A satellite orbiting Mars has found widespread deposits of clay - mineralogical evidence that very early in its history, the red planet was a watery place with broad lakes and flowing rivers.
While the findings provide no direct evidence that life ever thrived in those Martian waters, clay on Earth is very good at preserving traces of organic matter.
The deposits identified and mapped by a Maryland-built instrument aboard NASA's Mars Reconnaissance Orbiter are already influencing the selection of landing sites for the space agency's next Mars lander, which will search for evidence of past or present life.
"It's very exciting to me because it's [revealing] that Mars is a very diverse place. As we look at smaller and smaller scales, we see that all these different environments existed on different parts of the planet. It bodes well for life," said Bethany Ehlmann, a Brown University doctoral candidate who was the lead author on one of two recent papers on the discoveries.
Scientists reported the findings in today's edition of the journal Nature and in the June 2 issue of Nature Geoscience.
Among the instruments that revealed the broad distribution and diversity of the clay minerals was the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), developed at the Johns Hopkins University's Applied Physics Lab near Laurel.
The Mars orbiter began studying the surface mineralogy in November 2006. Its instruments have now mapped 60 percent of the planet and snapped 7,200 high-resolution images, according to APL's Scott L. Murchie, principal investigator for CRISM.
The Martian clays appear to have formed in the earliest, or Noachian, period of the planet's history, 4.6 billion to 3.8 billion years ago, as widespread water flushed through rocks and soil.
Some clay formed deep underground; other deposits formed in sands and river deposits on the surface.
CRISM found clay deposits across roughly half the planet's surface. Their chemical diversity suggests they formed in a wide variety of rocks, temperatures and other environmental conditions.
"The occurrences and diversity tell you the alterations by water were much more widespread during this period that was thought," Murchie said.
"It's a story of a Mars more pervasively wet than previously suspected during its earliest history."
Mars today is frigid and dry. Scientists interested in the question of life there, or the availability of water for future astronauts, have struggled to understand its early, more watery history.
