The Mars rover Opportunity has discovered that potentially life-sustaining waters once soaked the surface of Mars, providing an answer to one of the most provocative questions of modern planetary science.
At a news conference Tuesday in Washington, NASA scientists said analysis of rock samples showed that salt-laden sediments were shaped by percolating or flowing water -- and may even have been formed by a great Martian sea.
"Opportunity has landed on an area of Mars where liquid water once drenched the surface," said Ed Weiler, NASA's associate administrator of space science. "This area would have been a good, habitable environment for some period of time."
He called the findings "a giant leap" toward determining whether life may have existed on Mars during a warmer and wetter time in the now-frigid planet's past.
Steve Squyres, a Cornell University geologist and chief scientist for the mission, said one of the key pieces of evidence was the discovery of dense deposits of sulfates -- similar to earthly Epsom salts -- in an outcropping of bedrock near Opportunity's landing site.
The mineral is typically left behind by receding groundwater or the evaporation of a salty lake or ocean.
Scientists used a grinding tool to look beneath the surface of the rock to be sure the salty deposits were more than a shallow crust. They then used an instrument called an alpha particle X-ray spectrometer, which can be used to shoot radioactive particles at mineral atoms to determine their mass and composition.
The rocks were found to be "full of sulfate salts," up to 40% of the total mass of the rocks, Squyres said -- "a telltale sign, we believe, of water."
Squyres said several other findings confirmed their assumptions.
The layered, scarred face of a rock scientists have been studying -- nicknamed El Capitan -- could have been shaped by wind or water. But a striated pattern called crossbedding included concave patterns typically caused by the crest lines of underwater ridges.
The rover's panoramic camera and microscopic imager captured a number of random, pockmark indentations, each a fraction of an inch long. The pattern typically forms when salt crystals grow within rocks sitting in briny water. When the crystals later dissolve or erode away, they leave holes like those seen on El Capitan.
