The new data was collected by the NASA rover Opportunity in the Victoria impact crater, which is 750 meters across and 75 meters, in an equatorial region of the planet.
NASA's principal investigator for the rover mission, Steve Squyres, and his colleagues report in the journal Science that the sedimentary rocks analyzed by Opportunity contain sulfate salts and a mineral called jarosite - harsh chemicals that are also found in briny water here on Earth.
The rover found similar sulfur-rich chemicals in rock debris six kilometers north of the Victoria crater in the Meridiani Planum region of Mars where Opportunity first landed five years ago.
Squyres says the chemicals suggest the mineral deposits remained after ground water came to the surface of the crater floor and then seeped back into the ground.
He says that would mean water in all likelihood covered the landscape, helping to shape the topography of the entire region - not just one small piece of it.
"There's a region in which the rover landed that's pretty big; it's about as big as the state of Oklahoma. That's how large it is. And that's the area where we've been operating. And we've now found two places that are about six kilometers apart - four miles apart - that have this same pattern which makes us think that probably these salty, acidic conditions actually existed over that entire Oklahoma-sized region," he said.
Scientists involved in the Mars rover project have been hunting for signs of water because its presence would likely mean that life might have existed once on the Red Planet.
But Squyres says the sulfate salts and jarosite would have made for an extremely harsh environment. "I want to stress though that it was a nasty place. You know, we say water but this stuff was more like sulfuric acid. It was very, very salty; it was kind of a more like brine. These are conditions that some very hearty microbes on Earth can stand. But it would have posed a challenge for life I think. So it was a habitable world, but a tough one," he said.
Squyres says eroded, layered rock on the crater walls also suggests that water may have helped break down the rocks. When the water disappeared, this loose material would have been picked up by the Martian winds, forming the dunes seen widely on the Red Planet.
Steven Benner is an exobiologist and member of the Foundation for Applied Molecular Evolution, a group supporting the search for life on other planets.
Benner says the latest evidence that there was briny water on Mars, and the suggestion of a similarity to the ancient oceans on Earth, make it likely that life once existed on the Red Planet.
"We can see the evidence of those oceans in Victoria crater. They have minerals in them; the same kinds of minerals that are used by life on Earth. It's just that what happened on Mars was different on Earth. It's that Mars dried and lost its atmosphere, most of it, not all of it, whereas the Earth did not," he said.
But exobiologist Steven Benner says life forms on Earth and the life forms he believes also evolved on a watery Mars would have adapted very differently to their unique environments, meaning that if living organisms are ever found on Mars, they won't resemble anything on Earth.