The U.S. space agency NASA says Mars once had a shallow, salty sea that could have supported life. The evidence has come from chemical and physical traits of rocks being explored by one of the two robotic rovers on the red planet.
Mission scientists say instruments on the rover Opportunity have sensed sure signs in martian rocks that the planet had at least briny pools of water and possibly a more extensive salt water ocean.
"We believe that Opportunity is parked on what once was the shoreline of a salty sea," said Cornell University geologist Steven Squyres. He said the element bromium, a component of salt, is one clue in the rocks. Bromium is found in rocks formed in sea water on Earth. Another clue is that the layers of the martian rock are wavy, not flat and parallel to each other. This indicates that the sediments of material that formed them were washed along and deposited by ripples of water. "This was a shallow sea. These are salt flats. These are the kinds of environments that are very suitable for life. Now we don't know that life was there, but we have an environment that would have been suitable for life," he said.
When the scientists presented the first firm evidence of water on Mars three weeks ago, they could say only that the rock Opportunity explored was altered by water. But they left open the possibility that the rock was not formed by water in the first place. Now they are saying that the rock did form in water at least five centimeters deep and possibly deeper.
Photographs of the internal rock structure show that some layers lie at angles to the main layers. The scientists say that if the sediments had dropped into place after a volcano, for example, they would have fallen evenly, creating parallel layers.
A sediment expert at the U.S. Geological Survey who was not involved in the research, David Rubin, said pictures of the rock layers he has seen do not indicate that wind had deposited the sediments. "I was astonished. There on Mars were sedimentary structures just like we see on Earth. You can go out to your nearest beach or creek and take a shovel and dig in and see some of these same kinds of structures," he said.
Still unanswered, however, are how deep the Martian water was, how much area it covered, and how long it stood on what has since become a dry, barren planet. Next year, NASA plans to launch a satellite to orbit Mars with instruments to help answer the question of how extensive the salt water might have been.
NASA's chief of space science, Ed Weiler, said the new findings from Opportunity will influence where to send another U.S. rover mission later in the decade to retrieve soil and rock samples for return to Earth so scientists can probe them for microbial life. "If you have an interest in searching for fossils on Mars, this is the first place you want to go," he said.