NASA orbiter discovers evidence of liquid water on Mars

The Headline

NASA scientists have released photographs from the Mars Reconnaissance Orbiter (MRO) which they claim show evidence of liquid water on the surface of Mars. This is the first clear evidence that water can exist in its liquid state on Mars, though ice has been observed near the planet's poles and under the soil. Reservoirs of water might prove to be an invaluable resource to any future missions to Mars, and raise hopes among many scientists that life might have been able to develop and evolve in the extreme Martian environment.

The Science

The MRO is a probe that entered orbit around Mars in 2006. Since then it has observed the planet and sent thousands of photos back to Earth over the course of three Martian years (one Martian year is 1.88 Earth years).

During this time scientists have made many interesting discoveries, but one set of photos stood out (pictured below). It shows a region of bluffs and valleys which slowly develop dark finger-like features which extend down the slope during the spring and summer, fade in the winter, and return as the atmosphere heats up again. Puzzlingly the soil does not appear to darken because it is wet, but rather because grains of dust are disturbed and rearranged due to something flowing or moving downhill.

image credit: NASA/JPL-Caltech/Univ. of Arizona

“The best explanation for these observations so far is the flow of briny water,” said Alfred McEwen of the University of Arizona, Tucson. McEwen is the principal investigator for the orbiter’s High Resolution Imaging Science Experiment (HiRISE) and lead author of the paper about the flows, published in the journal Science.

Briny water is water that contains very high concentrations of dissolved salts, which are known to be prevalent on Mars' surface thanks to geological studies by the Spirit and Opportunity rovers. Briny water has a much lower freezing point than pure water, and is more viscous as well. This helps to explain how liquid water could exist on Mars, which features temperatures far below the freezing point of pure water.

Other qualities of the flows remain unexplained, for instance why no water or other volatile substances have been detected by the MRO's spectroscopy sensors. Scientists hypothesize that the water may evaporate into the atmosphere too quickly for the orbiter to detect, or that the flows may occur just under the surface of the soil. Another question is why the features disappear as the weather chills during the Martian winter.

“It’s a mystery now, but I think it’s a solvable mystery with further observations and laboratory experiments,” McEwen said.

The possibility of water on any interstellar body is an exciting one for scientists, but especially on Mars, our most accessible planetary neighbor. Life as we know it cannot exist without water, meaning both that it will be an important resource for any possible manned mission, but also that its presence vastly increases the hopes that indigenous life might be discovered on a planet other than our own.

The Bottom Line

The announcement by NASA expresses confidence that liquid water is responsible for the features observed on the Martian surface, but doesn't rule out the possibility of other geological mechanisms. In terms of its impact on a future manned mission, ice has already been discovered on Mars, so the existence of liquid water wouldn't make or break such an expedition. It does increase the interest in organizing such a venture for many scientists, as life is presumed to be much more likely in the presence of liquid water. At the very least the announcement highlights the vast amount that remains to be discovered in even the most familiar regions (relatively speaking) of our interstellar neighborhood.

http://www.nasa.gov/mission_pages/MRO/news/mro20110804.html - NASA mission news