NASA announced Thursday that the Curiosity Mars rover has found proof that liquid water once existed on the Martian surface.
Water-worn gravel cemented in a conglomerate on rocky outcroppings must have been deposited by water, perhaps hip-deep and moving around three feet per second, say NASA scientists.
The rocks are too large to have been eroded and carried by the wind, so scientists are sure the culprit is water.
Scientists have named the outcropping "Hottah," after Hottah Lake in Canada.
"You had water transporting these gravels to the downslope of the fan," said NASA researchers to NPR. "The gravel then formed into a conglomerate rock, which was in turn likely covered before being exposed again."
The rocks are smooth and rounded, usually less than an inch in diameter.
"The shapes tell you they were transported and the sizes tell you they couldn't be transported by wind," said co-investigator Rebecca Williams. "They were transported by water flow."
This is not the first evidence of a wetter past for Mars. Orbiting satellites have spied canyons that look like they were dug out by erosion from large amounts of water. NASA picked the landing point for Curiosity because of the presence of what looked like an alluvial fan, silt and debris that spread out in a fan shape after being carried by a river.
"Before, we never really saw a rock on Mars where we could tell whether it was wind or water that was doing the transport," said Peter Doran at the University of Illinois, Chicago. "And now we have a clear sign of flowing water on Mars and we can get estimates of the size of the flow and so on. It's really fascinating."
The search for water on Mars is so intense because, as far as anyone knows, liquid water is required for life to form and flourish.
If life ever existed on Mars, it's likely any evidence of it will be found where there was flowing water. This is Curiosity's main purpose on Mars: to determine if the area surrounding its landing site was ever capable of supporting microbial life.
If life evolved independently on Mars, it makes it much more likely that life evolved elsewhere in the universe, strong evidence that we may not be the only sentient life in existence.
