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  • richardmitnick 4:08 pm on September 25, 2014 Permalink | Reply
    Tags: , , , , , Water   

    From SPACE.com: “Much of Earth’s Water Is Older Than the Sun” 

    space-dot-com logo

    SPACE.com

    September 25, 2014
    Mike Wall

    Much of the water on Earth and elsewhere in the solar system likely predates the birth of the sun, a new study reports.

    space
    Planets form in the presence of abundant interstellar water inherited as ices from the parent molecular cloud.
    Credit: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)/ESO/J. Emerson/VISTA/Cambridge Astronomical Survey Unit

    The finding suggests that water is commonly incorporated into newly forming planets throughout the Milky Way galaxy and beyond, researchers said — good news for anyone hoping that Earth isn’t the only world to host life.

    “The implications of our study are that interstellar water-ice remarkably survived the incredibly violent process of stellar birth to then be incorporated into planetary bodies,” study lead author Ilse Cleeves, an astronomy Ph.D. student at the University of Michigan, told Space.com via email.

    “If our sun’s formation was typical, interstellar ices, including water, likely survive and are a common ingredient during the formation of all extrasolar systems,” Cleeves added. “This is particularly exciting given the number of confirmed extrasolar planetary systems to date — that they, too, had access to abundant, life-fostering water during their formation.”

    Astronomers have discovered nearly 2,000 exoplanets so far, and many billions likely lurk undetected in the depths of space. On average, every Milky Way star is thought to host at least one planet.

    water
    Artist’s concept showing the time sequence of water ice, starting in the sun’s parent molecular cloud, traveling through the stages of star formation, and eventually being incorporated into the planetary system itself.
    Credit: Bill Saxton, NSF/AUI/NRAO

    Water, water everywhere

    Our solar system abounds with water. Oceans of it slosh about not only on Earth’s surface but also beneath the icy shells of Jupiter’s moon Europa and the Saturn satellite Enceladus. And water ice is found on Earth’s moon, on comets, at the Martian poles and even inside shadowed craters on Mercury, the planet closest to the sun.

    Cleeves and her colleagues wanted to know where all this water came from.

    “Why is this important? If water in the early solar system was primarily inherited as ice from interstellar space, then it is likely that similar ices, along with the prebiotic organic matter that they contain, are abundant in most or all protoplanetary disks around forming stars,” study co-author Conel Alexander, of the Carnegie Institution for Science in Washington, D.C., said in a statement.

    “But if the early solar system’s water was largely the result of local chemical processing during the sun’s birth, then it is possible that the abundance of water varies considerably in forming planetary systems, which would obviously have implications for the potential for the emergence of life elsewhere,” Alexander added.

    Heavy and ‘normal’ water

    Not all water is “standard” H2O. Some water molecules contain deuterium, a heavy isotope of hydrogen that contains one proton and one neutron in its nucleus. (Isotopes are different versions of an element whose atoms have the same number of protons, but different numbers of neutrons. The most common hydrogen isotope, known as protium, for example, has one proton but no neutrons.)

    Because they have different masses, deuterium and protium behave differently during chemical reactions. Some environments are thus more conducive to the formation of “heavy” water — including super-cold places like interstellar space.

    The researchers constructed models that simulated reactions within a protoplanetary disk, in an effort to determine if processes during the early days of the solar system could have generated the concentrations of heavy water observed today in Earth’s oceans, cometary material and meteorite samples.

    The team reset deuterium levels to zero at the beginning of the simulations, then watched to see if enough deuterium-enriched ice could be produced within 1 million years — a standard lifetime for planet-forming disks.

    The answer was no. The results suggest that up to 30 to 50 percent of Earth’s ocean water and perhaps 60 to 100 percent of the water on comets originally formed in interstellar space, before the sun was born. (These are the high-end estimates generated by the simulations; the low-end estimates suggest that at least 7 percent of ocean water and at least 14 percent of comet water predates the sun.)

    While these findings, published online today (Sept. 25) in the journal Science, will doubtless be of interest to astrobiologists, they also resonated with Cleeves on a personal level, she said.

    “A significant fraction of Earth’s water is likely incredibly old, so old that it predates the Earth itself,” Cleeves said. “For me, uncovering these kinds of direct links between our daily experience and the galaxy at large is fascinating and puts a wonderful perspective on our place in the universe.”

    See the full article here.

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  • richardmitnick 8:45 am on August 21, 2014 Permalink | Reply
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    From Astrobiology: “Scientists Detect Evidence of ‘Oceans Worth’ of Water in Earth’s Mantle” 

    Astrobiology Magazine

    Astrobiology Magazine

    Aug 21, 2014
    Andrew Williams

    Researchers have found evidence of a potential “ocean’s worth” of water deep beneath the United States.

    Although not present in a familiar form, the building blocks of water are bound up in rock located deep in the Earth’s mantle, and in quantities large enough to represent the largest water reservoir on the planet, according to the research.

    For many years, scientists have attempted to establish exactly how much water may be cycling between the Earth’s surface and interior reservoirs through the action of plate tectonics. Northwestern University geophysicist Steve Jacobsen and University of New Mexico seismologist Brandon Schmandt have found deep pockets of magma around 400 miles beneath North America — a strong indicator of the presence of H₂O stored in the crystal structure of high-pressure minerals at these depths.

    “The total H₂O content of the planet has long been among the most poorly constrained ‘geochemical parameters’ in Earth science. Our study has found evidence for widespread hydration of the mantle transition zone,” says Jacobsen.

    For at least 20 years geologists have known from laboratory experiments that the Earth’s transition zone — a rocky layer of the Earth’s mantle located between the lower mantle and upper mantle, at depths between 250 and 410 miles — can, in theory, hold about 1 percent of its total weight as H₂O, bound up in minerals called wadsleyite and ringwoodite. However, as Schmandt explains, up until now it has been difficult to figure out whether that potential water reservoir is empty, as many have suggested, or not.

    If there does turn out to be a substantial amount of H₂O in the transition zone, then recent laboratory experiments conducted by Jacobsen indicate there should be large quantities of what he calls “partial melt” in areas where mantle flows downward out of the zone. This water-rich silicate melt is molten rock that occurs at grain boundaries between solid mineral crystals and may account for about 1 percent of the volume of rocks.

    two
    Brandon Schmandt (University of New Mexico, left) and Steve Jacobsen (Northwestern University, right) combined seismic observations from the US-Array with laboratory experiments to detect dehydration melting of hydrous mantle material beneath North America at depths of 700-800 km. Credit: University of New Mexico/Northwestern University

    “Melting occurs because hydrated rocks are carried from the transition zone, where the rocks can hold lots of H₂O, downward into the lower mantle, where the rocks cannot hold as much H₂O. Melting is the way to get rid of the H₂O that won’t fit in the crystal structure present in the lower mantle,” says Jacobsen.

    He adds:

    “When a rock starts to melt, whatever H₂O is bound in the rock will go into the melt right away. So the melt would have much higher H₂O concentration than the remaining solid. We’re not sure how it got there. Maybe it’s been stuck there since early in Earth’s history or maybe it’s constantly being recycled by plate tectonics.”

    Seismic Waves

    Melt strongly affects the speed of seismic waves — the acoustic-like waves of energy that travel through the Earth’s layers as a result of an earthquake or explosion. This is because stiff rocks, like the silicate-rich ones present in the mantle, propagate seismic waves very quickly. According to Schmandt, if just a little melt — even 1 percent or less — is added between the crystal grains of such a rock it causes it to become less stiff, meaning that elastic waves propagate more slowly.

    “We were able to analyse seismic waves from earthquakes to look for melt in the mantle just beneath the transition zone,” says Schmandt.

    “What we found beneath the U.S. is consistent with partial melt being present in areas of downward flow out of the transition zone. Without the presence of H₂O, it is very difficult to explain melting at these depths. This is a good hint that the transition zone H₂O reservoir is not empty, and even if it’s only partially filled that could correspond to about the same mass of H₂O as in Earth’s oceans,” he adds.

    Jacobsen and Schmandt hope that their findings, published in the June issue of the journal Science, will help other scientists to understand how the Earth formed and what its current composition and inner workings are, as well as establish how much water is trapped in mantle rock.

    “I think we are finally seeing evidence for a whole-Earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet. Scientists have been looking for this missing deep water for decades,” says Jacobsen

    Mantle Rock Studies

    The study combined Schmandt’s analysis of seismic data from the USArray, a network of over 2,000 seismometers across the U.S., with Jacobsen’s laboratory experiments, in which he examined the behaviour of mantle rock under conditions designed to simulate the high pressures and temperatures present at 400 miles below the Earth’s surface.

    globe
    Schematic representation of seismometers placed in the US-Array between 2004 and 2014 and used in the study by Schmandt and Jacobsen to detect dehydration melting at the top of the lower mantle beneath North America. Image Credit: NSF-Earthscope

    The USArray is part of Earthscope, a program sponsored by National Science Foundation. Jacobsen’s experiments were conducted at two Department of Energy. user facilities, the Advanced Photon Source of Argonne National Laboratory and the National Synchrotron Light Source at Brookhaven National Laboratory.

    Argonne APS
    APS at Argonne Lab

    Brookhaven NSLS
    NSLS at Brookhaven

    Taken as a whole, their findings produced strong evidence that melting may occur about 400 miles deep in the Earth, with H₂O stored in mantle rocks, such as those containing the mineral ringwoodite, which is likely to be a dominant mineral at those depths.

    Schmandt explains that he made this discovery after carrying out seismic imaging of the boundary between the transition zone and lower mantle. He found evidence that, in areas where “sharp transitions” like melt are present, some earthquake energy had converted from a compressional, or longitudinal wave, to a shear or S-wave. The phase of the converted S-waves in areas where the mantle is flowing down and out of the transition zone indicated a significantly lower velocity than surrounding mantle. The discovery suggests that water from the Earth’s surface can be driven to such great depths by plate tectonics, eventually resulting in the partial melting of the rocks found deep in the mantle.

    “We used many seismic wave conversions to see that many areas beneath the U.S. may have some melt just beneath the transition zone. The next step was comparing these areas to the areas where mantle flow models predict downward flow out of the transition zone,” says Schmandt.

    Ringwoodite

    Schmandt and Jacobsen’s findings build on a discovery reported in March in the journal Nature in which scientists discovered a piece of the blue mineral ringwoodite inside a diamond brought up from a depth of 400 miles by a volcano in Brazil. That tiny piece of ringwoodite — the only sample we have from within the Earth — contained a surprising amount of water bound in solid form in the mineral.

    “Not only was this the first terrestrial ringwoodite ever seen — all other natural ringwoodite examples came from shocked meteorites — but the tiny inclusion of ringwoodite was also full of H₂O, to about 1.5 percent of total weight,” says Jacobsen. “This is about the maximum amount of water that we are able to put into ringwoodite in laboratory experiments.”

    Although the discovery provided direct evidence of water in the deep mantle at about 700 kilometers (434 miles) deep, the diamond sampled only one point of the mantle. Jacobsen explains that the paper expands the search to question how widespread hydration might be throughout the entire transition zone. This is important because the presence of H₂O in the large volumes of rock found at depths of between 410 to 660 kilometers (255 to 410 miles) would “significantly alter our understanding of the composition of the Earth.”

    Crystals of laboratory-grown hydrous ringwoodite, a high-pressure polymorph of olivine that is stable from about 520-660 km depth in the Earth’s mantle. The ringwoodite pictured here contains around one weight percent of H2O, similar to what was inferred in the seismic observations made by Schmandt and Jacobsen. Image Credit: Steve Jacobsen/Northwestern University

    Crystals of laboratory-grown hydrous ringwoodite, a high-pressure polymorph of olivine that is stable from about 520-660 km depth in the Earth’s mantle. The ringwoodite pictured here contains around one weight percent of H2O, similar to what was inferred in the seismic observations made by Schmandt and Jacobsen. Image Credit: Steve Jacobsen/Northwestern University

    “It would double or triple the known amount of H₂O in the bulk Earth. Just 1 to 2 percent H₂O by weight in the transition zone would be equivalent to 2 to 3 times the amount of H₂O in the oceans,” adds Jacobsen.

    Big Questions

    Looking ahead, Jacobsen admits that some big questions remain. For example, if the transition zone is full of H₂O, what does this tell us about the origin of Earth’s water? And is the presence of ringwoodite in a planet’s mantle necessary for a planet to retain enough original water to form oceans? Moreover, how is the H₂O in the transition zone connected to the surface reservoirs? Is the transition zone, if it contains a geochemical reservoir of H₂O larger than the oceans, somehow buffering the amount of liquid water on the Earth’s surface?

    “An analogy could be that of a sponge, which needs to be filled before liquid water can be supported on top. Was water in the transition zone added through plate tectonics early in Earth’s history, or did the oceans de-gas from the mantle until an equilibrium was reached between surface and interior reservoirs?” asks Jacobsen.

    Either way, the research is likely to be of strong interest to astrobiologists largely because water is often so closely linked to the formation of biological life. Remote geochemical analysis could be one way of detecting if such processes occur elsewhere in the universe, and it is likely that such analysis would involve the use of gamma-ray, neutron, and x-ray spectrometers of the type used by the NASA MESSENGER spacecraft for the remote geochemical mapping of Mercury.

    NASA Messenger satellite
    NASA Messenger

    “On other hard to reach planets it’s not practical to apply the type of seismic imaging that I used. So my guess is that geochemical analysis of volcanic rocks from other planetary bodies may be our best way to test whether volatiles are stored in the planet’s interior,” says Schmandt.

    See the full article here.

    NASA

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  • richardmitnick 1:08 pm on June 18, 2014 Permalink | Reply
    Tags: , , Water   

    From SLAC Lab: “Scientists Take First Dip into Water’s Mysterious ‘No Man’s Land’” 


    SLAC Lab

    June 18, 2014
    Andy Freeberg, afreeberg@slac.stanford.edu, (650) 926-4359

    Scientists at the Department of Energy’s SLAC National Accelerator Laboratory have made the first structural observations of liquid water at temperatures down to minus 51 degrees Fahrenheit, within an elusive “no man’s land” where water’s strange properties are super-amplified.

    The research, made possible by SLAC’s Linac Coherent Light Source (LCLS) X-ray laser and reported June 18 in Nature, opens a new window for exploring liquid water in these exotic conditions, and promises to improve our understanding of its unique properties at the more natural temperatures and states that are relevant to global ocean currents, climate and biology.

    Scientists have known for some time that water can remain liquid at extremely cold temperatures, but they’ve never before been able to examine its molecular structure in this zone.

    “Water is not only essential for life as we know it, but it also has very strange properties compared to most other liquids,” said Anders Nilsson, deputy director of the SUNCAT Center for Interface Science and Catalysis, a joint SLAC/Stanford institute, and leader of the research. “Now, thanks to LCLS, we have finally been able to enter this cold zone that should provide new information about the unique nature of water.”

    Not Your Typical Liquid

    Despite its simple molecular structure, water has many weird traits: Its solid form is less dense than its liquid form, which is why ice floats; it can absorb a large amount of heat, which is carried long distances by ocean currents and has a profound impact on climate; and its peculiar density profile prevents oceans and lakes from freezing solid all the way to the bottom, allowing fish to survive the winter.

    These traits are amplified when purified water is supercooled. When water is very pure, with nothing to seed the formation of ice crystals, it can remain liquid at much lower temperatures than normal. The temperature range of water from about minus 42 to minus 172 degrees (see diagram) has been dubbed no man’s land. For decades scientists have sought to better explore what happens to water molecules at temperatures below minus 42 degrees, but they had to rely largely on theory and modeling.

    graph
    This diagram illustrates the rough boundaries of “no man’s land,” a temperature region where supercooled water is difficult to study because of rapid ice formation. Using SLAC’s Linac Coherent Light Source, scientists dipped down to minus 51 degrees Fahrenheit and made the first structural measurements of liquid water in this mysterious region, where water’s unusual properties are amplified. (Greg Stewart/SLAC, Ultrafast Chemical Physics Group/University of Glasgow, Scotland)

    Femtosecond Shutter Speeds

    Now the LCLS, with X-ray laser pulses just quadrillionths of a second long, allows researchers to capture rapid-fire snapshots showing the detailed molecular structure of water in this mysterious zone the instant before it freezes. The research showed that water’s molecular structure transforms continuously as it enters this realm, and with further cooling the structural changes accelerate more dramatically than theoretical models had predicted.

    For this experiment, researchers produced a steady flow of tiny water droplets in a vacuum chamber. As the drops traveled toward the laser beam, some of their liquid rapidly evaporated, supercooling the remaining liquid. (The same process cools us when we sweat.) By adjusting the distance the droplets traveled, the researchers were able to fine-tune the temperatures they reached on arrival at the X-ray laser beam.

    Colder Still

    Nilsson’s team hopes to dive to even colder temperatures where water morphs into a glassy, non-crystalline solid. They also want to determine whether supercooled water reaches a critical point where its unusual properties peak, and to pinpoint the temperature at which this occurs.

    “Our dream is to follow these dynamics as far as we can,” Nilsson said. “Eventually our understanding of what’s happening here in no man’s land will help us fundamentally understand water in all conditions.”

    Scientists at SLAC’s Linac Coherent Light Source, Stanford Synchrotron Radiation Lightsource and Stanford PULSE Institute; Stockholm University; Germany’s DESY laboratory; the Helmholtz Center for Materials and Energy in Germany; and Stony Brook University in New York also contributed to the research. The work was partially funded by the U.S. Department of Energy Office of Science, the SLAC Laboratory Directed Research and Development Program and the Swedish Research Council.

    See the full article here.

    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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  • richardmitnick 12:48 pm on June 18, 2014 Permalink | Reply
    Tags: , , , , Water   

    From Princeton: “Familiar yet strange: Water’s ‘split personality’ revealed by computer model” 

    Princeton University
    Princeton University

    June 18, 2014
    Catherine Zandonella, Office of the Dean for Research

    Seemingly ordinary, water has quite puzzling behavior. Why, for example, does ice float when most liquids crystallize into dense solids that sink?

    Using a computer model to explore water as it freezes, a team at Princeton University has found that water’s weird behaviors may arise from a sort of split personality: at very cold temperatures and above a certain pressure, water may spontaneously split into two liquid forms.

    The team’s findings were reported in the journal Nature.

    “Our results suggest that at low enough temperatures water can coexist as two different liquid phases of different densities,” said Pablo Debenedetti, the Class of 1950 Professor in Engineering and Applied Science and Princeton’s dean for research, and a professor of chemical and biological engineering.

    The two forms coexist a bit like oil and vinegar in salad dressing, except that the water separates from itself rather than from a different liquid. “Some of the molecules want to go into one phase and some of them want to go into the other phase,” said Jeremy Palmer, a postdoctoral researcher in the Debenedetti lab.

    The finding that water has this dual nature, if it can be replicated in experiments, could lead to better understanding of how water behaves at the cold temperatures found in high-altitude clouds where liquid water can exist below the freezing point in a “supercooled” state before forming hail or snow, Debenedetti said. Understanding how water behaves in clouds could improve the predictive ability of current weather and climate models, he said.

    chart
    Pressure–temperature phase diagram, including an illustration of the liquid–liquid transition line proposed for several polyamorphous materials. This liquid–liquid phase transition would be a first order, discontinuous transition between low and high density liquids (labelled 1 and 2). This is analogous to polymorphism of crystalline materials, where different stable crystalline states (solid 1, 2 in diagram) of the same substance can exist (e.g. diamond and graphite are two polymorphs of carbon). Like the ordinary liquid–gas transition, the liquid–liquid transition is expected to end in a critical point. At temperatures beyond these critical points there is a continuous range of fluid states, i.e. the distinction between liquids and gasses is lost. If crystallisation is avoided the liquid–liquid transition can be extended into the metastable supercooled liquid regime.

    The new finding serves as evidence for the “liquid-liquid transition” hypothesis, first suggested in 1992 by Eugene Stanley and co-workers at Boston University and the subject of recent debate. The hypothesis states that the existence of two forms of water could explain many of water’s odd properties — not just floating ice but also water’s high capacity to absorb heat and the fact that water becomes more compressible as it gets colder.

    deb
    Princeton University researchers conducted computer simulations to explore what happens to water as it is cooled to temperatures below freezing and found that the supercooled liquid separated into two liquids with different densities. The finding agrees with a two-decade-old hypothesis to explain water’s peculiar behaviors, such as becoming more compressible and less dense as it is cooled. The X axis above indicates the range of crystallinity (Q6) from liquid water (less than 0.1) to ice (greater than 0.5) plotted against density (ρ) on the Y axis. The figure is a two-dimensional projection of water’s calculated “free energy surface,” a measure of the relative stability of different phases, with orange indicating high free energy and blue indicating low free energy. The two large circles in the orange region reveal a high-density liquid at 1.15 g/cm3 and low-density liquid at 0.90 g/cm3. The blue area represents cubic ice, which in this model forms at a density of about 0.88 g/cm3. (Image courtesy of Jeremy Palmer)

    At cold temperatures, the molecules in most liquids slow to a sedate pace, eventually settling into a dense and orderly solid that sinks if placed in liquid. Ice, however, floats in water due to the unusual behavior of its molecules, which as they get colder begin to push away from each other. The result is regions of lower density — that is, regions with fewer molecules crammed into a given volume — amid other regions of higher density. As the temperature falls further, the low-density regions win out, becoming so prevalent that they take over the mixture and freeze into a solid that is less dense than the original liquid.

    The work by the Princeton team suggests that these low-density and high-density regions are remnants of the two liquid phases that can coexist in a fragile, or “metastable” state, at very low temperatures and high pressures. “The existence of these two forms could provide a unifying theory for how water behaves at temperatures ranging from those we experience in everyday life all the way to the supercooled regime,” Palmer said.

    Since the proposal of the liquid-liquid transition hypothesis, researchers have argued over whether it really describes how water behaves. Experiments would settle the debate, but capturing the short-lived, two-liquid state at such cold temperatures and under pressure has proved challenging to accomplish in the lab.

    Instead, the Princeton researchers used supercomputers to simulate the behavior of water molecules — the two hydrogens and the oxygen that make up “H2O” — as the temperature dipped below the freezing point.

    The team used computer code to represent several hundred water molecules confined to a box, surrounded by an infinite number of similar boxes. As they lowered the temperature in this virtual world, the computer tracked how the molecules behaved.

    The team found that under certain conditions — about minus 45 degrees Celsius and about 2,400-times normal atmospheric pressure — the virtual water molecules separated into two liquids that differed in density.

    The pattern of molecules in each liquid also was different, Palmer said. Although most other liquids are a jumbled mix of molecules, water has a fair amount of order to it. The molecules link to their neighbors via hydrogen bonds, which form between the oxygen of one molecule and a hydrogen of another. These molecules can link — and later unlink — in a constantly changing network. On average, each H2O links to four other molecules in what is known as a tetrahedral arrangement.

    The researchers found that the molecules in the low-density liquid also contained tetrahedral order, but that the high-density liquid was different. “In the high-density liquid, a fifth neighbor molecule was trying to squeeze into the pattern,” Palmer said.

    image
    Normal ice (left) contains water molecules linked into ring-like structures via hydrogen bonds (dashed blue lines) between the oxygen atoms (red beads) and hydrogen atoms (white beads) of neighboring molecules, with six water molecules per ring. Each water molecule in ice also has four neighbors that form a tetrahedron (right), with a center molecule linked via hydrogen bonds to four neighboring molecules. The green lines indicate the edges of the tetrahedron. Water molecules in liquid water form distorted tetrahedrons and ring structures that can contain more or less than six molecules per ring. (Image courtesy of Jeremy Palmer)

    The researchers also looked at another facet of the two liquids: the tendency of the water molecules to form rings via hydrogen bonds. Ice consists of six water molecules per ring. Calculations by Fausto Martelli, a postdoctoral research associate advised by Roberto Car, the Ralph W. *31 Dornte Professor in Chemistry, found that in this computer model the average number of molecules per ring decreased from about seven in the high-density liquid to just above six in the low-density liquid, but then climbed slightly before declining again to six molecules per ring as ice, suggesting that there is more to be discovered about how water molecules behave during supercooling.

    A better understanding of water’s behavior at supercooled temperatures could lead to improvements in modeling the effect of high-altitude clouds on climate, Debenedetti said. Because water droplets reflect and scatter the sunlight coming into the atmosphere, clouds play a role in whether the sun’s energy is reflected away from the planet or is able to enter the atmosphere and contribute to warming. Additionally, because water goes through a supercooled phase before forming hail or snow, such research may aid strategies for preventing ice from forming on airplane wings.

    “The research is a tour de force of computational physics and provides a splendid academic look at a very difficult problem and a scholarly controversy,” said C. Austen Angell, professor of chemistry and biochemistry at Arizona State University, who was not involved in the research. “Using a particular computer model, the Debenedetti group has provided strong support for one of the theories that can explain the outstanding properties of real water in the supercooled region.”

    In their computer simulations, the team used an updated version of a model noted for its ability to capture many of water’s unusual behaviors first developed in 1974 by Frank Stillinger, then at Bell Laboratories in Murray Hill, N.J., and now a senior chemist at Princeton; and Aneesur Rahman, then at the U.S. Argonne National Laboratory. The same model was used to develop the liquid-liquid transition hypothesis.

    Collectively, the work took several million computer hours, which would take several human lifetimes using a typical desktop computer, Palmer said. In addition to the initial simulations, the team verified the results using six calculation methods. The computations were performed at Princeton’s High-Performance Computing Research Center’s Terascale Infrastructure for Groundbreaking Research in Science and Engineering (TIGRESS).

    The team included Yang Liu, who earned her doctorate at Princeton in 2012, and Athanassios Panagiotopoulos, the Susan Dod Brown Professor of Chemical and Biological Engineering.

    Support for the research was provided by the National Science Foundation (CHE 1213343) and the U.S. Department of Energy (DE-SC0002128 and DE-SC0008626).

    The article, Metastable liquid-liquid transition in a molecular model of water, by Jeremy C. Palmer, Fausto Martelli, Yang Liu, Roberto Car, Athanassios Z. Panagiotopoulos and Pablo G. Debenedetti, appeared in the journal Nature.

    See the full article here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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