US: Flowing water once lapped the shoreline of a long-dead saltwater sea, not in Earth's distant past but on Mars.
New evidence recovered by the Opportunity rover provides yet more evidence of past liquid water on the Red Planet's surface.
NASA's Opportunity rover continues to ramble across the bottom of a crater on Mars, searching for more proof of a wet - and possibly biological - history. Yesterday, the agency released yet more indications of water on Mars.
"We think Opportunity is parked on what was once the shoreline of a salty sea on Mars," Dr Steve Squyres of Cornell University stated yesterday in Washington.
Researchers found evidence of "bedding patterns" in finely layered rocks, "shaped into ripples by water at least five cm deep, possibly much deeper, and flowing at a speed of 10 to 15 cm per second," added Dr John Grotzinger of MIT in Boston.
"Ripples that formed in wind look different than ripples formed in water," he stated. The findings point towards a shallow salt-flat similar to those found on Earth, at the edge of oceans or in desert basins.
The telltale patterns, called "crossbedding" and "festooning", shift loose particles into characteristic ripples - shapes that, over millions of years, hardened into the rock layers being explored by Opportunity.
The rover also found evidence of chlorine and bromine in the rocks, suggestive of this kind of salt-water environment.
If this is so, and if these basins harboured past life, the rock-type serves as an ideal repository, according to Dr Squyers.
"The particular type of rock Opportunity is finding, with evaporite sediments from standing water, offers excellent capability for preserving evidence of any biochemical or biological material that may have been in the water," he stated.