At a press conference today, NASA announced exciting news that the world has been waiting for: water on Mars. The findings from the Mars Reconnaissance Orbiter (MRO) provide the strongest evidence yet that liquid water flows intermittently on the surface of present-day Mars.
“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, astronaut and associate administrator at NASA.
“This is a significant development, as it appears to confirm that water — albeit briny — is flowing today on the surface of Mars,” said Grunsfeld.
Using the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on MRO, researchers detected signatures of hydrated minerals on slopes where mysterious streaks are seen on the Red Planet.
First appearing in images from MRO’s High Resolution Imaging Science Experiment (HiRISE) as far back as 2010, these darkish streaks appear to ebb and flow over time. Additionally, they have been documented at a number of sites on Mars.
The streaks darken and appear to flow down steep slopes during warm seasons, and then fade in cooler seasons. They appear in several locations on Mars when temperatures are above minus 10 degrees Fahrenheit (minus 23 degrees Celsius), and disappear during colder times.
These downhill flows, known as recurring slope lineae (RSL), have often been described as possibly related to liquid water. HiRISE observations of RSL were compared with mineral mapping by CRISM. This led to the new findings of hydrated salts on the slopes and pointed to what the relationship of these dark features might be.
Dark narrow streaks called recurring slope lineae emanating out of the walls of Garni crater on Mars. The dark streaks here are up to a few hundred meters in length. They are hypothesized to be formed by the flow of briny liquid water on Mars. Vertical exaggeration is 1.5. (Photo courtesy of NASA/JPL/University of Arizona.)
Due to the freezing point depression property, the hydrated salts would lower the freezing point of water, now in a liquid brine. The process is the same as salt on frozen roads.
Scientists say it is most likely a shallow subsurface flow, with enough water wicking to the surface to cause the visible darkening.
The spectrometer observations show signatures of hydrated salts at multiple RSL locations, but only when the dark features were relatively wide.
When the researchers looked at the same locations and RSL weren't as extensive, they detected no hydrated salt.
Lujendra Ojha and co-authors at the Georgia Institute of Technology in Atlanta interpreted the spectral signatures as being caused by hydrated minerals called perchlorates.
The hydrated salts most consistent with the spectrographic chemical signatures are a mixture of magnesium perchlorate, magnesium chlorate and sodium perchlorate.
Some perchlorates have been shown to keep water from freezing even when conditions are as cold as minus 94 degrees Fahrenheit (minus 70 degrees Celsius). On Earth, naturally produced perchlorates are concentrated in deserts.
Perchlorates have previously been detected on Mars. NASA's Phoenix lander and Curiosity rover both found them in the planet's soil, and some scientists believe that the Viking missions in the 1970s measured signatures of these salts.
However, this study of RSL detected perchlorates, now in hydrated form, in different areas than those explored by the landers. This is also the first time perchlorates have been identified from orbit.
The abundance of perchlorates may create difficulties for human exploration and settlement on Mars, as they are toxic to humans, causing thyroid problems and other health effects.
However, perchlorates can also be an opportunity to lighten the load planetary explorers will need to bring for a manned mission to Mars.
Some types of perchlorates can be used as rocket propellant and the high oxygen content can be chemically separated out of perchlorates to make breathable air, or reacted with hydrogen to produce additional water, similar to what is described in Andy Weir’s The Martian. With the addition of liquid water on Mars, the only thing explorers might need to bring for survival is food.
"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. In either case, the detection of hydrated salts on these slopes means that water plays a vital role in the formation of these streaks," said Ojha. His paper on the discovery will be published September 28 by Nature Geoscience.
MRO has been examining Mars since 2006 with its six science instruments.
"The ability of MRO to observe for multiple Mars years with a payload able to see the fine detail of these features has enabled findings such as these: first identifying the puzzling seasonal streaks and now making a big step towards explaining what they are," said Rich Zurek, MRO project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.
For Ojha, the new findings are more proof that the mysterious lines he first saw darkening Martian slopes five years ago are, indeed, present-day water.
"When most people talk about water on Mars, they're usually talking about ancient water or frozen water," Ojha said. "Now we know there’s more to the story. This is the first spectral detection that unambiguously supports our liquid water-formation hypotheses for RSL."
The discovery is the latest of many exciting discoveries by NASA’s Mars missions.
“It took multiple spacecraft over several years to solve this mystery, and now we know there is liquid water on the surface of this cold, desert planet,” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program. “It seems that the more we study Mars, the more we learn how life could be supported and where there are resources to support life in the future.”
This news of water on Mars crowns existing excitement over the next Mars 2020 rover mission, as well as NASA’s Journey to Mars mission to send humans to the red planet by the 2030s.
For more on NASA’s Mars Reconnaissance Orbiter mission, visit the MRO mission page.