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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Two Tempting Reprise Missions: Explore Titan or Bring Back a Piece of A Comet

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Dragonfly is a quadcopter lander that would take advantage of the environment on Titan to fly to multiple locations, some hundreds of miles apart, to sample materials and determine the composition of the surface.  A central goal would be to analyze Titan’s organic chemistry and assess its habitability. (NASA)

Unmanned missions to planets and moons and asteroids in our solar system have been some of NASA’s most successful efforts in recent years, with completed or on-going ventures to Mars, Saturn, Jupiter, the asteroid Bennu, our moon, Pluto, Mercury and bodies around them all.   On deck are a funded mission to Europa, another to Mars and one to the unique metal asteroid 16 Psyche orbiting the sun between Mars and Jupiter.

We are now closer to adding another New Frontiers class destination to that list, and NASA announced this week that it will be to either Saturn’s moon Titan or to the comet 67P/Churyumov-Gerasimenko.

After assessing 12 possible New Frontiers proposals, these two made the cut and will receive $4 million each to further advance their proposed science and technology. One of them will be selected in spring of 2019 for launch in the mid 2020s.

With the announcement, associate administrator for NASA’s Science Mission Directorate Thomas Zurbuchen described the upcoming choice as between two “tantalizing investigations that seek to answer some of the biggest questions in our solar system today.”

Those questions would be:  How did water and other compounds essential for life arrive on Earth?  Comets carry ancient samples of both, and so can potentially provide answers.

And with its large inventories of nitrogen, methane and other organic compounds, is Titan potentially habitable?  Then there’s the added and very intriguing prospect of visiting the methane lakes of that frigid moon.

The CAESAR mission would return to the nucleus of  comet explored by the European Space Agency’s Rosetta mission, and its lander Philae.  (NASA)

Both destinations selected have actually been visited before.

The European Space Agency’s Rosetta mission orbited the comet 67P/Churyumov-Gerasimenko comet for two years and deployed a lander, which did touch down but sent back data for only intermittently for several days.

And the NASA’s Cassini-Huygens mission to Saturn passed by Titan regularly during its decade exploring that system, and the ESA’s Huygens probe did land on Titan and sent back information for a short time.

So both Rosetta and Cassini-Huygens began the process of understanding these distant and potentially revelatory destinations, and now NASA is looking to take it further.

The Titan “Dragonfly” mission, for instance, would feature a “quadcopter” or “rotorcraft” — a vehicle that is part helicopter and part drone.  It’s designed to hop hundreds of miles around the moon to sample what has already been determined to be a surface with many organic compounds and liquid methane lakes.

Those already identified hydrocarbon seas may contain amino acids and other interesting molecules, making Titan a test bed of sorts on how life arose on Earth. With spectrometers, drills, and cameras, Dragonfly would split its mission between science in the air and on the ground.

Although frigid, Titan is otherwise now known to be a relatively benign place, and the rotorcraft could potentially survive for several years. That could give the team time to “evaluate how far prebiotic chemistry has progressed in an environment where we know we have the ingredients for life,” said lead investigator Elizabeth Turtle from the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland.

“Titan is a unique ocean world, with lakes and rivers of liquid methane flowing across its surface,” she said.  But it is also very cold. Average surface temperatures are -290 degrees Fahrenheit,  so any potential lifeforms would face some major challenges.

A methane lake near the northern pole of Saturn’s moon, Titan. The image was taken using radar on the Cassini spacecraft. NASA/JPL-Caltech

The comet mission CAESAR (Comet Astrobiology Exploration SAmple Return) will take a very different route than Rosetta did and will use different propulsion that will get the spacecraft to the comet in four years.  The plan is to then perform a “touch and go” maneuver with an extended arm to pick up 100 grams of precious Rosetta material from the nucleus.

And then unlike with Rosetta, the plan is to cache the sample and bring it back to Earth for intensive study.

By returning to 67P/Churyumov-Gerasimenko, a body mapped in detail by Rosetta, the mission is “able to design our spacecraft specifically for the conditions we know,” said Steven Squyres of Cornell University, principal investigator for the mission.

During a news conference, Squyres said that “comets are among the most scientifically important objects in the solar system, but they’re also among the most poorly understood.

“They’re the most primitive building blocks of planets; they contain materials that date from the very earliest moments of solar system formation and even before. Comets were a source of water for the Earth’s oceans, and critically they were a source of organic molecules that contributed to the origin of life.”

Squyres told me after the announcement that the CAESAR instruments will allow for more precise measurements than from Rosetta, and that a successful sample return could potentially change our understanding of the Earth’s history substantially.  He said the sample collection would also importantly include gases.

NASA has already succeeded with comet sample return — the Stardust mission to fly through the plume of comet Wild-2.  It did gather some dust, but it didn’t land on the nucleus like Rosetta did and CAESAR would.

Sample return is clearly a high priority for NASA and other space agencies.  The NASA 2020 mission to Mars is designed to collect and cache rock samples for later return, and two other sample return missions are underway.  Both are to asteroids, with one launched last year by NASA and the other by the Japanese space agency JAXA in 2014.

The nucleus of the 67P/Churyumov-Gerasimenko comet, where the CAESAR mission hopes to be headed in the 2020s. (ESA)

What “Dragonfly” would return is data about a moon shrouded in haze and unlike any other body in our solar system.

When the Huygen’s probe descended to the moon in early 2005, planetary scientists weren’t sure if the moon’s surface was covered in oceans methane and ethane.  So Huygens was designed to float if solid ground wasn’t to be found.

As the lander sailed through the haze it took hundreds of aerial images that showed an alien but strikingly Earth-like landscape of mountains, dry floodplains and what appeared to be river deltas. Huygens did land on something solid, though liquid methane flowed nearby and the Huygens cameras could see intricate channels cutting into the surface.

When Huygens touched down, it did so with a soft thud and a short slide across the frozen surface. Later analysis of the lander’s telemetry showed that Huygens sank around 4.7 inches into the surface on first contact, bounced and slid before coming to a stop.

This knowledge made possible a Titan project with a lander that can jump from one spot to another quite far away.  Those methane lakes, it is now understood, are largely found near the northern pole, and so floatation equipment is no longer necessary.

The Huygens descent to the surface of Titan, as recorded in 2005.  (ESA/NASA)

Squyres, a professor of physical science at Cornell University, is also principal investigator for the long-lasting Mars exploration rovers, one of which operated successfully for 8 years and the other –Opportunity — is still exploring Mars 13 years after landing.

He told me that his long years heading the Mars rover mission had convinced him that his greatest satisfaction in science comes from identifying a plausible space project, putting together a team of scientists, engineers and managers who can plausibly pull it off, and then work nonstop for years putting together a proposal to get it selected and funded. His team now numbers about 150 people and will soon grow much larger.

It was that sense of “shared struggle,” he said, that gave him enormous satisfaction. That came, of course, with a happy ending in several competitions, but he said he also knows the disappointment of not being selected for others.

Two other missions were selected for additional, though limited, funding under the New Frontiers program.  One is headed by NASA Ames Research Center astrobiologist Chris McKay and will be funded to develop “cost-effective techniques that limit spacecraft contamination and thereby enable life detection measurements on cost-capped missions.”

The larger mission his team proposed would go to the water vapor plume spurting out of Saturn’s moon Enceladus, with the goal of searching for signs of life.

The two projects selected were no doubt something of a disappointment to researchers who have longed for NASA to return to Venus.  As the study of exoplanets progresses, one of the key questions facing scientists is why Earth and Venus evolved so differently.  Both are within our sun’s habitable zone, but Venus experienced a runaway greenhouse effect that parched the surface and pushed surface temperatures to a led-melting 870 degrees F.

Three of the proposed New Frontiers missions were to Venus but, as in other recent competitions, none were selected by NASA.  One of the Venus proposals, led by Goddard’s Lori Glaze, was selected for further technology development.

Venus hasn’t been visited by a NASA spacecraft in decades, leading to hopes that one of the New Frontiers finalists would be a mission there. But it was not to be. ESA operated the Venus Express mission orbiting the planet from 2006 to 2014 and the Japanese Space Agency has a probe (Akatsuki) here now. (NASA)

Also noticeably absent among the finalists was any pr0ject going to the moon, especially since the Trump administration has made a lunar colony a priority.  Apparently a New Frontiers mission is not what the administration has in mind.

New Frontiers initiative is the largest NASA planetary exploration program open to outside competition and leadership.  But NASA does set the priorities, as put forward by the planetary science and astrobiology communities.

Previous spacecraft launched under New Frontiers include New Horizons, which surveyed Pluto and is now due to visit MU69, an icy object in the farthest reaches of the solar system; Juno, now in orbit around Jupiter; and OSIRIS-REx, launched last year, which will collect samples from an asteroid and return them to Earth.

Since the New Frontiers program began at the beginning of the century, NASA has selected two missions for each decade, making them the most frequent of the major agency missions.  Costs are capped at $1 billion — with $850 million for the mission and $150 million for the launch.  So far, the money has been demonstrably well spent.

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Cassini Inside the Rings of Saturn

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Movie produced from images taken while Cassini flew inside the rings of Saturn – a first. (NASA/JPL-Caltech/Space Science Institute)

The triumphant Cassini mission to Saturn will be coming to an end on September 15, when the spacecraft dives into the planet.  Running out of fuel, NASA chose to end the mission that way rather than run the risk of having the vehicle wander and ultimately land on Europa or Enceladus, potentially contaminating two moons very high on the list of possible habitable locales in our solar system.

Both the science and the images coming back from this descent are (and will be) pioneering, as they bring to an end one of the most successful and revelatory missions in NASA history.

As NASA promised, the 22-dive descent has already produced some of the most compelling images of Saturn and its rings.  Most especially, Cassini has delivered the remarkable 21-image video above.  The images were taken over a four minutes period on August 20 using a wide-angle camera.

The spacecraft captured the images from within the gap between the planet and its rings, looking outward as the spacecraft made one of its final dives through the ring-planet gap as part of the finale.

The entirety of the main rings can be seen here, but due to the low viewing angle, the rings appear extremely foreshortened. The perspective shifts from the sunlit side of the rings to the unlit side, where sunlight filters through.

On the sunlit side, the grayish C ring looks larger in the foreground because it is closer; beyond it is the bright B ring and slightly less-bright A ring, with the Cassini Division between them. The F ring is also fairly easy to make out.

 

NASA’s Cassini spacecraft will make 22 orbits of Saturn during its Grand Finale, exploring a totally new region between the planet and its rings. NASA/JPL-Caltech

While the Cassini team has to keep clear of the rings, the spacecraft is expected to get close enough to most likely answer one of the most long-debated questions about Saturn: how old are those grand features, unique in our solar system?

One school of thought says they date from the earliest formation of the planet, some 4.6 billion years ago. In other words, they’ve been there as long as the planet has been there.

But another school says they are a potentially much newer addition. They could potentially be the result of the break-up of a moon (of which Saturn has 53-plus) or a comet, or perhaps of several moons at different times. In this scenario, Saturn may have been ring-less for eons.

As Curt Niebur, lead program scientist at NASA headquarters for the Cassini mission, explained it, the key to dating the rings is a close view of, essentially, how dirty they are. Because small meteorites and dust are a ubiquitous feature of space, the rings would have significantly more mass if they have been there 4.6 billion years. But if they are determined to be relatively clean, then the age is likely younger, and perhaps much younger.

“Space is a very dirty place, with dust and micro-meteorites hitting everything. Over significant time scales this stuff coats things. So if the rings the rings are old, we should find very dirty ice. If there is little covering of the ice, then the rings must be young. We may well be coming to the end of a great debate.”

 

Cassini gazes across the icy rings of Saturn toward the icy moon Tethys, whose night side is illuminated by Saturnshine, or sunlight reflected by the planet. Tethys was on the far side of Saturn with respect to Cassini here; an observer looking upward from the moon’s surface toward Cassini would see Saturn’s illuminated disk filling the sky. Tethys was brightened by a factor of two in this image to increase its visibility. A sliver of the moon’s sunlit northern hemisphere is seen at top. A bright wedge of Saturn’s sunlit side is seen at lower left. (NASA/JPL-Caltech/Space Science Institute)

A corollary of the question of the age of Saturn’s rings is, naturally, how stable they are.

If they turn out to be as old as the planet, then they are certainly very stable.  But if they are not old then it is entirely plausible that they could be a passing phenomenon and will some day disappear — to perhaps re-appear after another moon is shattered or comet arrives.

Another way of looking at the rings is that they may well have been formed at different times.

As project scientist Linda Spilker explained in an email, Cassini’s measurements of the mass of the rings will be key.  “More massive rings could be as old as Saturn itself while less massive rings must be young.  Perhaps a moon or comet got too close and was torn apart by Saturn’s gravity.”

The voyage between the rings will also potentially provide some new insights into the workings of the disks present at the formation of all solar systems.

“The rings can teach us about the physics of disks, which are huge rings floating majestically and with synchronicity  around the new sun,” Niebur said.  “That said, the rings of Saturn have a very active regime, with particles and meteorites and micrometeorites smacking into each other.  It’s an amazing environment and has direct relevance to the nebular model of planetary formation.”

The view above was acquired at a distance of approximately 750,000 miles (1.2 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 140 degrees. . The distance to Tethys was about 930,000 miles (1.5 million kilometers).

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for NASA and the imaging operations center is based at the Space Science Institute in Boulder, Colorado.

 

Polar region of Saturn, with tumultuous cloud pattern. A bizarre six-sided feature encircling the north pole of Saturn was identified earlier using the visual and infrared mapping spectrometer on NASA’s Cassini spacecraft.(NASA/JPL-Caltech/Space Science Institute)

Among the areas of greatest interest during the final descent are the turbulent clouds on the North Pole of Saturn.  Cassini captured this view of the pole on April 26, 2017 – the day it began its grand finale — as it approached the planet for its first dive through the gap between the planet and its rings.

Although the pole is still bathed in sunlight at present, northern summer solstice on Saturn occurred on May 24, 2017, bringing the maximum solar illumination to the north polar region. Now the Sun begins its slow descent in the northern sky, which eventually will plunge the north pole into Earth-years of darkness. Cassini’s long mission at Saturn enabled the spacecraft to see the Sun rise over the north, revealing that region in great detail for the first time.

This view looks toward the sunlit side of the rings from about 44 degrees above the ring plane. The image was taken with the Cassini spacecraft wide-angle camera using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.

Saturn boasts some unique features in its atmosphere. When the Voyager missions traveled to the planet in the early 1980s, it imaged a hexagon-shaped cloud formation near the north pole.

Twenty-five years later, infrared images taken by Cassini revealed the storm was still spinning, powered by jet streams that push it to speeds of about 220 mph (100 meters per second). At 15,000 miles (25,000 km) across, the long-lasting storm could easily contain an Earth or two.

The recent view was obtained at a distance of approximately 166,000 miles (267,000 kilometers) from Saturn.

But because Saturn is a gas giant and has no defined surface per se, it’s difficult to describe exactly how far from the planet Cassini might be traveling at any given time.

On the final orbit, Cassini will plunge into Saturn’s atmosphere, sending back new and unique science to the very end. After losing contact with Earth, the spacecraft will burn up like a meteor, becoming part of the planet itself.

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