So Liquid Water Flows on Mars -- Now What?
The discovery of seasonal water flows on the surface of Mars could galvanize both the search for indigenous life as well plans for future human settlements, but don’t pack your bags quite yet.
The discovery of seasonal water flows on the surface of Mars could galvanize both the search for indigenous life as well plans for future human settlements, but don't pack your bags quite yet.
For the immediate future, NASA's Mars Reconnaissance Orbiter, which provided the legwork that led to Monday's announcement, will continue to gather high-resolution images and chemical data from areas, known as recurring slope lineae, or RSL, that have been linked to recent briny water flows.
These dark, narrow streaks cut into cliff walls throughout the planet's equator are unreachable by Curiosity and Opportunity, the two rovers now operating on Mars, and the Curiosity-class rover that is due to launch in 2020.
"Curiosity has gone up some pretty steep slopes, but some of these briny features are in tough terrain. It'd be trivial to an astronaut in a spacesuit to go up and investigate, but it's very hard for a rover, so we're a little ways off," said John Grunsfeld, NASA's associate administrator for science.
"I think (the discovery) will really drive the ingenuity of our scientists and engineers to come up with a viable experiment – and hopefully we can do it in the 2020s -- that would go and investigate these areas and perhaps even return samples from these areas some day," he added.
The existence of regions associated with present day water also means that visiting rovers must be properly sterilized to assure that hitchhiking Earth microbes don't contaminate potential native populations.
"We're being very careful that we don't send a spacecraft to Mars with the intention of detecting Martian life and find out that we've detected the Earth life that we took with us," Grunsfeld said.
Curiosity, which has provided evidence that ancient Mars had the necessary ingredients and suitable environments for microbial life, could end up playing a role in the search for present-day water as well.
Scientists have noticed RSL-like streaks in the walls of Mount Sharp, the three-mile high mound rising from the floor of Gale Crater, which Curiosity has been exploring since August 2012.
"We don't really know if Curiosity will have an opportunity to go to one of these areas and make measurements," said NASA's planetary science chief Jim Green. "They may or may not be RSLs. We've got a lot of work to do on that."
After three years of intense radiation exposure on Mars, Curiosity could be sterile enough to venture near a potential RSL, but its suite of instruments might not be suited for the job, Green added.
"It has a limited set of capabilities to be able to make any sort of detection in this area," he said.
Scientists would like more information on where and when RSLs form. Mars Reconnaissance Orbiter, which has been operating for nearly nine years, makes its observations at 3 p.m. Mars time, the hottest part of the day. Scientists had expected that any trace of water on the surface would have evaporated by then.
The realization that some telltale chemical footprints of water linger into the afternoon has scientists wondering what they might discover with an orbiter that makes observations in the cooler mornings.
"Right now, these RSLS are only known to exist on very steep, rocky slopes -- places where we can't land directly," planetary scientist Alfred McEwen, with the University of Arizona, told Discovery News.
"There may be water ... on flat areas as well that we just don't know about. Maybe we can find this in locations that are more accessible," he said.
Another recent theory suggests these gullies may have been caused by dry ice and that there may not be water on Mars after all.
This series of images from the HiRISE camera on NASA's Mars Reconnaissance Orbiter shows warm-season features that might be evidence of salty liquid water active on Mars today.
Once again the world is abuzz about water on Mars. Sure, we already
that there's a plentiful supply of water ice at the Red Planet's poles; we
that approximately 2 percent of the Martian regolith (at Mars rover Curiosity's location in any case) is composed of water; we also
that ancient Mars was a wet world, possessing rivers, lakes and even seas -- according to the sedimentary rock and minerals that could have only been formed in an abundance of liquid water. But now NASA has found pretty solid evidence that the seasonal short-lived, dark channels seen on steep slopes are formed by salty liquid water gushing over the apparently barren Mars surface
Shown here is a 3-D map of the slopes of Hale Crater which is based on observations by the High-Resolution Imaging Science Experiment (HiRISE) camera on board NASA's Mars Reconnaissance Orbiter. The dark channels running down the slopes are known as "recurring slope lineae," and they could be one of the biggest hints yet that some form of basic, yet extreme, microbe may use that water as a means to eke out an existence just below the surface.
After arriving in Mars orbit in 2006, the Mars Reconnaissance Orbiter began an epic campaign of observing the surface in high resolution. In 2011,
the formation of recurring slope lineae, or RSLs, as the southern hemisphere passed from winter to summer. Like drips running down a melting ice cream cone, these dark features resembled flowing liquid water on the Martian surface. However, the finding was not conclusive.
Surface missions to the Red Planet have gradually been forming a picture of the chemicals in the Mars soil, or regolith. Of particular note was the 2008 NASA Phoenix Mars lander that uncovered evidence for droplets of liquid water on the surface. However, liquid water should be impossible on current-day Mars; the atmospheric pressure and temperature is too low for liquid water to persist, water either exists in a solid (ice) or gaseous (vapor) state. Ice doesn't melt on the Martian surface, it sublimates, like carbon dioxide ice (a.k.a. "dry ice") does at room temperature on Earth. The possibility of liquid water on the surface as seen by Phoenix added credence to the possibility that the surface must be rich in a highly toxic salts, known as perchlorates. When mixed with water, these salts lower water's freezing point, potentially allowing liquid water to persist in pools just under the surface, despite the chilly conditions. Since then, NASA's Curiosity has also uncovered evidence for perchlorates laced in the soil.
Image: More evidence for RSLs in Garni Crater, as dramatically shown in this 3-D map constructed from HiRISE data.
Perchlorates form the key behind Monday's grand announcement. Through the use of another instrument on board the Mars Reconnaissance Orbiter, a spectrometer called CRISM (Compact Reconnaissance Imaging Spectrometer for Mars), and using a new analysis technique, scientists have been able to study the chemical composition of these dark RSL channels. What they found was the chemical signatures of hydrated salts -- basically the residue of perchlorates left behind after surges of salty water, known as "brines."
Although exciting, the source of these brines apparently supplying the RSL channels is something of a mystery. Scientists point to the possibility of the seasonal melting sub-surface ice, or perhaps moisture from the atmosphere somehow condensing to supply the flow of water, but neither explanation is satisfactory.
Image: An oblique view from the Mars Reconnaissance Orbiter of slopes in Newton Crater, highlighting warm season flows in Newton Crater.
This may be strong evidence for liquid water flows on the surface of Mars, potentially revealing sub-surface aquifers under an otherwise barren landscape, but scientists are quick to point out that these brines are not particularly conducive to life, at least
life as we know it.
The extreme salinity of the water causing the RSLs would likely be too dense for the survival, let alone evolution, of microbes. But on Earth, despite its toxicity, some microbes in desert locations use perchlorate salts as an energy source. Regardless, the location of these possible outflows would make it very difficult for us to send robotic explorers to check them out. Although researchers are hopeful that perhaps Curiosity may find some RSLs of its own on the slopes of Mount Sharp in Gale Crater, the best way to study them is, currently, from orbit. But it would be nice if we could send a human expedition to the Red Planet to check out these outflows first-hand.