Source: NASA/JPL/Malin Space Science Systems

Because of a broken embargo, researchers from Malin Space Science Systems announced early a major discovery about the Red Planet at a press conference yesterday afternoon. The findings, which suggest that parts of Mars were once covered with lakes, will appear in this Friday's issue of Science. The results are based on a series of images taken by the Mars Orbiter Camera (MOC) of rocks dating from Mars' earliest days between 4.3 and 3.5 billion years ago. In these images, Michael Malin and Kenneth Edgett identify three types of outcrops on the planet's surface. All three varieties appear to be made of fine-grained materials deposited in horizontal layers--a characteristic trait of sedimentary rock. If there is life in the form of fossils anywhere on Mars, it would likely be found sandwiched between these rocks, as is the case here on Earth.

Although wind, volcanic activity and even cosmic impacts can deposit sediments, Malin and Edgett believe that those in the images MOC captured were most likely carried by water: many of the outcrops exist within basin-like features, which may have been lakes. "Some of the MOC images of these outcrops show hundreds and hundreds of identically thick layers, which is almost impossible to have without water," Malin says. Curiously, the researchers cannot tell where the sediments originated, nor how they were transported. They think that erosion may have wiped out both the sources of the sediments, and the gullies and streams by which they might have traveled.

Malin and Edgett do offer an alternative to the idea that water created these geological formations: perhaps fluctuations in the amount of solid carbon dioxide on Mars' surface brought on periods of high atmospheric pressure, increasing the atmosphere's ability to lift and move dust that was shaken loose during cratering events. But whatever the case, the presence of sedimentary rock on Mars makes the planet more complicated and more exciting to study, Edgett says. "This record is going to tell us a lot about what early Mars was like," he adds, "and maybe the early Earth as well, since we don't have a lot of rocks on our own planet from this time period."