Fresh observations of surface features known as recurring slope lineae (RSL) appear to have confirmed the presence of liquid water on Mars. The evidence of surface water may have profound implications in the ongoing search for Martian life, both ancient and present, and as a resource to be used in a future manned mission to the Red Planet.
Previous observations of RSLs, which were first discovered in 2010, drew many scientists to the theory that they may be the result of active water flows present on the Martian surface. The features appear as dark lines streaking down steep slopes such as Hale Crater. The running water theory was based on factors such as the RSLs' appearance at certain times of the year, with the streaks appearing to flow downhill during warmer seasons, where temperatures rise above -10 °F (-23 °C) , and subsequently fade in cooler periods.
However, though the observations were compelling, the scientific community lacked the evidence to conclusively point to water as the cause of the RSLs – that is, until today. New observations carried out by NASA's Mars Reconnaissance Orbiter (MRO) have provided strong evidence that the RSLs are indeed the result of seasonal water flows emanating from slopes present on the Red Planet.
The observations made use of the spacecraft's Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to sample the light absorption characteristics of the RSLs. NASA scientists then analyzed the readings back on Earth, and it was found that the absorption rates matched the characteristics of hydrated minerals called perchlorates. Based on the chemical signature returned by the MRO, it is believe that the flows are composed of a mixture of magnesium perchlorate, magnesium chlorate and sodium perchlorate.
"Our quest on Mars has been to 'follow the water,' in our search for life in the universe, and now we have convincing science that validates what we’ve long suspected," said John Grunsfeld, associate administrator of NASA’s Science Mission Directorate in Washington. "This is a significant development, as it appears to confirm that water – albeit briny – is flowing today on the surface of Mars."
An orthorectified image draped on a digital terrain model of the walls of Gale crater displaying clear examples of RSL
The chemical signature of hydrated salts was detected on a number of RSL points across the Martian globe, but only where the features were found to be very wide, with narrower RSL's exhibiting no traces of hydration.
"We found the hydrated salts only when the seasonal features were widest, which suggests that either the dark streaks themselves or a process that forms them is the source of the hydration" stated Lujendra Ojha of the Georgia Institute of Technology, Atlanta, and lead author of a report on the findings published on Sept. 28 by Nature Geoscience. "In either case, the detection of hydrated salts on these slopes means that water plays a vital role in the formation of these streaks."
The leading theory on how RSLs are formed revolves around a process known as deliquescence. This process describes the ability of perchlorate salts to absorb atmospheric water. When the humidity in the Martian atmosphere is high enough, the salts will absorb atmospheric water until they dissolve and create a liquid solution
Ordinarily, pure, unfrozen water would quickly boil off in to space, however the brine-like solution detected on the Martian surface would give the water enough stability to survive and flow downhill. The briny mixture detected in the RSLs should keep the water from freezing until it reaches below -94 °F (-70°C). In terms of quantity, the flows are predicted to be mostly subsurface, meaning that we could expect a thin layer of wet soil rather than actual flowing water.
Arguably the most exciting aspect of the announcement are the implications that the discovery has in regard to the existence of life on Mars, either now or in the ancient past. The presence of water on our planet was one of the key factors in the development of early life, and the discovery of this briny mixture on Mars means that the Red Planet may be much more conducive to near-surface microbial life. Most importantly, it has given future missions to the Red Planet an ideal target in the search for extraterrestrial life.
During the briefing, it was mooted that Curiosity may be sent to examine the flows, however the panel was unsure of whether the mobile laboratory had the ability to reach or carry out the necessary experiments. Furthermore there was a danger of contamination of microbial life from the rover itself. The panel outlined a scenario in which we make a breaking discovery, that turns out to be life that we brought with us in the first place.
There is also significant potential of using the newly-discovered water as a resource during future manned missions, for example as a source of oxygen and drinking water.
"All of the scientific discoveries that we are making on the surface of Mars, Curiosity at Gale Crater, observations from the Mars Reconaissance Orbiter are giving us a much better view that Mars has resources that are useful to future travelers" explained Grunsfeld. "When you have water, you have hydrogen and oxygen – that's what we make rocket fuel out of."
The ramifications of today's announcement will undoubtedly inform future efforts, both manned and unmanned seeking to explore and understand the Red Planet, especially regarding to Mankind's ongoing mission to discover extraterrestrial life. Mars is now a more attractive candidate than ever as a site to make this historic discovery, and serves as yet another incentive to extend manned exploration beyond low-Earth orbit.