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Walking on Water: Man on Cydonia
...
Thanks for those last few fascinating and excellent posts on Water.
Some day it won't be such a conundrum of anomalous and elusive character to human science.

Applause
...
Reply
Each anomaly revealed is occulted ANU!

Doh

...Like digging a hole in water...


Scientists find seismic imaging is blind to water
March 14, 2018, Massachusetts Institute of Technology


[Image: scientistsfi.gif]
MIT scientists find seismic imaging is blind to water, which may help researchers reinterpret structures within the Earth, including at mid-ocean ridges, where it was thought that magma, welling up from the interior, contained trace amounts …more
When an earthquake strikes, nearby seismometers pick up its vibrations in the form of seismic waves. In addition to revealing the epicenter of a quake, seismic waves can give scientists a way to map the interior structures of the Earth, much like a CT scan images the body.



By measuring the velocity at which seismic waves travel at various depths, scientists can determine the types of rocks and other materials that lie beneath the Earth's surface. The accuracy of such seismic maps depends on scientists' understanding of how various materials affect seismic waves' speeds.

Now researchers at MIT and the Australian National University have found that seismic waves are essentially blind to a very common substance found throughout the Earth's interior: water.

Their findings, published today in the journal Nature, go against a general assumption that seismic imaging can pick up signs of water deep within the Earth's upper mantle. In fact, the team found that even trace amounts of water have no effect on the speed at which seismic waves travel.

The results may help scientists reinterpret seismic maps of the Earth's interior. For instance, in places such as midocean ridges, magma from deep within the Earth erupts through massive cracks in the seafloor, spreading away from the ridge and eventually solidifying as new oceanic crust.

The process of melting at tens of kilometers below the surface removes tiny amounts of water that are found in rocks at greater depth. Scientists have thought that seismic images showed this "wet-dry" transition, corresponding to the transition from rigid tectonic plates to deformable mantle beneath. However, the team's findings suggest that seismic imaging may be picking up signs of not water, but rather, melt - tiny pockets of molten rock.

"If we see very strong variations [in seismic velocities], it's more likely that they're due to melt," says Ulrich Faul, a research scientist in MIT's Department of Earth, Atmospheric, and Planetary Sciences. "Water, based on these experiments, is no longer a major player in that sense. This will shift how we interpret images of the interior of the Earth."

Faul's co-authors are lead author Christopher Cline, along with Emmanuel David, Andrew Berry, and Ian Jackson, of the Australian National University.

A seismic twist

Faul, Cline, and their colleagues originally set out to determine exactly how water affects seismic wave speeds. They assumed, as most researchers have, that seismic imaging can "see" water, in the form of hydroxyl groups within individual mineral grains in rocks, and as molecular-scale pockets of water trapped between these grains. Water, even in tiny amounts, has been known to weaken rocks deep in the Earth's interior.

 

"It was known that water has a strong effect in very small quantities on the properties of rocks," Faul says. "From there, the inference was that water also affects seismic wave speeds substantially."

To measure the extent to which water affects seismic wave speeds, the team produced different samples of olivine - a mineral that constitutes the majority of Earth's upper mantle and determines its properties. They trapped various amounts of water within each sample, and then placed the samples one at a time in a machine engineered to slowly twist a rock, similar to twisting a rubber band. The experiments were done in a furnace at high pressures and temperatures, in order to simulate conditions deep within the Earth.

"We twist the sample at one end and measure the magnitude and time delay of the resulting strain at the other end," Faul says. "This simulates propagation of seismic waves through the Earth. The magnitude of this strain is similar to the width of a thin human hair - not very easy to measure at a pressure of 2,000 times atmospheric pressure and a temperature that approaches the melting temperature of steel."

The team expected to find a correlation between the amount of water in a given sample and the speed at which seismic waves would propagate through that sample. When the initial samples did not show the anticipated behavior, the researchers modified the composition and measured again, but they kept getting the same negative result. Eventually it became inescapable that the original hypothesis was incorrect.

"From our [twisting] measurements, the rocks behaved as if they were dry, even though we could clearly analyze the water in there," Faul says. "At that point, we knew water makes no difference."

A rock, encased

Another unexpected outcome of the experiments was that seismic wave velocity appeared to depend on a rock's oxidation state. All rocks on Earth contain certain amounts of iron, at various states of oxidation, just as metallic iron on a car can rust when exposed to a certain amount of oxygen. The researchers found, almost unintentionally, that the oxidation of iron in olivine affects the way seismic waves travel through the rock.

Cline and Faul came to this conclusion after having to reconfigure their experimental setup. To carry out their experiments, the team typically encases each rock sample in a cylinder made from nickel and iron. However, in measuring each sample's water content in this cylinder, they found that hydrogen atoms in water tended to escape out of the rock, through the metal casing. To contain hydrogen, they switched their casing to one made from platinum.

To their surprise they found that the type of metal surrounding the samples affected their seismic properties. Separate experiments showed that what in fact changed was the amount of Fe3+ in olivine. Normally the oxidation state of iron in olivine is 2+. As it turns out, the presence of Fe3+ produces imperfections which affect seismic wave speeds.

Faul says that the group's findings suggest that seismic waves may be used to map levels of oxidation, such as at subduction zones - regions in the Earth where oceanic plates sink down into the mantle. Based on their results, however, seismic imaging cannot be used to image the distribution of water in the Earth's interior. What some scientists interpreted as water may in fact be melt - an insight that may change our understanding of how the Earth shifts its tectonic plates over time.

"An underlying question is what lubricates tectonic plates on Earth," Faul says. "Our work points toward the importance of small amounts of melt at the base of tectonic plates, rather than a wet mantle beneath dry plates. Overall these results may help to illuminate volatile cycling between the interior and the surface of the Earth."

[Image: 1x1.gif] Explore further: Mysterious deep-Earth seismic signature explained

More information: Redox-influenced seismic properties of upper-mantle olivine, Nature (2018). nature.com/articles/doi:10.1038/nature25764


Journal reference: Nature [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: Massachusetts Institute of Technology


Read more at: https://phys.org/news/2018-03-scientists...g.html#jCp


Wacky World of Water. Pennywise
Along the vines of the Vineyard.
With a forked tongue the snake singsss...
Reply
(03-13-2018, 12:13 AM)Vianova Wrote: ...
Thanks for those last few fascinating and excellent posts on Water.
Some day it won't be such a conundrum of anomalous and elusive character to human science.

Applause
...

Predicting a new phase of superionic ice

March 15, 2018, US Department of Energy


[Image: 3-predictingan.jpg]
Unlike Earth, which has two magnetic poles, ice giants such as Neptune (pictured) can have many local magnetic poles, which could be due to superionic ice and ionic water in the mantle of these planets. Credit: US Department of Energy

Scientists predicted a new phase of superionic ice, a special form of ice that could exist on Uranus, Neptune, and exoplanets. This new type of ice, called P21/c-SI phase, occurs at pressures greater than those found inside the giant ice planets of our solar system. The Princeton University team made this discovery using resources at the National Energy Research Scientific Computing Center (NERSC).



The theoretical simulations conducted at NERSC let the team model states of superionic ice that would be difficult to study experimentally. They simulated pressures beyond the highest possible pressures currently attainable in the laboratory. The simulations predict specific characteristics for this new type of ice, which could be used as signatures of superionic ice. The signature could someday be used by planetary scientists to observe superionic ice in our solar system or beyond.

Possibly residing on ice-rich planets in our solar system and beyond, superionic ice is an exotic type of ice that exists at high temperature and high pressure. In superionic ice, the water molecules dissociate into charged atoms (ions), with the oxygen ions locked in a solid lattice. The researchers from Princeton University conducted a comprehensive study on the different phases that superionic ice can undergo, looking at how the oxygen lattice changed and the liquid hydrogen moved. They calculated the ionic conductivity and hydrogen diffusivity of each phase. They found that the ionic conductivity increases dramatically when the ice changes from the solid phase to the superionic phase.

The change of conductivity is either gradual or abrupt depending on the superionic phase. Abrupt and gradual changes of conductivity are also observed in materials that can be superionic at atmospheric pressure. For example, an abrupt change of conductivity is observed in silver iodide (AgI) while a gradual conductivity change is observed in lead disulfide (PbS2). What is unusual about superionic ice is that these two types of conductivity changes are observed in the same material at different thermodynamic conditions. The Princeton University researchers simulated what would happen if the superionic form was put under extreme pressures, from 280 GPa to 1.3 TPa. They discovered the ice has competing phases within a close-packed oxygen lattice. As the pressure climbs, the close-packed structure becomes unstable. The lattice morphs into a new unusual phase, which is associated with a gradual change in ionic conductivity. The team also found that the higher pressure lowers the temperature necessary for the ice to transition to superionic phases.

[Image: 1x1.gif] Explore further: Scientists predict cool new phase of superionic ice

More information: Jiming Sun et al. The phase diagram of high-pressure superionic ice, Nature Communications (2015). DOI: 10.1038/ncomms9156


Journal reference: Nature Communications [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: US Department of Energy


Read more at: https://phys.org/news/2018-03-phase-supe...e.html#jCp


Water actually getz even moreso anomalous because it physically behaves differently wherever it is found or bound.
Itza same  Sheep difference no matter wich world you look at.
Along the vines of the Vineyard.
With a forked tongue the snake singsss...
Reply
Mars' oceans formed early, possibly aided by massive volcanic eruptions
March 19, 2018, University of California - Berkeley


[Image: marsoceansfo.jpg]
The early ocean known as Arabia (left, blue) would have looked like this when it formed 4 billion years ago on Mars, while the Deuteronilus ocean, about 3.6 billion years old, had a smaller shoreline. Both coexisted with the massive volcanic province Tharsis, located on the unseen side of the planet, which may have helped support the existence of liquid water. The water is now gone, perhaps frozen underground and partially lost to space, while the ancient seabed is known as the northern plains. Credit: Robert Citron images, UC Berkeley

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A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million years earlier and were not as deep as once thought.



The proposal by geophysicists at the University of California, Berkeley, links the existence of oceans early in Mars history to the rise of the solar system's largest volcanic system, Tharsis, and highlights the key role played by global warming in allowing
liquid water to exist on Mars.

"Volcanoes may be important in creating the conditions for Mars to be wet," said Michael Manga, a UC Berkeley professor of earth and planetary science and senior author of a paper appearing in Nature this week and posted online March 19.

Those claiming that Mars never had oceans of liquid water often point to the fact that estimates of the size of the oceans don't jibe with estimates of how much water could be hidden today as permafrost underground and how much could have escaped into space. These are the main options, given that the polar ice caps don't contain enough water to fill an ocean.

The new model proposes that the oceans formed before or at the same time as Mars' largest volcanic feature, Tharsis, instead of after Tharsis formed 3.7 billion years ago. Because Tharsis was smaller at that time, it did not distort the planet as much as it did later, in particular the plains that cover most of the northern hemisphere and are the presumed ancient seabed. The absence of crustal deformation from Tharsis means the seas would have been shallower, holding about half the water of earlier estimates.

"The assumption was that Tharsis formed quickly and early, rather than gradually, and that the oceans came later," Manga said. "We're saying that the oceans predate and accompany the lava outpourings that made Tharsis."

It's likely, he added, that Tharsis spewed gases into the atmosphere that created a global warming or greenhouse effect that allowed liquid water to exist on the planet, and also that volcanic eruptions created channels that allowed underground water to reach the surface and fill the northern plains.

 

Following the shorelines

The model also counters another argument against oceans: that the proposed shorelines are very irregular, varying in height by as much as a kilometer, when they should be level, like shorelines on Earth.

This irregularity could be explained if the first ocean, called Arabia, started forming about 4 billion years ago and existed, if intermittently, during as much as the first 20 percent of Tharsis's growth. The growing volcano would have depressed the land and deformed the shoreline over time, which could explain the irregular heights of the Arabia shoreline.

Similarly, the irregular shoreline of a subsequent ocean, called Deuteronilus, could be explained if it formed during the last 17 percent of Tharsis's growth, about 3.6 billion years ago.

"These shorelines could have been emplaced by a large body of liquid water that existed before and during the emplacement of Tharsis, instead of afterwards," said first author Robert Citron, a UC Berkeley graduate student. Citron will present a paper about the new analysis on March 20 at the annual Lunar and Planetary Science conference in Texas.

Tharsis, now a 5,000-kilometer-wide eruptive complex, contains some of the biggest volcanoes in the solar system and dominates the topography of Mars. Earth, twice the diameter and 10 times more massive than Mars, has no equivalent dominating feature. Tharsis's bulk creates a bulge on the opposite side of the planet and a depression halfway between. This explains why estimates of the volume of water the northern plains could hold based on today's topography are twice what the new study estimates based on the topography 4 billion years ago.

New hypothesis supplants old
Quote:.
Quote: Wrote:InSight stands for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport.
You can't really do SEISMIC  [Image: doh.gif] if you don't understand the constituent properties of the substances and materials inside the core or mantle.

Rare metals on Mars and Earth implicate colossal impacts
March 16, 2018 by Amanda Doyle, Astrobio.net


Geodesy and Heat Transport.


Manga, who models the internal heat flow of Mars, such as the rising plumes of molten rock that erupt into volcanoes at the surface, tried to explain the irregular shorelines of the plains of Mars 11 years ago with another theory
. He and former graduate student Taylor Perron suggested that Tharsis, which was then thought to have originated at far northern latitudes, was so massive that it caused the spin axis of Mars to move several thousand miles south, throwing off the shorelines.

Since then, however, others have shown that Tharsis originated only about(~19.5) 20 degrees above the equator, nixing that theory. But Manga and Citron came up with another idea,  Doh that the shorelines could have been etched as Tharsis was growing, not afterward.
The new theory also can account for the cutting of valley networks by flowing water at around the same time.

"This is a hypothesis," Manga emphasized. "But scientists can do more precise dating of Tharsis and the shorelines to see if it holds up."

NASA's next Mars lander, the InSight mission (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport), could help answer the question. Scheduled for launch in May, it will place a seismometer on the surface to probe the interior and perhaps find frozen remnants of that ancient ocean, or even liquid water.

 Explore further: Mars upside down

More information: Robert I. Citron et al, Timing of oceans on Mars from shoreline deformation, Nature (2018). DOI: 10.1038/nature26144


Journal reference: Nature
Provided by: University of California - Berkeley


Read more at: https://phys.org/news/2018-03-mars-ocean...d.html#jCp



Naughty Manga.

This Negates That  Arrow  #6 Friday, March 16th, 2018, 09:20 pm

----------------------------------------------------------------------------------
This new model should be considered when projecting commences.

They've got about ~50 days to update any software if necessary.
Quote: Wrote:InSight stands for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport.
You can't really do SEISMIC  [Image: doh.gif] if you don't understand the constituent properties of the substances and materials inside the core or mantle.

Rare metals on Mars and Earth implicate colossal impacts
March 16, 2018 by Amanda Doyle, Astrobio.net


[Image: raremetalson.jpg]
The surface features of the northern and southern hemispheres of Mars are very different. In this topographic map, the northern hemisphere (shown in blue) is mostly smooth lowlands and has experienced extensive volcanism. The southern hemisphere (in orange) has an older, cratered highland surface. This dichotomy could have been caused by a giant impact. Credit: University of Arizona/LPL/SwRI
New research has revealed that a giant impact on Mars more than four billion years ago would explain the unusual amount of "iron loving" elements in the Red Planet.

Planets form as small dust grains stick together and agglomerate with other grains, leading to bigger bodies termed "planetesimals." These planetesimals continue to collide with each other and are either ejected from the solar system, gobbled up by the sun, or form a planet. This is not the end of the story, as planets continue to accrete material well after they have formed. This process is known as late accretion, and it occurs as leftover fragments of planet formation rain down on the young planets.

Planetary scientist Ramon Brasser of the Tokyo Institute of Technology and geologist Stephen Mojzsis of the University of Colorado, Boulder took a closer look at a colossal impact during Mars' late accretion that could explain the unusual amount of rare metallic elements in Mars' mantle, which is the layer below the planet's crust. Their recently published paper, "A colossal impact enriched Mars' mantle with noble metals," appeared in the journal Geophysical Research Letters.

When proto-planets accrete enough material, metals such as iron and nickel begin to separate and sink to form the core. This explains why Earth's core is mainly composed of iron, and it is expected that elements that readily bond with iron should also mainly exist in the core. Examples of such 'iron loving' elements, known as siderophiles, are gold, platinum and iridium, to name a few. Just like Mars, however, there are more siderophiles in the Earth's mantle than would be expected by the process of core formation.

"High pressure experiments indicate that these metals should not be in the mantle. These metals don't like being dissolved in silicate and instead they prefer to sink through the mantle into the Earth's core," Brasser tells Astrobiology Magazine. "The fact that we do have them at all means that they must have arrived after the core and the mantle separated, when it became much more difficult for these metals to reach the core."

A 2016 paper by Brasser and colleagues conclusively showed that a giant impact is the best explanation for Earth's high siderophile element abundance.

 

The amount of siderophiles accumulated during late accretion should be proportional to the 'gravitational cross section' of the planet. This cross section is effectively the cross hairs that an impactor 'sees' as it approaches a target planet. The gravitational cross section extends beyond the planet itself, as the world's gravity will direct an object towards it even when the object was not on a direct collision course. This process is called gravitational focusing.

The earlier paper showed that Earth has more siderophiles in the mantle than it should, even according to the gravitational cross section theory. The scientists explained this by showing that an impact of a lunar-sized body on the Earth (in addition to the event that formed the moon) would have enriched the mantle with enough siderophiles to explain the current value.

An early giant impact

Analysis of Martian meteorites show that Mars accreted another 0.8 percent by mass (weight percent, or wt percent) of material via late accretion. In the new paper, Brasser and Mojzsis show that for Mars to have amended its mass by about 0.8 wt percent in a single impact event required a body at least 1,200 kilometers in diameter.

They further argue that such an impact ought to have occurred some time between 4.5 and 4.4 billion years ago. Studies of zircon crystals in ancient Martian meteorites can be used to date the formation of the Martian crust to before 4.4 billion years ago. As such, a giant impact should have caused widespread crustal melting and such a catastrophic event must have occurred before the evidence for the oldest crust. If the impact occurred as early in the planet's history as 4.5 billion years ago, then the siderophiles should have been stripped away during core formation. This history provides firm bookend constraints on when the impact happened.

Understanding late accretion is not just important for explaining the siderophile abundance, but also for placing an upper limit on the age of Earth's biosphere.

"During each impact, a small bit of Earth's crust is locally melted," says Brasser. "When the accretion is very intense, almost all of Earth's crust is molten. As the accretion intensity decreases, the amount of crustal melting also decreases. We argue that the earliest time you could form a biosphere is when the accretion is low enough so that less than 50 percent of the crust is molten at any given time."

The surface of Mars also has an unusual dichotomy, which could be explained by a giant impact. The southern hemisphere exists as an ancient cratered terrain, and the northern hemisphere appears younger and smoother and was influenced by extensive volcanism. A giant impact might also have created the Martian moons, Deimos and Phobos, although an alternative theory is that the highly porous Phobos could be a captured asteroid.

 Explore further: Collisions after moon formation remodeled early Earth

More information: A colossal impact enriched Mars' mantle with noble metals, arxiv.org/abs/1706.02014


Journal reference: Geophysical Research Letters
Source:: [url=https://phys.org/partners/astrobio-net/]Astrobio.net


Read more at: https://phys.org/news/2018-03-rare-metal...e.html#jCp






Astrophysics > Earth and Planetary Astrophysics
A colossal impact enriched Mars' mantle with noble metals
R. Brasser, S. J. Mojzsis
(Submitted on 7 Jun 2017)
Quote: Wrote:Once the terrestrial planets had mostly completed their assembly, bombardment continued by planetesimals left-over from accretion. Highly siderophile element (HSE) abundances in Mars' mantle imply its late accretion supplement was 0.8 wt.%; Earth and the Moon obtained an additional 0.7 wt.% and 0.02 wt.%, respectively. The disproportionately high Earth/Moon accretion ratio is explicable by stochastic addition of a few remaining Ceres-sized bodies that preferentially targeted Earth. Here we show that Mars' late accretion budget also requires a colossal impact, a plausible visible remnant of which is the hemispheric dichotomy. The addition of sufficient HSEs to the martian mantle entails an impactor of at least 1200 km in diameter to have struck Mars before ca. 4430 Ma, by which time crust formation was well underway. Thus, the dichotomy could be one of the oldest geophysical features of the martian crust. Ejected debris could be the source material for its satellites.
Comments:
Accepted for publication in Geophysical Research Letters
Subjects:
Earth and Planetary Astrophysics (astro-ph.EP)
DOI:
10.1002/2017GL074002
Cite as:
arXiv:1706.02014 [astro-ph.EP]
 
(or arXiv:1706.02014v1 [astro-ph.EP] for this version)
Submission history
From: Ramon Brasser [view email]
[v1] Wed, 7 Jun 2017 00:38:46 GMT (403kb)
Along the vines of the Vineyard.
With a forked tongue the snake singsss...
Reply
(03-13-2018, 12:13 AM)Vianova Wrote: ...
Thanks for those last few fascinating and excellent posts on Water.
Some day it won't be such a conundrum of anomalous and elusive character to human science.
 
...

Sum-Day Arrow

 Understanding the strange behavior of water

March 27, 2018, University of Bristol


[Image: 8-understandin.jpg]
A clathrate ice, with oxygens represented as spheres, and hydrogen-bonds as lines. The work has shown how complex crystalline structures emerge as a result of water's interactions. Credit: University of Bristol
The properties of water have fascinated scientists for centuries, but yet its unique behaviour remains a mystery.

Published this week in the journal Proceedings of the National Academy of Sciences, a collaboration between the Universities of Bristol and Tokyo has attempted a novel route to understand what makes a liquid behave like water.

When compared to an ordinary liquid, water displays a vast array of anomalies. Common examples include the fact that liquid water expands on cooling below 4 C, which is responsible for lakes freezing from the top rather than the bottom.

In addition, the fact that water becomes less viscous when compressed, or its unusually high surface tension, allows insects to walk on water's surface.

These and many other anomalies are of fundamental importance in countless natural and technological processes, such as the Earth's climate, and the possibility of life itself. From an anthropic viewpoint, it is like the water molecule was fine-tuned to have such unique properties.

Starting from the observation that the properties of water seem to appear fine-tuned, a collaboration between Dr John Russo from the University of Bristol's School of Mathematics and Professor Hajime Tanaka from the University of Tokyo, harnessed the power of powerful supercomputers, using computational models to slowly "untune" water's interactions.

This showed how the anomalous properties of water can be changed and eventually reduced to those of a simple liquid. For example, instead of floating on water, the density of ice can be changed continuously until it sinks, and the same can be done with all water anomalies.

Dr Russo said: "With this procedure, we have found that what makes water behave anomalously is the presence of a particular arrangement of the water's molecules, such as the tetrahedral arrangement, where a water molecule is hydrogen-bonded to four molecules located on the vertices of a tetrahedron.

"Four of such tetrahedral arrangements can organise themselves in such a way that they share a common water molecule at the centre without overlapping.

"It is the presence of this highly ordered arrangement of water molecules, mixed with other disordered arrangements that gives water its peculiar properties.

"We think this work provides a simple explanation of the anomalies and highlights the exceptional nature of water, which makes it so special compared with any other substance."

[Image: 1x1.gif] Explore further: Tetrahedrality is key to the uniqueness of water

More information: John Russo et al, Water-like anomalies as a function of tetrahedrality, Proceedings of the National Academy of Sciences (2018). DOI: 10.1073/pnas.1722339115


Journal reference: Proceedings of the National Academy of Sciences [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: University of Bristol


Read more at: https://phys.org/news/2018-03-strange-behavior.html#jCp



Sum-Day Arrow

Tetrahedrality is key to the uniqueness of water

March 27, 2018, University of Tokyo


[Image: tetrahedrali.jpg]
An image of the clathrate structure (Si34) of water-type liquid formed at a negative pressure (left) and the phase diagram as a function of the strength of tetrahedrality λ and pressure P. Credit: 2018 Hajime Tanaka, Institute of Industrial Science, The University of Tokyo
A Japan-based research team has studied the anomalous behavior of tetrahedral liquids such as water. Via computer simulation, they calculated the phase diagrams of a range of model liquids. Varying a parameter called lambda (λ), which controls the amount of tetrahedral structure in the liquid, they found that liquids with greater λ showed more anomalies, such as low-temperature expansion. Water's value of λ maximizes the effect of tetrahedrality, hence its especially unusual properties.



Water holds a special place among liquids for its unusual properties, and remains poorly understood. For example, it expands just upon the freezing to ice, and becomes less viscous under compression, around atmospheric pressure. Rationalizing these oddities is a major challenge for physics and chemistry. Recent research led by the University of Tokyo's Institute of Industrial Science (IIS) suggests they result from the degree of structural ordering in the fluid.

Water belongs to a class of liquids whose particles form local tetrahedral structures. The tetrahedrality of water is a consequence of hydrogen bonds between molecules, which are constrained to fixed directions. In a study in the Proceedings of the National Academy of Sciences (PNAS), the researchers investigated why the physical properties of water as expressed by its phase diagram are so remarkable, even compared with other tetrahedral liquids, such as silicon and carbon.

Tetrahedral liquids are often simulated by an energy potential called the SW model. The liquid is assumed to contain two phases in thermodynamic equilibrium—a disordered state that has high rotational symmetry, and a tetrahedrally ordered state that does not. Despite its simplicity, the model accurately predicts anomalous liquid behaviors. The two-state property is controlled by the parameter lambda (λ), which describes the relative strength of pairwise and three-body intermolecular interactions. The higher λ is, the degree of tetrahedral order increases.

"We realized that λ, which is rather large for water, was key to the uniqueness of these liquids," study co-lead author John Russo says. "Effectively, λ controls the degree of tetrahedrality: as λ increases, tetrahedral shells forming around each molecule become energetically more stable. Hence, these shells overcome the unfavorable loss of entropy that accompanies the creation of order." The local tetrahedra resemble solid-state structures, which is why high-λ liquids crystallize more easily.

By continuously adjusting λ, they simulated a set of phase diagrams to model what happens when a "simple" liquid becomes progressively more water-like. With increasing λ, the various thermodynamic and dynamic anomalies of tetrahedral liquids—such as expansion at low temperature and the breaking of the standard Arrhenius law for diffusion —- became more pronounced.

However, it was not as simple as "more tetrahedra equals weirder behavior." The influence of tetrahedrality was maximized for water, which has λ = 23.15. Above here, the behavior of density as a function of temperature approached normal again, because the difference in volume between ordered and disordered states began to drop. Thus, water has an exquisitely fine-tuned or "Goldilocks" value of λ that lets it shift easily between order and randomness. This gives it high structural flexibility in response to changing temperature or pressure, which is the origin of its unique behavior.

"Linking observable properties, such as viscosity to microscopic structures, is what physical chemistry is all about," co-lead author Hajime Tanaka says. "Water, the most abundant and yet most unusual substance on earth, has long been the final frontier in this respect. We were delighted that a simple, well-known model can fully explain the strangeness of water, which arises from the delicate balance between order and disorder in the liquid."

[Image: 1x1.gif] Explore further: Breaking local symmetry—why water freezes but silica forms a glass

More information: John Russo et al, Water-like anomalies as a function of tetrahedrality, Proceedings of the National Academy of Sciences (2018). DOI: 10.1073/pnas.1722339115


Journal reference: Proceedings of the National Academy of Sciences [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: University of Tokyo


Read more at: https://phys.org/news/2018-03-tetrahedra...s.html#jCp



Quote:Water-like anomalies as a function of tetrahedrality
John Russo, Kenji Akahane and Hajime Tanaka
PNAS March 26, 2018. 201722339; published ahead of print March 26, 2018. https://doi.org/10.1073/pnas.1722339115

  1. Edited by Pablo G. Debenedetti, Princeton University, Princeton, NJ, and approved February 27, 2018 (received for review December 21, 2017)
Significance
Water is the most common and yet least understood material on Earth. Despite its simplicity, water tends to form tetrahedral order locally by directional hydrogen bonding. This structuring is known to be responsible for a vast array of unusual properties, e.g., the density maximum at 4 °C, which play a fundamental role in countless natural and technological processes, with the Earth’s climate being one of the most important examples. By systematically tuning the degree of tetrahedrality, we succeed in continuously interpolating between water-like behavior and simple liquid-like behavior. Our approach reveals what physical factors make water so anomalous and special even compared with other tetrahedral liquids.
Abstract
Tetrahedral interactions describe the behavior of the most abundant and technologically important materials on Earth, such as water, silicon, carbon, germanium, and countless others. Despite their differences, these materials share unique common physical behaviors, such as liquid anomalies, open crystalline structures, and extremely poor glass-forming ability at ambient pressure. To reveal the physical origin of these anomalies and their link to the shape of the phase diagram, we systematically study the properties of the Stillinger–Weber potential as a function of the strength of the tetrahedral interaction λ
. We uncover a unique transition to a reentrant spinodal line at low values of λ, accompanied with a change in the dynamical behavior, from non-Arrhenius to Arrhenius. We then show that a two-state model can provide a comprehensive understanding on how the thermodynamic and dynamic anomalies of this important class of materials depend on the strength of the tetrahedral interaction. Our work establishes a deep link between the shape of the phase diagram and the thermodynamic and dynamic properties through local structural ordering in liquids and hints at why water is so special among all substances.


Tetrahedrality is key to the uniqueness of water

Sums up nicely.

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Hydrogen is part of water and quantum properties are in water. Arrow

Date:March 27, 2018Source:Carnegie Institution for ScienceSummary:A team of scientists now report unexpected quantum behavior of hydrogen molecules,
H2
, trapped within tiny cages made of organic molecules, demonstrating that the structure of the cage influences the behavior of the molecule imprisoned inside it. 


FULL STORY
Molecular prison forces diatomic inmates to cell floor
Organic prison too crowded for molecular inmates to move about freely

[Image: 180327110457_1_540x360.jpg]
Is it a UFO? No. It's the probability distribution of a rotating hydrogen molecule trapped inside an organic clathrate cage.
Credit: Illustration is courtesy of Tim Strobel

A team of scientists including Carnegie's Tim Strobel and Venkata Bhadram now report unexpected quantum behavior of hydrogen molecules, H2, trapped within tiny cages made of organic molecules, demonstrating that the structure of the cage influences the behavior of the molecule imprisoned inside it.

A detailed understanding of the physics of individual atoms interacting with each other at the microscopic level can lead to the discovery of novel emergent phenomena, help guide the synthesis of new materials, and even aid future drug development.
But at the atomic scale, the classical, so-called Newtonian, rules of physics you learned in school don't apply. In the arena of the ultra-small, different rules, governed by quantum mechanics, are needed to understand interactions between atoms where energy is discrete, or non-continuous, and where position is inherently uncertain.
The research team -- including Anibal Ramirez-Cuesta, Luke Daemen, and Yongqiang Cheng of Oak Ridge National Laboratory, as well as Timothy Jenkins and Craig Brown of the National Institute of Standards and Technology-used spectroscopic tools, including the state-of-the-art inelastic neutron spectrometer called VISION at the Spallation Neutron Source, to examine the atomic-level dynamics of a special kind of molecular structure called a clathrate.
Clathrates consist of a lattice structure that forms cages, trapping other types of molecules inside, like a molecular-scale prison. The clathrate the team studied, called ?-hydroquinone, consisted of cages made from organic molecules that trap H2. Only a single H2 molecule is present within each cage, so the quantum behavior of the isolated molecules could be examined in detail.
"Practical examples of isolated quantum-influenced particles that are trapped inside well-defined spaces provide the opportunity to probe dynamics under conditions that are approaching simulation-like perfection," Strobel explained.
The research team was able to observe how the hydrogen molecule rattled and rotated within the cage. Surprisingly, the observed rotational motion was unlike that of H2 trapped in related systems in which molecules can rotate almost freely in all directions.
"The behavior we observed here is similar to the behavior of H2 molecules that are adhering to a metal surface," Strobel explained. "It is the first time this behavior, known by physicists as a two-dimensional hindered rotor, has been observed for hydrogen trapped within a molecular clathrate."
It turns out that the local structure of the clathrate cage greatly influences the dynamics of H2, causing a preference for rotation in two dimensions despite the fact that there are no chemical bonds involved. In addition to the fundamental insights, this discovery could have important implications for the design of hydrogen storage materials that can trap H2 for energy and transportation applications.
This work was supported as part of the Energy Frontier Research in Extreme Environments (EFree) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science under Award No. DE-SC0001057. This research benefited from use of the VISION beamline (IPTS-16698) at ONRL's Spallation Neutron Source which is supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract No. DE-AC0500OR22725 with UT Battelle, LLC.

Story Source:
Materials provided by Carnegie Institution for Science. Note: Content may be edited for style and length.

Journal Reference:
  1. Timothy A. Strobel, Anibal J. Ramirez-Cuesta, Luke L. Daemen, Venkata S. Bhadram, Timothy A. Jenkins, Craig M. Brown, Yongqiang Cheng. Quantum Dynamics of H2 Trapped within Organic Clathrate Cages. Physical Review Letters, 2018; 120 (12) DOI: 10.1103/PhysRevLett.120.120402

Cite This Page: Carnegie Institution for Science. "Molecular prison forces diatomic inmates to cell floor: Organic prison too crowded for molecular inmates to move about freely." ScienceDaily. ScienceDaily, 27 March 2018. <www.sciencedaily.com/releases/2018/03/180327110457.htm>.
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Study suggests Earth's water was present before impact that caused creation of the moon
March 29, 2018 by Bob Yirka, Phys.org report


[Image: earthmoon.jpg]
This image shows the far side of the Moon, illuminated by the Sun. Credit: NASA
A team of researchers from the U.K., France and the U.S. has found evidence that suggests that most of the water on Earth was present before the impact that created the moon. In their paper published on the open access site Science Advances, the group describes their study and comparison of moon and Earth rocks, and what they found.

The prevailing theory regarding how the moon's origin is that a Mars-sized protoplanet slammed into protoplanetary Earth, and the ejected material coalesced to form the moon. The prevailing theory regarding how water came to exist on Earth is that most of it was delivered by asteroids and comets. In this new effort, the researchers present evidence that bolsters the first theory but conflicts strongly with the second.

The team studied both moon rocks brought back to Earth by the Apollo astronauts and volcanic rocks retrieved by others from the ocean floor. The researchers looked specifically at oxygen isotopes. Studying isotopes in rocks offers scientists a means for comparing material from different origins such as asteroids, planets or even comets—each tends to have its own unique composition signature.

The researchers report that oxygen isotopes from the moon and Earth are remarkably similar—they found just a three to four ppm difference between them. This finding bolsters the theory that the moon was formed from material from the Earth due to a collision. But it runs counter to the idea that water came from comets or asteroids, because if it had come from such sources, the isotopes would have differed from those found in rocks on the moon. Thus, most of the water that was present in the protoplanetary Earth likely survived the impact, suggesting it did not come from elsewhere.

The idea that water could survive such an impact has implications for the search for life beyond our solar system—exoplanets that are thought to have suffered collisions are typically removed from lists describing possible life-sustaining celestial bodies. Now, they may have to be included.

[Image: 1x1.gif] Explore further: Gallium in lunar samples explains loss of moon's easily vaporized elements

More information: Richard C. Greenwood et al. Oxygen isotopic evidence for accretion of Earth's water before a high-energy Moon-forming giant impact, Science Advances (2018). DOI: 10.1126/sciadv.aao5928

Abstract
The Earth-Moon system likely formed as a result of a collision between two large planetary objects. Debate about their relative masses, the impact energy involved, and the extent of isotopic homogenization continues. We present the results of a high-precision oxygen isotope study of an extensive suite of lunar and terrestrial samples. We demonstrate that lunar rocks and terrestrial basalts show a 3 to 4 ppm (parts per million), statistically resolvable, difference in Δ17O. Taking aubrite meteorites as a candidate impactor material, we show that the giant impact scenario involved nearly complete mixing between the target and impactor. Alternatively, the degree of similarity between the Δ17O values of the impactor and the proto-Earth must have been significantly closer than that between Earth and aubrites. If the Earth-Moon system evolved from an initially highly vaporized and isotopically homogenized state, as indicated by recent dynamical models, then the terrestrial basalt-lunar oxygen isotope difference detected by our study may be a reflection of post–giant impact additions to Earth. On the basis of this assumption, our data indicate that post–giant impact additions to Earth could have contributed between 5 and 30% of Earth's water, depending on global water estimates. Consequently, our data indicate that the bulk of Earth's water was accreted before the giant impact and not later, as often proposed.


Journal reference: Science Advances


Read more at: https://phys.org/news/2018-03-earth-impa...n.html#jCp
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(03-13-2018, 12:13 AM)Vianova Wrote: ...
Thanks for those last few fascinating and excellent posts on Water.
Some day it won't be such a conundrum of anomalous and elusive character to human science.

Applause
...

Unlocking the secrets of ice

April 9, 2018 by Bex Caygill, University College London


[Image: 5-unlockingthe.jpg]
Credit: Pixabay
The complex properties of water and ice are not well understood but a team from UCL and the ISIS Neutron and Muon Source have revealed new information about a phase of ice called ice II.



Given that water makes up 60% of our bodies and is one of the most abundant molecules in the universe, it's no wonder that water is known as the "matrix of life."

There are many different forms of ice – all of which vary significantly from the ice you'd find in your freezer. Ice takes on many different forms depending on the pressure at which it developed.

As water freezes its molecules rearrange themselves, and high pressure causes the molecules to rearrange in different ways than they normally would. The many distinct phases of ice can be summarised using a phase diagram, which shows the preferred physical states of matter at different temperatures and pressures.

Researchers from UCL and the Science and Technology Facilities Council (STFC) ISIS Neutron and Muon Source have utilised high pressure neutron diffraction to investigate the impact of ammonium fluoride impurities on water's phase diagram.

Their surprising results, published in Nature Physics, found the addition of this impurity caused a particular phase of ice, known as ice II, to completely disappear from water's phase diagram whereas the other phases were unaffected.

The many different phases of ice can be grouped into one of two types – hydrogen-ordered phases and hydrogen-disordered phases. In these different phases the orientation of water molecules is either firmly defined or disordered.

Ice II is a hydrogen-ordered phase of ice that forms under conditions of high pressure. Unlike other phases of ice, ice II remains thermodynamically stable and hydrogen-ordered up to very high temperatures and the origin of this anomalous result is not well understood.

Using neutron diffraction the group revealed the very special properties of ice II. The PEARL high pressure neutron diffractometer at ISIS Neutron and Muon Source is optimised for diffraction studies up to 20 GPa, though here samples were only exposed to 0.3 GPa. Even though this is well below the full capability of the instrument 0.3 GPa is still equivalent to 3 tonnes pressing down on a single fingernail.

 

For the neutron diffraction measurements ground ice samples were placed inside a titanium-zirconium can, which neutrons easily penetrate. The extreme pressure on PEARL was generated using a gas compressor filled with argon gas. PEARL allows in-situ pressure neutron diffraction measurements to take place, which were essential for this research.

"Without in-situ neutron diffraction we could not have performed this study. It was paramount to demonstrate that ice II has disappeared in the region of the phase diagram where it would normally exist," said Dr. Christoph G. Salzmann (UCL Chemistry).

In addition to collecting high pressure neutron diffraction data, researchers also utilised computational methods to gain very important insights. They found that doping ice II with small amounts of ammonium fluoride caused this particular phase of ice to disappear altogether, whereas the competing phases of ice were unaffected. This observation allowed researchers to infer important information on the highly unusual properties of ice II.

"Unlike the other phases, ice II is topologically constraint. This means that water molecules in ice II interact with each other over very long distances. In a sense, whatever happens to one water molecule in a crystal of ice II—the effect is "felt" by all other molecules. In our study, ice II experiences a disturbance by the ammonium fluoride which destabilises all of the ice II and makes it disappear," Dr. Salzmann added.

The knowledge of this effect will be of importance to any study where ice coexists with other materials in nature, for example on icy moons. In addition, the special properties of ice II provide a new explanation as to why the phase diagram of water displays so many anomalies, including liquid water. These findings may also open up studies into new phases of ice. If dopants have the ability to suppress certain phases of ice this suggests they may also be able to induce the formation of new phases of ice.

Interest in the "matrix of life," and its many phases of ice, certainly shows no sign of wavering. With high pressure neutron diffraction allowing the study of extreme pressure environments in a way that no other technique can, we are likely to see the team back at the facility in search of new phases of ice.

[Image: 1x1.gif] Explore further: Rapid decompression key to making low-density liquid water

More information: Jacob J. Shephard et al. Doping-induced disappearance of ice II from water's phase diagram, Nature Physics (2018). DOI: 10.1038/s41567-018-0094-z


Journal reference: Nature Physics [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: University College London


Read more at: https://phys.org/news/2018-04-secrets-ice.html#jCp
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Quote:"We saw these radar signatures telling us there's water, but we thought it was impossible that there could be liquid water underneath this ice, where it is below -10C."


Newly discovered salty subglacial lakes could help search for life in solar system
April 11, 2018, University of Alberta


[Image: 33-scientistsdi.jpg]
A cold and windy spring night on the vast landscape of Devon Ice Cap -- twosubglacial lakes are lurking 750 m below the surface. Credit: Anja Rutishauser

An analysis of radar data led scientists to an unexpected discovery of two lakes located beneath 550 to 750 metres of ice underneath the Devon Ice Cap, one of the largest ice caps in the Canadian Arctic. They are thought to be the first isolated hypersaline subglacial lakes in the world.



"We weren't looking for subglacial lakes. The ice is frozen to the ground underneath that part of the Devon Ice Cap, so we didn't expect to find liquid water," said Anja Rutishauser, PhD student at the University of Alberta, who made the discovery while studying airborne radar data acquired by NASA and The University of Texas Institute for Geophysics (UTIG) to describe the bedrock conditions underneath the Devon Ice Cap. Ice penetrating radar sounding measurements are based on electromagnetic waves that are sent through the ice and reflected back at contrasts in the subsurface materials, essentially allowing scientists to see through the ice.

"We saw these radar signatures telling us there's water, but we thought it was impossible that there could be liquid water underneath this ice, where it is below -10C."

While there are more than 400 known subglacial lakes in the world, concentrated primarily in Antarctica with a few in Greenland, these are the first found in the Canadian Arctic. And unlike all the others—which are believed to contain freshwater—these two appear to consist of hypersaline water. Rutishauser explained that the source of the salinity comes from salt-bearing geologic outcrops underneath the ice.

[Image: 32-scientistsdi.jpg]
In transit view during an aerogeophysical survey flight over Canadian Arcticice caps. Credit: Gregory Ng

Rutishauser collaborated with her PhD supervisor, UAlberta glaciologist Martin Sharp and University of Texas geophysicist Don Blankenship as well as other scientists from University of Texas at Austin, Montana State University, Stanford University, and the Scott Polar Research Institute to test her hypothesis. The bodies of water—roughly eight and five kilometres squared, respectively—exist at temperatures below freezing and are not connected to any marine water sources or surface meltwater inputs, but rather are hypersaline, containing water four to five times saltier than seawater, which allows the water to remain liquid at these cold temperatures.

These newly discovered lakes are a potential habitat for microbial life and may assist scientists in the search for life beyond earth. Though all subglacial lakes are good analogues for life beyond Earth, the hypersaline nature of the Devon lakes makes them particularly tantalizing analogues for ice-covered moons in our solar system.

 

"We think they can serve as a good analogue for Europa, one of Jupiter's icy moons, which has similar conditions of salty liquid water underneath—and maybe within—an ice shell," said Rutishauser.

[Image: 31-scientistsdi.jpg]
Pilots' view from the cockpit of a Kenn Borek Air Ltd. DC-3 aircraft duringan aerogeophysical survey flight over Canadian Arctic ice caps. Credit: Gregory Ng

"If there is microbial life in these lakes, it has likely been under the ice for at least 120,000 years, so it likely evolved in isolation. If we can collect a sample of the water, we may determine whether microbial life exists, how it evolved, and how it continues to live in this cold environment with no connection to the atmosphere."

Rutishauser believes that similar salty rock outcrops occur underneath other Canadian Arctic ice caps. "Although the Devon hypersaline subglacial lakes are very unique discoveries, we may find networks of brine-rich subglacial water systems elsewhere in the Canadian Arctic."

Rutishauser and her colleagues are now partnering with The W. Garfield Weston Foundation to undertake a more detailed airborne geophysical survey over the Devon Ice Cap this spring to derive more information about the lakes and their geological and hydrological contexts. For three generations, The W. Garfield Weston Foundation has pursued its mission to enhance and enrich the lives of Canadians. With a focus on medical research, the environment, and education, the Foundation aims to catalyze inquiry and innovation to bring about long-term change. As the Foundation marks its 60th anniversary, it continues to collaborate with a broad range of Canadian charities to further world-class research, explore new ideas, and create tangible benefits for the communities in which it works.

Following completion of her PhD with Sharp at the University of Alberta this summer, Rutishauser will start a postdoctoral fellowship in the fall at the University of Texas at Austin.

"Discovery of a hypersaline subglacial lake complex beneath Devon Ice Cap, Canadian Arctic" was published in the April 11 edition of Science Advances.

[Image: 1x1.gif] Explore further: Calm lakes on Titan could mean smooth landing for future space probes

More information: A. Rutishauser el al., "Discovery of a hypersaline subglacial lake complex beneath Devon Ice Cap, Canadian Arctic," Science Advances (2018). DOI: 10.1126/sciadv.aar4353 , advances.sciencemag.org/content/4/4/eaar4353


Journal reference: Science Advances [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: University of Alberta


Read more at: https://phys.org/news/2018-04-newly-salt...e.html#jCp





Mars Express v.2.0 LilD
April 11, 2018, European Space Agency


[Image: 3-marsexpressv.jpg]
Artist's impression of Mars Express. The background is based on an actual image of Mars taken by the spacecraft's high resolution stereo camera. Credit: Spacecraft: ESA/ATG medialab; Mars: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO
Every so often, your smartphone or tablet receives new software to improve its functionality and extend its life. Now, ESA's Mars Express is getting a fresh install, delivered across over 150 million km of space.



With nearly 15 years in orbit, Mars Express – one of the most successful interplanetary missions ever – is on track to keep gathering critical science data for many more years thanks to a fresh software installation developed by the mission teams at ESA.

The new software is designed to fix a problem that anyone still using a five-year-old laptop knows well: after years of intense usage, some components simply start to wear out.

The spacecraft arrived at Mars in December 2003, on what was planned to be a two-year mission. It has gone on to spend more than 14 years gathering a wealth of data from the Red Planet, taking high-resolution images of much of the surface, detecting minerals on the surface that form only in the presence of water, detecting hints of methane in the atmosphere and conducting close flybys of the enigmatic moon, Phobos.

Today, Mars Express is in good shape, with only some minor degradation in performance, but its gyroscopes are close to failing.

Gyros gone bad

These six gyros measure how much Mars Express rotates about any of its three axes. Together with the spacecraft's two startrackers, they determine its orientation in space.

This is critical for pointing its large parabolic radio antenna towards Earth and to aim its instruments – like the high-resolution stereo camera – at Mars.

Startrackers are simple, point-and-shoot cameras that capture images of the background star field and, with some clever processing, are used to determine the craft's orientation in space every few seconds.




Read more at: https://phys.org/news/2018-04-mars-v20.html#jCp
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Glad to see ESA going through what's needed to SAVE THE MISSION !!!

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Clear as mud: Desiccation cracks help reveal the shape of water on Mars
April 19, 2018, Geological Society of America


[Image: clearasmudde.jpg]
Curiosity Mastcam image of the Old Soaker rock slab taken on Sol 1555. The red-toned bed is covered by ridges that are the remnants of sediment that filled cracks that formed in drying lake in Gale Crater some ~3.5 billion years ago. The slab is about 80 cm across. Credit: NASA.
As Curiosity rover marches across Mars, the red planet's watery past comes into clearer focus.



In early 2017 scientists announced the discovery of possible desiccation cracks in Gale Crater, which was filled by lakes 3.5 billion years ago. Now, a new study has confirmed that these features are indeed desiccation cracks, and reveals fresh details about Mars' ancient climate.

"We are now confident that these are mudcracks," explains lead author Nathaniel Stein, a geologist at the California Institute of Technology in Pasadena. Since desiccation mudcracks form only where wet sediment is exposed to air, their position closer to the center of the ancient lake bed rather than the edge also suggests that lake levels rose and fell dramatically over time.

"The mudcracks show that the lakes in Gale Crater had gone through the same type of cycles that we see on Earth," says Stein. The study was published in Geology online ahead of print on 16 April 2018.

The researchers focused on a coffee table-sized slab of rock nicknamed "Old Soaker." Old Soaker is crisscrossed with polygons identical in appearance to desiccation features on Earth. The team took a close physical and chemical look at those polygons using Curiosity's Mastcam, Mars Hand Lens Imager, ChemCam Laser Induced Breakdown Spectrometer (LIBS), and Alpha-Particle X-Ray Spectrometer (APXS).

[Image: 1-clearasmudde.jpg]
Curiosity Mastcam image of the Squid Cove rock slab taken on Sol 1555. The red-toned bed is covered by ridges that are the remnants of sediment that filled cracks that formed in drying lake in Gale Crater some ~3.5 billion years ago. The cracks terminate at the underlying bed, which is coarser and did not fracture. The slab is about 60 cm across. Credit: NASA.

That close look proved that the polygons—confined to a single layer of rock and with sediment filling the cracks between them—formed from exposure to air, rather than other mechanisms such as thermal or hydraulic fracturing. And although scientists have known almost since the moment Curiosity landed in 2012 that Gale Crater once contained lakes, explains Stein, "the mudcracks are exciting because they add context to our understanding of this ancient lacustrine system."

"We are capturing a moment in time," he adds. "This research is just a chapter in a story that Curiosity has been building since the beginning of its mission."

[Image: 1x1.gif] Explore further: Mars rover Curiosity examines possible mud cracks

More information: N. Stein et al. Desiccation cracks provide evidence of lake drying on Mars, Sutton Island member, Murray formation, Gale Crater, Geology (2018). DOI: 10.1130/G40005.1


Read more at: https://phys.org/news/2018-04-mud-desicc...s.html#jCp
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