The Ancient Lakes of Mars –Could They Reveal Signs of Former Life?

 

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A new survey of ancient lakebeds in the Nili Fossae region of Mars (above) revealed that only a third show evidence of deposits of mud and clay on the surface today. If life evolved on Mars, deposits of clay and sediment could contain fossil evidence of its existence as they have on Earth.


A team of scientists at Brown University pored over surface images from the Mars Reconnaissance Orbiter, the Mars Odyssey Spacecraft, and the Mars Express spacecraft in search of lakes that once boasted water but found that only 79 of the beds contained deposits of minerals that hint at clays on the surface.  

The image at the bottom of the page shows the location of 226 ancient lakes spread across the Martian surface, north and south of the Equator. The Nili Fossae region, circled, contains an unusually high density of sedimentary deposits, likely caused by the large degree of erosion in the area.

This August, Curiosity, NASA's car-sized rover, also known as the Mars Science Lab, will land at the foot of a three-mile high mountain in a crater named Gale after its eight-month voyage to the Red Planet. Because of its history, this 96 mile wide crater with its strangely sculpted mountain –three times higher than the Grand Canyon is deep–is the ideal place for Curiosity to conduct its mission of exploration into the Red Planet's past. 

"Gale Crater and its mountain will tell this intriguing story, The layers there chronicle Mars' environmental history," said Matthew Golombek, Mars Exploration Program Landing Site JPL Scientist.

"This may be one of the thickest exposed sections of layered sedimentary rocks in the solar system," explained Joy Crisp, MSL Deputy Project Scientist from NASA's Jet Propulsion Laboratory. "The rock record preserved in those layers holds stories that are billions of years old — stories about whether, when, and for how long Mars might have been habitable."

An instrument on Curiosity can check for any water that might be bound into shallow underground minerals along the rover's path.

"If we conclude that there is something unusual in the subsurface at a particular spot, we could suggest more analysis of the spot using the capabilities of other instruments," said this instrument's principal investigator, Igor Mitrofanov of the Space Research Institute, Russia.

Today the Red Planet is a radiation-drenched, bitterly cold, bleak world. Enormous dust storms explode across the barren landscape and darken Martian skies for months at a time. But data from the Mars Reconnaissance Orbiter suggest that Mars once hosted vast lakes and flowing rivers.

In the gentle slopes around the mountain, Curiosity will prospect for organic molecules, the chemical building blocks of life. Mars Reconnaissance Orbiter has found an intriguing signature of clay near the bottom of the mountain and sulfate minerals a little higher up. Both minerals are formed in the presence of water, which increases potential for life-friendly environments.

"All the types of aqueous minerals we've detected on Mars to date can be found in this one location," explains Golombek.

Clay settles slowly in water and forms little platelets that conform around things, hardening over time and encasing them in ''casts." Clay could seal organics off from the outside environment much like it preserved dinosaur bones on Earth. "If organics ever existed on Mars, they could be preserved in the clay," added Golombek.

Even on planet Earth, teeming with life, finding billion year-old well-preserved organics is difficult. But Curiosity will find them if they're present in the samples it takes. The rover is equipped with the most advanced suite of instruments for scientific studies ever sent to the Martian surface1. When these are brought to bear on Gale crater’s mysteriously layered mountain, the odds of a discovery will be at an all-time high.

As seasoned travelers know, however, the journey is just as important as the destination. Curiosity can travel up to 150 meters per Mars day, but will stop often to gather and analyze samples.

"It could take several months to a year to reach the foot of the mountain, depending on how often the rover stops along the way," says Golombek. "There will be plenty to examine before getting to the central mound."

The Mars Science Laboratory mission will use 10 instruments on Curiosity to investigate whether the area selected for the mission has ever offered environmental conditions favorable for life and favorable for preserving evidence about life.

"The strength of Mars Science Laboratory is the combination of all the instruments together," Mitrofanov stressed.

The Dynamic Albedo of Neutrons instrument, or DAN, will scout for underground clues to a depth of about 20 inches (50 centimeters).

DAN will bring to the surface of Mars an enhancement of nuclear technology that has already detected Martian water from orbit. "Albedo" in the instrument's name means reflectance — in this case, how original high-energy neutrons injected into the ground bounce off atomic nuclei in the ground. Neutrons that collide with hydrogen atoms bounce off with a characteristic decrease in energy, similar to how one billiard ball slows after colliding with another. By measuring the energies of the neutrons leaking from the ground, DAN can detect the fraction that was slowed in these collisions, and therefore the amount of hydrogen.

Oil prospectors use this technology in instruments lowered down exploration holes to detect the hydrogen in petroleum. Space explorers have adapted it for missions to the moon and Mars, where most hydrogen is in water ice or in water-derived hydroxyl ions. 

Mitrofanov is the principal investigator for a Russian instrument on NASA's Mars Odyssey orbiter, the high-energy neutron detector (HEND), which measures high energy of neutrons coming from Mars. In 2002, it and companion instruments on Odyssey detected hydrogen interpreted as abundant underground water ice close to the surface at high latitudes. That discovery led to NASA's Phoenix Mars Lander going to far northern Mars in 2008 and confirming the presence of water ice.

"You can think of DAN as a reconnaissance instrument," Mitrofanov said. Just as Phoenix investigated what Odyssey detected, Curiosity can use various tools to investigate what DAN detects. The rover has a soil scoop and can also dig with its wheels. Its robotic arm can put samples into instruments inside the rover for thorough analyses of ingredients. Rock formations that Curiosity's cameras view at the surface can be traced underground with DAN, enhancing the ability of scientists to understand the geology.

The neutron detectors on Odyssey rely on galactic cosmic rays hitting Mars as a source of neutrons. DAN can work in a passive mode relying on cosmic rays, but it also has its own pulsing neutron generator for an active mode of shooting high-energy neutrons into the ground. In active mode, it is sensitive enough to detect water content as low as one-tenth of one percent in the ground beneath the rover. 

The neutron generator is mounted on Curiosity's right hip. A module with two neutron detectors is mounted on the left hip. With pulses lasting about one microsecond and repeated as frequently as 10 times per second, key measurements by the detectors are the flux rate and delay time of moderated neutrons with different energy levels returning from the ground. The generator will be able to emit a total of about 10 million pulses during the mission, with about 10 million neutrons at each pulse.

"We have a fixed number of about 10 million shots, so one major challenge is to determine our strategy for how we will use them," said Maxim Litvak, leading scientist of the DAN investigation from the Space Research Institute.

Operational planning anticipates using DAN during short pauses in drives and while the rover is parked. It will check for any changes or trends in subsurface hydrogen content, from place to place along the traverse. Because there is a low possibility for underground water ice at Curiosity's Gale crater landing site, the most likely form of hydrogen in the ground of the landing area is hydrated minerals. These are minerals with water molecules or hydroxyl ions bound into the crystalline structure of the mineral. They can tenaciously retain water from a wetter past when all free water has gone.

"We want a better understanding of where the water has gone," said Alberto Behar, DAN investigation scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "DAN fits right into the follow-the-water strategy for studying Mars."

Mars Science Laboratory Project Scientist John Grotzinger of the California Institute of Technology in Pasadena said, "DAN will provide the ability to detect hydrated minerals or water ice in the shallow subsurface, which provides immediate clues as to how the geology of the subsurface might guide exploration of the surface.

In addition, DAN can tell us how the shallow subsurface may differ from what the rover sees at the surface. None of our other instruments have the ability to do this. DAN measurements will tell us about the habitability potential of subsurface rocks and soils — whether they contain water — and as we drive along, DAN may help us understand what kinds of rocks are under the soils we drive across."

6a00d8341bf7f753ef01543242e2e1970c.jpgIn an earlier study, researchers led by Brown graduate student Bethany Ehlmann report that ancient rivers ferried clay-like minerals (shown in green) into an ancient lake shown in this color-enhanced image of the delta in Jezero crater, a past lake on Mars. The clays then were trapped, meaning they could store past life. 

Ehlmann said scientists cannot determine whether the river flow was sporadic or sustained, but they do know it was intense and involved a lot of water.“So not only was water active in this region to weather the rocks, but there was enough of it to run through the beds, transport the clays and run into the lake and form the delta,” said Ehlmann. 

The deltas appear to be excellent candidates for finding stored organic matter, Ehlmann said, because the clays brought in from the watershed and deposited in the lake would have trapped any organisms, leaving in essence a cemetery of microbes.

“If any microorganisms existed on ancient Mars, the watershed would have been a great place to live,” Ehlmann said.

Images taken from the HiRISE orbiter above, three hundred kilometers above the Martian surface (a tad closer than the original millions of miles). show unmistakable paleoshorelines, series of strandlines defining a four-hundred meter deep lake extending over thirty square kilometers.  The shorelines are a particularly exciting place as land-water borders are among the most ecologically active regions on any planet – and the best at recording how that happened.  Fossils and chemical evidence of organisms can be buried in the sediments, and now we know where to look on Mars.

The discovery of the ex-lake, which evaporated during one of Mars' massive environmental changes, has massive implications just by existing – but it's more awesome than that.  The scanned shoreline is already an excellent contestant for the next "Where do we want to land on Mars?" competition so watch that sedimentary-space to see what happens.

"Most of the research on Mars has focused on its early history and the recent past. Scientists had largely overlooked the Hesperian Epoch as it was thought that Mars was then a frozen wasteland. Excitingly, our study now shows that this middle period in Mars' history was much more dynamic than we previously thought," said Nicholas Warner, Department of Earth Science and Engineering at Imperial College London who along with colleagues  suggests that during the Hesperian Epoch, approximately 3 billion years ago, Mars had lakes made of melted ice, each around 20km wide, along parts of the equator.

Earlier research had suggested that Mars had a warm and wet early history but that between 4 billion and 3.8 billion years ago, before the Hesperian Epoch, the planet lost most of its atmosphere and became cold and dry.

Researchers analyzed detailed images from NASA's Mars Reconnaissance Orbiter, which is currently circling the red planet, and concluded that there were later episodes where Mars experienced warm and wet periods.

The researchers say that there may have been increased volcanic activity, meteorite impacts or shifts in Mars' orbit during this period to warm Mars' atmosphere enough to melt the ice. This would have created gases that thickened the atmosphere for a temporary period, trapping more sunlight and making it warm enough for liquid water to be sustained.

The team used the images from the Mars Reconnaissance Orbiter to analyse several flat-floored depressions located above Ares Vallis, which is a giant gorge that runs 2,000 km across the equator of Mars.

Scientists have previously been unable to explain how these depressions formed, but believed that the depressions may have been created by a process known as sublimation, where ice changes directly from its solid state into a gas without becoming liquid water. The loss of ice would have created cavities between the soil particles, which would have caused the ground to collapse into a depression.

In another recent study, the researchers analysed the depressions and discovered a series of small sinuous channels that connected them together. The researchers say these channels could only be formed by running water, and not by ice turning directly into gas.

The scientists were able to lend further weight to their conclusions by comparing the Mars images to images of thermokarst landscapes that are found on Earth today, in places such as Siberia and Alaska. Thermokarst landscapes are areas where permafrost is melting, creating lakes that are interconnected by the same type of drainage channels found on Mars.

The team believes the melting ice would have created lakes and that a rise in water levels may have caused some of the lakes to burst their banks, which enabled water to carve a pathway through the frozen ground from the higher lakes and drain into the lower lying lakes, creating permanent channels between them.

"We can now model the 3D shape of Mars' surface down to sub-metre resolution, at least as good as any commercial satellite orbiting the Earth. This allows us to test our hypotheses in a much more rigorous manner than ever before," said Professor Jan-Peter Muller, Mullard Space Science Laboratory, Department of Space Climate Physics at University College London, was responsible for mapping the 3D shape of the surface of Mars. 

The researchers determined the age of the lakes by counting crater impacts, a method originally developed by NASA scientists to determine the age of geological features on the moon. More craters around a geological feature indicate that an area is older than a region with fewer meteorite impacts.

In the study, the scientists counted more than 35,000 crater impacts in the region around the lakes, and determined that the lakes formed approximately three billion years ago. The scientists are unsure how long the warm and wet periods lasted during the Hesperian epoch or how long the lakes sustained liquid water in them.

The researchers say their study may have implications for astrobiologists who are looking for evidence of life on Mars. The team say these lake beds indicate regions on the planet where it could have been warm and wet, potentially creating habitats that may have once been suitable for microbial life. The team say these areas may be good targets for future robotic missions.

The next step will be to survey other areas along the equator of Mars so that they can ascertain how widespread these lakes were during the Hesperian Epoch. The team will focus their surveys on a region at the mouth of Ares Vallis called Chryse Planitia, where preliminary surveys of satellite images have suggested that this area may have also supported lakes.

 

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The Daily Galaxy via Imperial College London, eurekalert.org , NASA/JPL,  Brown University , space.com

Image Credit:  NASA/JPL, Goudge, T.A., Head, J.W., Mustard, J.F. and Fassett, C.I./MOLA/NASA 

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