Water on Mars: Curiosity rover uncovers a flood of evidence

Water, water everywhere, and some of it fit to drink.

That's the picture of ancient Mars that has emerged during the past few months thanks to discoveries by NASA's Curiosity rover, which has been exploring the Red Planet since touching down inside Gale Crater in August 2012.

The announcements have come in dribs and drabs, but presented together recently here at the European Planetary Science Congress, they provide compelling evidence that Mars was quite wet in the distant past. [The Search for Water on Mars (Photos)]

During many sessions at the conference, which was held Sept. 8 to Sept. 13 in London, scientists presented details of the rover's most exciting finds, made before it began the long drive toward the towering Mount Sharp this past July.

And the words that could be heard most often were hydrogen, hydration, rocks and water. Especially water.

"We know that on Mars there was what we interpret to be a habitable environment , where water was good enough for us to drink," Melissa Rice, of the California Institute of Technology in Pasadena, said after a presentation on imaging results from Curiosity's workhorse Mastcam instrument.

She talked about rocks that Curiosity studied earlier this year, finding evidence that ancient Mars could have supported microbial life.

"We know that we had an initial habitable environment when these rocks formed, and then sometime later -- we don't know when -- these rocks had water flowing through them, through these fractures, leaving calcium sulfate behind," Rice said. "We don't know if that era would have also been habitable, but it tells us that there were at least two major wet stages."

Martian lakes?

One of the rocks Rice mentioned was a mudstone that Curiosity drilled into. Inside, researchers found clay minerals, which meant either formation in, or substantial alteration by, water on Mars.

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