NASA's Mars rover Opportunityis parked by the shore of what used to be a salty martian sea, scientists reported today.
"We think Opportunityis now parked on what was once the shoreline of a salty sea on Mars," said Mr Steve Squyres, principal investigator for the science payload on Opportunityand its twin Mars exploration Rover, Spirit.
Scientists have long seen signs of liquid water on Mars, and the rovers' mission was to investigate areas believed to have been covered with water long ago. If there was water, theorists believe, there might have been life on the Red Planet, Earth's next-door neighbor.
This is the first time, though, that scientists have concrete evidence - new data from the rovers' analysis of the Mars rocks themselves - that water might have flowed on the martian surface.
"This dramatic confirmation of standing water in Mars' history builds on a progression of discoveries about that most Earthlike of alien planets," said Mr Ed Weiler, NASA associate administrator for space science.
"This result gives us impetus to expand our ambitious program of exploring Mars to learn whether microbes have ever lived there and, ultimately, whether we can," Mr Weiler said in a statement.
The Mars rovers can do more than take pictures and beam them back to Earth. They also carry three different scientific instruments that can analyze the composition of various rocks and a grinding tool that can drill down under the surface.
Opportunityhas been roving across the seemingly barren martian surface since January and is now working with rocks that were once covered with a rippling saltwater sea, the scientists said.
Opportunity'scontrollers plan to send it out across a plain toward a thicker exposure of rocks in the wall of a crater to see if they can find more evidence of standing water.
So far, scientists point to patterns in some finely layered rocks that indicate they were shaped by ripples of water at least 2 inches deep and possibly much deeper. This water was flowing at a speed of 4 to 20 inches per second, according to Mr John Grotzinger, a member of the rover's science team.
The patterns come in distinctive smile-shaped curves characteristic of water's impact on rock, rather than wind erosion, he said.
Opportunity'scurrent location might have been a salt flat when these rocks were forming, and might have been occasionally covered by shallow water and sometimes dry. On Earth, this type of environment can have water currents that produce the ripples seen in the Mars rocks.
The rover has also detected chlorine and bromine at the site, and the presence of these materials also suggests a martian salt flat that occasionally was underwater.
Scientists reckoned the rocks at the site had - at the very least - soaked in mineral-rich water, perhaps underground water, after they formed. But increased assurance that bromine was present strengthens the case for flowing water on Mars' surface.