New evidence from Mars shows four layers of rock with different properties, helping to confirm long-held expectations that Mars experienced a series of environmental changes during active geological periods in its history. They may also point to underground water, one scientist says.
The data, collected by NASA's recently deployed Mars Odyssey spacecraft, is said by scientists to confirm less convincing data that had been returned by the Mars Global Surveyor, which has been orbiting Mars for several years.
"We knew from Mars Global Surveyor that Mars was layered, but these data from Odyssey are the first direct evidence that the physical properties of the layers are different," said Philip Christensen, principal investigator for Odyssey's camera system and a professor at Arizona State University. "It's evidence that the environment changed over time as these layers were laid down."
A mosaic of daytime infrared images of the layered Terra Meridiani region shows a complex geology with craters and eroded surfaces, exposing at least four distinct layers of rock. The image maps the temperatures of the features.
"When we look at these distinct layers we see that the temperatures are very different, indicating that there are significant differences in the physical properties of the rock layers," said Christensen, who presented his findings Wednesday at the spring meeting of the American Geophysical Union in Washington, D.C.
The temperature differences could be caused by the fundamental variations in either the size of the rock fragments in the layer, the mineral composition or the density of the layers.
Plausible explanations include a history of volcanic activity depositing layers of lava and volcanic ash; a history of different processes that created the layers through wind and water; or a history of climate change that varied the nature of the materials deposited.
Christensen thinks the layers are caused not by surface effects, but by changes in the planet's subsurface water table. The presence or absence of water and the minerals carried in it can significantly affect how sediment particles are cemented together.
With no clear evidence for surface water, precipitation or runoff, Christensen believes that changes in levels of underground water percolating through layers of buried sediments could account for differences in rock composition between layers. More complete infrared data, some of which has been collected by not analyzed, will help to confirm or disprove this and many other hypotheses concerning Mars' geology.
"I expect that the primitive geologic maps of Mars that we have constructed so far will all be redrawn based on Odyssey's new information," said Dr. R. Stephen Saunders, Odyssey's project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
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