A River Ran Through Mars

Well, it didn't take long for Curiosity to cross one major item off its Martian to-do list: find evidence of water. The search for water is part of NASA's ongoing quest to find life on other planets: if water means life on Earth, then water elsewhere means life elsewhere. Curiosity hasn't found liquid water, it's found evidence that liquid water once flowed on the surface. But for NASA, that's enough to suggest that life could have sprung up in this region of ancient Mars.

The proof came in pictures showing a jagged slab of rock. On this outcrop were a number of smaller rocks – Martian gravel as it were – about an inch in diameter that look not only to have been smoothed and rounded by running water but carried along from other locations as well. To the trained scientific eye, their shape is evidence that they were transported, and their size is evidence that they could only have been moved by water. Wind couldn't shape rocks the same way nor could it carry something that large.

The water-formed rocks were found in a large canyon where nearby channels were cut by flowing water, making up an alluvial fan. Water would have carried the gravel downslope before it formed a conglomerate rock that was likely covered before being exposed. From the size of gravel, mission scientists think the water was flowing pretty fast, about 3 feet per second, and suspect the depth to have been somewhere between ankle and hip deep.

All this, and the rocks haven't even been lasered yet. There hasn't been any contact science or chemical analysis of the rocks. Scientists have come to these conclusions based solely on the images returned from Curiosity. The next step will be contact science. After picking a good spot to drill into the rock, Curiosity will look for possible carbon deposits to determine whether the water in this region once supported life. Determining the age of the rocks will also be an important piece of the puzzle. Current estimates suggest these weathered rocks could be several billion years old.

It's definitely an exciting discovery from everyone's favorite nuclear powered roving chemistry lab, but amid all this excitement people seem to be forgetting that we've found evidence of water on Mare before.

Earlier this year, the European Space Agency announced it found evidence that water once existed on Mars based on orbital imaging. The ESA's Mars Express orbiter has been studying rocks blasted out of impact craters, a useful approach because impacts uncover material that was previously hidden beneath the surface. Along with NASA's Mars Reconnaissance Orbiter, Mars Express focused on Mars' ancient southern highlands and looked specifically at the chemistry of rocks embedded in the walls, rims, and central uplifts. It found 175 sites rich with minerals that can only be formed in the presence of water.

Scientists behind the mission suspect that underground water must have existed in Mars' southern region for a long time, long enough to alter the surrounding rocks' chemical composition. Of course, this is a different type of discovery than Curiosity's The nature of the rocks' exposure – ejecta from an impact – means there wasn't any evidence of water weathering the surface of these rocks.

But even before the ESA found chemical evidence of water on Mars, NASA's Phoenix lander returned images that suggested water exists as dry ice on the red planet's polar region. Dice-size crumbs of bright material showed up photographs of a trench the lander's scoop dug. There was some question about the nature of the material – something that bright and white could either be salt or ice. But scientists got an answer four days later when a second photograph showed the white material was gone. The change led mission scientists to conclude that the material was ice that sublimated (went from a solid state to a liquid one) after it's expose to the Martian environment. Salt can't disappear like that.

Further evidence for water came when Phoenix snapped self portraits that showed evidence of condensation on the lander's leg, beads that look like droplets of salty liquid water. Experts believe they were formed from a mix of water and dust that splashed up on to the lander when it touched down; the heat of the retrorockets could have melted any ice in the landers vicinity. Between disappearing ice and frozen mud droplets, the Phoenix team found enough physical and thermodynamical evidence to show that remnants of past water might be common on Mars.

Of course, these discoveries still leave us with speculation on whether there was life on Mars. Proving that the environment was right for life is half the battle. I for one am still hoping Curiosity finds some little fossilized bacteria. Now that will be amazing proof that life really existed on Mars.