Meridiani, contain hematite, a mineral that usually forms in the presence of water. Christensen says that deep hydrothermal processes could have created the hematite, which was then exposed by weathering. So far, however, the infrared cameras show no indication of current geothermal activity. Most recently, he has discovered that Mars is coated with carbonate-rich dust, possibly a relic of a thick, heat-trapping carbon dioxide atmosphere that blanketed the planet eons ago.
Christensen also sees possible signs of snow deposits on Mars, which might have melted and carved out the sinuous gullies spotted earlier by the GlobalSurveyor’s optical camera.
Meanwhile, a team at Los Alamos National Laboratory has used another Odyssey instrument to reveal that subsurface ice seems to be distributed widely across the Martian surface. “We are discovering that Mars has a great deal of water frozen in snow and ice and that it may have many of the processes and landforms we see in the Arctic regions of Earth,” Christensen says. The big question is whether that water ever formed lakes or ponds where life could have taken root. NASA’s twin MarsExplorationRovers and the European MarsExpress mission will arrive in the next two months to help find out.