Large Reservoir of Liquid Water Found Deep Below the Surface of Mars

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Artist impression of the Mars Express spacecraft probing the southern hemisphere of Mars, superimposed on a radar cross section of the southern polar layered deposits. The leftmost white line is the radar echo from the Martian surface, while the light blue spots are highlighted radar echoes along the bottom of the ice.  Those highlighted areas measure very high reflectivity, interpreted as being caused by the presence of water. (ESA, INAF. Graphic rendering by Davide Coero Borga )

Far beneath the frigid surface of the South Pole of Mars is probably the last place where you might expect the first large body of Martian liquid water would be found.  It’s -170 F on the surface, there are no known geothermal sources that could warm the subterranean ice to make a meltwater lake, and the liquid water is calculated to be more than a mile below the surface.

Yet signs of that liquid water are what a team of Italian scientists detected — a finding that they say strongly suggests that there are other underground lakes and streams below the surface of Mars.  In a Science journal article released today, the scientists described the subterranean lake they found as being about 20 kilometers in diameter.

The detection adds significantly to the long-studied and long-debated question of how much surface water was once on Mars, a subject that has major implications for the question of whether life ever existed on the planet.

Finding the subterranean lake points to not only a wetter early Mars, said co-author Enrico Flamini of the Italian space agency, but also to a Mars that had a water cycle that collected and delivered the liquid water.  That would mean the presence of clouds, rain, evaporation, rivers, lakes and water to seep through surface cracks and pool underground.

Scientists have found many fossil waterways on Mars, minerals that can only be formed in the presence of water, and what might be the site of an ancient ocean.

But in terms of liquid water now on the planet, the record is thin.  Drops of water collected on the leg of NASA’s Phoenix Lander after it touched down in 2008, and what some have described as briny water appears to be flowing down some steep slopes in summertime.  Called recurrent slope lineae or RSLs, they appear at numerous locations when the temperatures rise and disappear when they drop.

This lake is different, however, and its detection is a major step forward in understanding the history of Mars.

Color photo mosaic of a portion of Planum Australe on Mars.  The subsurface reflective echo power is color coded and deep blue corresponds to the strongest reflections, which are interpreted as being caused by the presence of water. (USGS Astrogeology Science Center, Arizona State University, INAF)

The discovery was made analyzing echoes captured by the the radar instruments on the European Space Agency’s Mars Express, a satellite orbiting the planet since 2002.  The data for this discovery was collected from observation made between 2012 and 2015.

 

A schematic of how scientists used radar to find what they interpret to be liquid water beneath the surface of Mars. (ESA)

Antarctic researchers have long used radar on aircraft to search for lakes beneath the thick glaciers and ice layers,  and have found several hundred.  The largest is Lake Vostok, which is the sixth largest lake on Earth in terms of volume of water.  And it is two miles below the coldest spot on Earth.

So looking for a liquid lake below the southern pole of Mars wasn’t so peculiar after all.  In fact, lead author Roberto Orosei of the Institute of Radioastronomy of Bologna, Italy said that it was the ability to detect subsurface water beneath the ice of Antarctica and Greenland that helped inspire the team to look at Mars.

There are a number of ways to keep water liquid in the deep subsurface even when it is surrounded by ice.  As described by the Italian team and an accompanying Science Perspective article by Anja Diez of the Norwegian Polar Institute, the enormous pressure of the ice lowers the freezing point of water substantially.

Added to that pressure on Mars is the known presence of many salts, that the authors propose mix with the water to form a brine that lowers the freezing point further.

So the conditions are present for additional lakes and streams on Mars.  And according to Flamini, solar system exploration manager for the Italian space agency, the team is confident there are more and some of them larger than the one detected.  Finding them, however, is a difficult process and may be beyond the capabilities of the radar equipment now orbiting Mars.

 

Subsurface lakes and rivers in Antarctica. Now at least one similar lake has been found under the southern polar region of Mars. (NASA/JPL)

The view that subsurface water is present on Mars is hardly new.  Stephen Clifford, for many years a staff scientist at the Lunar and Planetary Institute, even wrote in 1987 that there could be liquid water at the base of the Martian poles due to the kind of high pressure environments he had studied in Greenland and Antarctica.

So you can imagine how gratifying it might be to learn, as he put it “of some evidence that shows that early theoretical work has some actual connection to reality.”

He considers the new findings to be “persuasive, but not definitive” — needing confirmation with other instruments.

Clifford’s wait has been long, indeed.  Many observations by teams using myriad instruments over the years did not produce the results of the Italian team.

Their discovery of liquid water is based on receiving particularly strong radar echoes from the base of the southern polar ice — echoes consistent with the higher radar reflectivity of water (as opposed to ice or rock.)

After analyzing the data in some novels ways and going through the many possible explanations other than the presence of a lake, Orosei said that none fit the results they had.  The explanation, then, was clear:  “We have to conclude there is liquid water on Mars.”

The depth of the lake — the distance from top to bottom — was impossible to measure, though the team concluded it was at least one meter and perhaps in the tens of meters.

Might the lake be a habitable?  Orosei said that because of the high salt levels “this is not a very pleasant environment for life.”

But who knows?  As he pointed out, Lake Vostok and other subglacial Antarctic lake, are known to be home to single-cell organisms that not only survive in their very salty world, but use the salt as part of their essential metabolism.

 

 

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The Mars Water Story Gets Ever More Interesting

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Enchanced-color traverse section of Martian icy scarps in late spring to early summer. Arrows indicate locations where relatively blue material is particularly close to the surface. Image taken by HiRISE camera on Mars Reconnaissance Orbiter. (NASA/JPL/UNIVERSITY OF ARIZONA/USGS )

Huge escarpments of quite pure water ice have been found in the Southern Highlands of Mars — accessible enough that astronauts might some day be able to turn the ice into water, hydrogen and oxygen.

Some of these deposits are more than 100 meters thick and begin only a meter or two below the surface.

These are among the conclusion from a new paper in the journal Science that describes these previously unknown water ice reserves.  While Mars scientists have long theorized the presence of subsurface ice under one-third of the planet, and even exposed bits of it with the Phoenix lander, the consensus view was that Martian ice was generally cemented with soil to form a kind of permafrost.

But the “scarp” ice described by Colin Dundas of the U.S. Geological Survey and colleagues is largely water ice without much other material.  This relative purity, along with its accessibility, would make the ice potentially far more useful to future astronauts.

“The ice exposed by the scarps likely originated as snow that transformed into massive ice sheets, now preserved beneath less than 1 to 2 meters of dry and ice-cemented dust or regolith,” the authors write. The shallow depths, the write “make the ice sheets potentially accessible to future exploration.”

The bright red regions contain water ice, as determined by measurements by the High-Resolution Imaging Science Experiment (HiRISE) on NASA’s Mars Reconnaissance Oribter. (NASA)

The importance is clear:  These sites are “very exciting” for potential human bases as well, says Angel Abbud-Madrid, director of the Center for Space Resources at the Colorado School of Mines in Golden, who led a recent NASA study exploring potential landing sites for astronauts.

Water is a crucial resource for astronauts, because it could be combined with carbon dioxide, the main ingredient in Mars’s atmosphere, to create oxygen to breathe and methane, a rocket propellant. And although researchers suspected the subsurface glaciers existed, they would only be a useful resource if they were no more than a few meters below the surface. The ice cliffs promise abundant, accessible ice, Abbud-Madrid told Science Magazine.

While the discovery adds to the view that Mars is neither bone-dry now nor was earlier in its history, it does not necessarily add to the question of where all the Martian water has gone or how much was originally there.

That’s because the paper describes the huge ice deposits as the result of snowfall over more recent eons that was packed into its current form, rather than water that might have been present during the warmer wetter periods of Mars history. With this in mind, Dundas said in an email that his team’s work does not add to what is known about the early Mars water budget.

As for the age of the water ice, he said “we can’t put an accurate number on it at this time, but the icy units are lightly cratered. Others in the community have proposed snowfall during periods of high axial tilt within the last few million years.”

So the ice is relatively young. But that doesn’t mean it has no story to tell.  Exposed ice, like exposed rock, always has a story to tell.

“We expect the vertical structure of Martian ice-rich deposits to preserve a record of ice deposition and past climate,” the authors write.

The eight scarps studied were steep and faced the poles. All were in the mid-latitudes, and therefore far from the polar ice sheets.

The lander Phoenix dug into the soil of the northern polar region and found cemented ice as well as pure ice several inches down. (NASA)

NASA has long had a motto for exploring Mars and other sites beyond Earth of “follow the water.”  That has been expanded to “follow the carbon” and “follow the organics,” but the water is still a guidepost of sorts of where life, or its remnants, might be found.  Now with these large and seemingly accessible deposits of water ice, “follow the water” takes on a new meaning for potential future astronauts in search of essential chemical components.

Still, the issue of just how much water there is and has been on Mars is a central to piecing together the planet’s history and how much of the planet might have one day been eminently habitable.

The last decade of Mars exploration and observation has led most Mars scientists to conclude that the planet once had rivers, lakes and possibly a northern ocean. That water is almost entirely (or perhaps entirely) gone from the surface now, and understanding where it went is certainly key to understanding the history of the planet.

While much no doubt escaped to space after the early protective Mars magnetic field and atmosphere largely disappeared, researchers say there remains a lot of Mars water to be accounted for.

An article in the journal Nature last month reported the possibility of large amounts of water mixing with Martian basalts long ago and forming a broadly water-rich crust.  The authors of that paper, led by Jon Wade of Oxford’s Department of Earth Sciences, described modeling that found water on early Mars could be absorbed into spongy rock at a far greater rate than on Earth.

In an accompanying review, geochemist and cosmochemist Tomohiro Usui of the Earth-Life Science Institute in Tokyo, supported the notion, and added another possibility that he has published on as well.

“Ground ice might also account for the missing water reservoir on Mars,” he wrote. “Subsurface radar-sounder measurements have detected an anomaly in an electrical property of rocks in the planet’s northern hemisphere, which implies that massive ice deposits are embedded among or between layers of sediment and volcanic materials at a depth of 60–80 m.”

Usui wrote that the ground-ice model has also been proposed based of analyses of hydrogen isotopes in Martian meteorites and of the shapes and characteristics of craters. Indeed, the crater study indicated that the subsurface water ice has a volume comparable to the size of the ancient oceans.

Where did the large amounts of water once present on Mars go. Some clearly was lost to the atmosphere, but some researchers are convinced that much is underground as ice or incorporated into minerals. (Nature)

 

Dundas agreed that the new paper was a continuation of earlier work, rather than something entirely new. “We’ve known for some time that there is shallow ground ice within a meter of the surface, and there have been recent radar detections of ice sheets tens of meters thick,” he said in his email. “What our work does is provide some three-dimensional information at high resolution that helps tie things together.”

Dundas et al reported that the fractures and steep angles found indicate that the ice is cohesive and strong. What’s more, bands and variations in color suggest that the ice contains distinct layers, which could be used to understand changes in Mars’ climate over time.

Because the ice is only visible where surface soil has been removed, the paper says it is likely that ice near the surface is more extensive than detected in this study.

And that could be very important to astronauts on future missions to Mars.

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