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  • richardmitnick 12:32 pm on March 1, 2019 Permalink | Reply
    Tags: "Department of Energy moves forward with controversial test reactor", a.k.a. the Versatile Fast Neutron Source, “It will give American companies the ability that they currently lack to conduct advanced technology and fuels tests without having to go to our competitors in Russia or China.”, Could also convert nonfissile uranium-238 to plutonium-239 which could be extracted by reprocessing the fuel, Many nuclear engineers envision a future in which the world relies on such fast reactors and reprocessed fuel for its electricity, Science Magazine, The VTR already has friends in both parties in Congress, The VTR would use a fuel richer in uranium-235 that would generate more high-energy neutrons as it “burned.”, VTR-Versatile Test Reactor   

    From Science Magazine: “Department of Energy moves forward with controversial test reactor” 

    AAAS
    From Science Magazine

    Feb. 28, 2019
    Adrian Cho

    1
    A new “fast” nuclear reactor would work a bit like the Experimental Breeder Reactor-II, which ran until 1994 at what is now Idaho National Laboratory.
    IDAHO NATIONAL LABORATORY

    The U.S. Department of Energy (DOE) announced today that it will go forward with plans to build a controversial new nuclear reactor that some critics have called a boondoggle. If all goes as planned, the Versatile Test Reactor (VTR) will be built at DOE’s Idaho National Laboratory (INL) near Idaho Falls and will generate copious high-energy neutrons to test new material and technologies for nuclear reactors. That would fill a key gap in the United States’s nuclear capabilities, proponents say. However, some critics have argued that the project is just an excuse to build a reactor of the general type that can generate more fuel than it consumes by “breeding” plutonium.

    “This is a cutting-edge advanced reactor,” said Secretary of Energy Rick Perry at a press conference today at DOE headquarters in Washington, D.C. “It will give American companies the ability that they currently lack to conduct advanced technology and fuels tests without having to go to our competitors in Russia or China.”

    Kemal Pasamehmetoglu, a nuclear engineer at INL who leads the project and was not at the press conference, says, “Obviously, this is very good news. It validates that we need this reactor.”

    The VTR—also known as the Versatile Fast Neutron Source—would be the first reactor DOE has built since the 1970s. It would differ in one key respect from the typical commercial power reactors. Power reactors use a uranium fuel that contains just a few percents of the fissile isotope uranium-235 and are made to be used once and discarded. In contrast, the VTR would use a fuel richer in uranium-235 that would generate more high-energy neutrons as it “burned.” Those neutrons could be used to test how new materials and components age within the core of a conventional nuclear reactor, a key factor in reactor design.

    In principle, such a “fast reactor” could also convert nonfissile uranium-238 to plutonium-239, which could be extracted by reprocessing the fuel. Many nuclear engineers envision a future in which the world relies on such fast reactors and reprocessed fuel for its electricity. Some critics of the nuclear industry claim the VTR is a way to keep that dream alive—although VTR developers do not plan to breed and reprocess fuel.

    The VTR already has friends in both parties in Congress, which in September 2018 gave the project $65 million for this fiscal year—even before DOE had definitely decided it wanted the reactor. However, Pasamehmetoglu urges caution about interpreting the DOE announcement. Strictly speaking, he says, it means the project has passed the first of five milestones—known as “critical decisions”—and that DOE has decided it needs the VTR to fulfill its mission. “It’s just a start,” Pasamehmetoglu says. “It doesn’t mean by any stretch of the imagination that DOE has said that they’re going to go out and build this.”

    Still, Pasamehmetoglu is optimistic. Researchers will now start to work on a conceptual design. They are still a couple of steps away from hammering out a detailed cost estimate and schedule. But Pasamehmetoglu estimates the reactor would cost between $3 billion and $3.5 billion and says the goal is to get it running in 2026. It would be a small 300-megawatt reactor, most likely cooled with liquid sodium, that would not produce electrical power.

    At the press conference, held with Fatih Birol, executive director of the International Energy Agency in Paris, Perry also announced $24 million in new projects on technologies to capture carbon dioxide emissions from industrial plants and sequester the gas underground. “We believe that you can’t have a serious conversation about reducing emissions without including nuclear energy and carbon capture technologies,” Perry said. He noted projections suggest that in 2040 the world will still depend on fossil fuels for 77% of its energy, and in just the next 18 months U.S. exports of liquid natural gas should climb 150%, Perry said.

    See the full article here .


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  • richardmitnick 3:23 pm on February 27, 2019 Permalink | Reply
    Tags: A one-stop link allowing earth scientists to access all the data they need to tackle big questions such as patterns of biodiversity over geologic time and the distribution of metal deposits also the w, , British Geological Survey, , , Science Magazine, This network of earth science databases called Deep-time Digital Earth (DDE)   

    From Science Magazine: “Earth scientists plan to meld massive databases into a ‘geological Google’’ 

    AAAS
    From Science Magazine

    Feb. 26, 2019
    Dennis Normile

    1
    Deep-time Digital Earth aims to liberate data from collections such as the British Geological Survey’s. British Geological Survey.

    The British Geological Survey (BGS) has amassed one of the world’s premier collections of geologic samples. Housed in three enormous warehouses in Nottingham, U.K., it contains about 3 million fossils gathered over more than 150 years at thousands of sites across the country. But this data trove “was not really very useful to anybody,” says Michael Stephenson, a BGS paleontologist. Notes about the samples and their associated rocks “were sitting in boxes on bits of paper.” Now, that could change, thanks to a nascent international effort to meld earth science databases into what Stephenson and other backers are describing as a “geological Google.”

    This network of earth science databases, called Deep-time Digital Earth (DDE), would be a one-stop link allowing earth scientists to access all the data they need to tackle big questions, such as patterns of biodiversity over geologic time, the distribution of metal deposits, and the workings of Africa’s complex groundwater networks. It’s not the first such effort, but it has a key advantage, says Isabel Montañez, a geochemist at University of California, Davis, who is not involved in the project: funding and infrastructure support from the Chinese government. That backing “will be critical to [DDE’s] success given the scope of the proposed work,” she says.

    In December 2018, DDE won the backing of the executive committee of the International Union of Geological Sciences, which said ready access to the collected geodata could offer “insights into the distribution and value of earth’s resources and materials, as well as hazards—while also providing a glimpse of the Earth’s geological future.” At a meeting this week in Beijing, 80 scientists from 40 geoscience organizations including BGS and the Russian Geological Research Institute are discussing how to get DDE up and running by the time of the International Geological Congress in New Delhi in March 2020.

    DDE grew out of a Chinese data digitization scheme called the Geobiodiversity Database (GBDB), initiated in 2006 by Chinese paleontologist Fan Junxuan of Nanjing University. China had long-running efforts in earth sciences, but the data were scattered among numerous collections and institutions. Fan, who was then at the Chinese Academy of Sciences’s Nanjing Institute of Geology and Paleontology, organized GBDB around the stacks of geologic strata called sections and the rocks and fossils in each stratum.

    Norman MacLeod, a paleobiologist at the Natural History Museum in London who is advising DDE, says GBDB has succeeded where similar efforts have stumbled. In the past, he says, volunteer earth scientists tried to do nearly everything themselves, including informatics and data management. GBDB instead pays nonspecialists to input reams of data gleaned from earth science journals covering Chinese findings. Then, paleontologists and stratigraphers review the data for accuracy and consistency, and information technology specialists curate the database and create software to search and analyze the data. Consistent funding also contributed to GBDB’s success, MacLeod says. Although it started small, Fan says GBDB now runs on “several million” yuan per year.

    Earth scientists outside China began to use GBDB, and it became the official database of the International Commission on Stratigraphy in 2012. BGS decided to partner with GBDB to lift its data “from the page and into cyberspace,” as Stephenson puts it. He and other European and Chinese scientists then began to wonder whether the informatics tools developed for GBDB could help create a broader union of databases. “Our idea is to take these big databases and make them use the same standards and references so a researcher could quickly link them to do big science that hasn’t been done before,” he says.

    The Beijing meeting aims to finalize an organizational structure for DDE. Chinese funding agencies are putting up $75 million over 10 years to get the effort off the ground, Fan says. That level of support sets DDE apart from other cyberinfrastructure efforts “that are smaller in scope and less well funded,” Montañez says. Fan hopes DDE will also attract international support. He envisions nationally supported DDE Centers of Excellence that would develop databases and analytical tools for particular interests. Suzhou, China, has already agreed to host the first of them, which will also house the DDE secretariat.

    DDE backers say they want to cooperate with other geodatabase programs, such as BGS’s OneGeology project, which seeks to make geologic maps of the world available online. But Mohan Ramamurthy, project director of the U.S. National Science Foundation–funded EarthCube project, sees little scope for collaboration with his effort, which focuses on current issues such as climate change and biosphere-geosphere interactions. “The two programs have very different objectives with little overlap,” he says.

    Fan also hopes individual institutions will contribute, by sharing data, developing analytical tools, and encouraging their scientists to participate. Once earth scientists are freed of the drudgery of combing scattered collections, he says, they will have time for more important challenges, such as answering “questions about the evolution of life, materials, geography, and climate in deep time.”

    See the full article here .


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  • richardmitnick 12:33 pm on February 23, 2019 Permalink | Reply
    Tags: Astronomers discover solar system’s most distant object [so far] nicknamed ‘FarFarOut’ ", , , , , Science Magazine   

    From Science Magazine: “Astronomers discover solar system’s most distant object [so far] , nicknamed ‘FarFarOut’ “ 

    AAAS
    From Science Magazine

    Feb. 21, 2019
    Paul Voosen

    1
    The solar system’s most distant object is 140 times farther from the sun than Earth. Credit: NASA/JPL-Caltech

    For most people, snow days aren’t very productive. Some people, though, use the time to discover the most distant object in the solar system.

    That’s what Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington, D.C., did this week when a snow squall shut down the city. A glitzy public talk he was due to deliver was delayed, so he hunkered down and did what he does best: sifted through telescopic views of the solar system’s fringes that his team had taken last month during their search for a hypothesized ninth giant planet.

    That’s when he saw it, a faint object at a distance 140 times farther from the sun than Earth—the farthest solar system object yet known, some 3.5 times more distant than Pluto. The object, if confirmed, would break his team’s own discovery, announced in December 2018, of a dwarf planet 120 times farther out than Earth, which they nicknamed “Farout.” For now, they are jokingly calling the new object “FarFarOut.” “This is hot off the presses,” he said during his rescheduled talk on 21 February.

    For the better part of a decade, Sheppard and his collaborators—Chad Trujillo at Northern Arizona University in Flagstaff and Dave Tholen at the University of Hawaii in Honolulu—have methodically scoured the night sky with some of the world’s most powerful and wide-angled telescopes. Their insistent search has netted four-fifths of the objects known past 9 billion kilometers from the sun.

    This is not stamp collecting. Clustering in the orbits of these objects can serve as indicators of Planet Nine’s influence. Like Farout, FarFarOut’s orbit is not yet known; until it is, it’s uncertain whether it will stay far enough away from the rest of the solar system to be free of the giant planets’ gravitational tug. If it does, the two could join another of Sheppard’s recent distant discoveries, “the Goblin,” which dovetails with projections of the Planet Nine’s possible orbit.

    It will take several years to determine the orbits of Farout and FarFarOut, and whether they will provide more clues. Meanwhile, with nearly every new moon, Sheppard is back out searching on his preferred telescopes, the Blanco 4-meter in Chile and the Subaru 8-meter in Hawaii. He flies to Chile next week, and Hawaii the week after.


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet


    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level

    See the full article here .


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  • richardmitnick 10:59 am on February 22, 2019 Permalink | Reply
    Tags: , LLC, Nuclear power scheme-Twelve-pack of power. C. BICKEL/SCIENCE, NUSCALE POWER, , Science Magazine   

    From Science Magazine: “Smaller, safer, cheaper: One company aims to reinvent the nuclear reactor and save a warming planet” 

    AAAS
    From Science Magazine

    Feb. 21, 2019
    Adrian Cho

    1
    NuScale researchers want to operate 12 small nuclear reactors from a single control room. They built a mock one in Corvallis, Oregon, to show they can do it.
    NUSCALE POWER, LLC

    To a world facing the existential threat of global warming, nuclear power would appear to be a lifeline. Advocates say nuclear reactors, compact and able to deliver steady, carbon-free power, are ideal replacements for fossil fuels and a way to slash greenhouse gas emissions. However, in most of the world, the nuclear industry is in retreat. The public continues to distrust it, especially after three reactors melted down in a 2011 accident at the Fukushima Daiichi Nuclear Power Plant in Japan. Nations also continue to dither over what to do with radioactive reactor waste. Most important, with new reactors costing $7 billion or more, the nuclear industry struggles to compete with cheaper forms of energy, such as natural gas. So even as global temperatures break one record after another, just one nuclear reactor has turned on in the United States in the past 20 years. Globally, nuclear power supplies just 11% of electrical power, down from a high of 17.6% in 1996.

    Jose Reyes, a nuclear engineer and cofounder of NuScale Power, headquartered in Portland, Oregon, says he and his colleagues can revive nuclear by thinking small. Reyes and NuScale’s 350 employees have designed a small modular reactor (SMR) that would take up 1% of the space of a conventional reactor. Whereas a typical commercial reactor cranks out a gigawatt of power, each NuScale SMR would generate just 60 megawatts. For about $3 billion, NuScale would stack up to 12 SMRs side by side, like beer cans in a six-pack, to form a power plant.

    But size alone isn’t a panacea. “If I just scale down a large reactor, I’ll lose, no doubt,” says Reyes, 63, a soft-spoken native of New York City and son of Honduran and Dominican immigrants. To make their reactors safer, NuScale engineers have simplified them, eliminating pumps, valves, and other moving parts while adding safeguards in a design they say would be virtually impervious to meltdown. To make their reactors cheaper, the engineers plan to fabricate them whole in a factory instead of assembling them at a construction site, cutting costs enough to compete with other forms of energy.

    Spun out of nearby Oregon State University (OSU) here in 2007, NuScale has spent more than $800 million on its design—$288 million from the Department of Energy (DOE) and the rest mainly from NuScale’s backer, the global engineering and construction firm Fluor.

    The design is now working its way through licensing with the Nuclear Regulatory Commission (NRC), and the company has lined up a first customer, a utility association that wants to start construction on a plant in Idaho in 2023.

    NuScale is far from alone. With similar projects rising in China and Russia, the company is riding a global wave of interest in SMRs. “SMRs as a class have a potential to change the economics,” says Robert Rosner, a physicist at the University of Chicago in Illinois who co-wrote a 2011 report on them. In the United States, NuScale is the only company seeking to license and build an SMR. Rosner is optimistic about its prospects. “NuScale has really made the case that they’ll be able to pull it off,” Rosner says.

    For now, NuScale’s reactors exist mostly as computer models. But in an industrial area north of town here, the company has built a full-size mock-up of the upper portion of a reactor. Festooned with pipes, the 8-meter-tall gray cylinder isn’t exactly small. It resembles the conning tower of a submarine, one that has somehow surfaced through the dusty ground. NuScale built it to see if workers could squeeze inside for inspections, says Ben Heald, a NuScale reactor designer. “It’s a great marketing tool.”

    Not everyone thinks NuScale will make the transition from mock-up to reality, however. Dozens of advanced reactor designs have come and gone. And even if NuScale and other startups succeed, the nuclear industry won’t build enough plants quickly enough to matter in the fight against climate change, says Allison Macfarlane, a professor of public policy and geologist at George Washington University in Washington, D.C., who chaired NRC from 2012 through 2014. “Nuclear does not do anything quickly,” she says.

    Nuclear power scheme-Twelve-pack of power. C. BICKEL/SCIENCE

    A nuclear reactor is a glorified boiler. Within its core hang ranks of fuel rods, usually filled with pellets of uranium oxide. The radioactive uranium atoms spontaneously split, releasing energy and neutrons that go on to split more uranium atoms in a chain reaction called fission. Heat from the chain reaction ultimately boils water to drive steam turbines and generate electricity.

    Designs vary, but 85% of the world’s 452 power reactors circulate water through the core to cool it and ferry heat to a steam generator that drives a turbine.

    The water plays a second safety role. Power reactors typically use a fuel with a small amount of the fissile isotope uranium-235. The dilute fuel sustains a chain reaction only if the neutrons are slowed to increase the probability that they’ll split other atoms. The cooling water itself serves to slow, or moderate, the neutrons. If that water is lost in an accident, fission fizzles, preventing a runaway chain reaction like the one that blew up a graphite-moderated reactor in 1986 at the Chernobyl Nuclear Power Plant in Ukraine.

    Even after the chain reaction dies, however, heat from the radioactive decay of nuclei created by fission can melt the core. That happened at Fukushima when a tsunami swamped the emergency generators needed to pump water through the plant’s reactors.

    NuScale’s design would reduce such risks in multiple ways. First, in an accident the small cores would produce far less decay heat. NuScale engineers have also cut out the pumps that drive the cooling water through the core, relying instead on natural convection. That design eliminates moving parts that could fail and cause an accident in the first place, says Eric Young, a NuScale engineer. “If it’s not there, it can’t break,” he says.

    NuScale’s new reactor housings offer further protection. A conventional reactor sits within a reinforced concrete containment vessel up to 40 meters in diameter. Each 3-meter-wide NuScale reactor nestles into its own 4.6-meter-wide steel containment vessel, which by virtue of its much smaller diameter can withstand pressures 15 times greater. The vessels sit submerged in a vast pool of water: NuScale’s ultimate line of defense.

    For example, in an emergency, operators can cool the core by diverting steam from the turbines to heat exchangers in the pool. During normal operations, the space between the reactor and the containment vessel is kept under vacuum, like a thermos, to insulate the core and allow it to heat up. But if the reactor overheats, relief valves would pop open to release steam and water into the vacuum space, where they would transfer heat to the pool. Such passive features ensure that in just about any conceivable accident, the core would remain intact, Reyes says.

    To prove that the reactor will behave as predicted, NuScale engineers have constructed a one-third scale model. A 7-meter tall tangle of pipes, valves, and wires lurks in the corner of a lab at OSU’s department of nuclear engineering. The model aims not to run exactly like the real reactor, Young says, but rather to validate the computer models that NRC will use to evaluate the design’s safety. The model’s core heats water not with nuclear fuel but with 56 electric heaters like those in curling irons, Young says. “It’s like a big percolator,” he says. “We set up a test and watch coffee being made for 3 days.”

    Making a reactor smaller has a downside, says M. V. Ramana, a physicist at the University of British Columbia in Vancouver, Canada. A smaller reactor will extract less energy from every ton of fuel, he argues, driving up operating costs. “There’s a reason reactors became larger,” Ramana says. “Inherently, NuScale is giving up the advantages of economies of scale.”

    But small size pays off in versatility, Reyes says. One little reactor might power a plant to desalinate seawater or supply heat for an industrial process. A customized NuScale plant might support a developing country’s smaller electrical grid. And in the developed world, where intermittent renewable sources are growing rapidly, a full 12-pack of reactors could provide steady power to make up for the fitful output of windmills and solar panels. By varying the number of reactors producing power, a NuScale plant could “load follow” and fill in the gaps, Reyes says.

    See the full article here .


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  • richardmitnick 10:34 am on February 22, 2019 Permalink | Reply
    Tags: "Did volcanic eruptions help kill off the dinosaurs?", A large impact crater in the Gulf of Mexico, A massive asteroid strike 66 million years ago that unleashed towering tsunamis and blotted out the sun with ash causing a plunge in global temperatures, Across what is India today countless volcanic seams opened in the ground releasing a flood of lava resembling last year’s eruptions in Hawaii—except across an area the size of Texas, , Over the course of 1 million years the greenhouse gases from these eruptions could have raised global temperatures and poisoned the oceans leaving life in a perilous state before the asteroid impact, Science Magazine, Some 400000 years before the impact the planet gradually warmed by some 5°C only to plunge in temperature right before the mass extinction, The Deccan Traps,   

    From Science Magazine: “Did volcanic eruptions help kill off the dinosaurs?” 

    AAAS
    From Science Magazine

    Feb. 21, 2019
    Paul Voosen

    1
    The hardened lava flows of the Deccan Traps, in western India, may have played a role in the demise of the dinosaurs. Gerta Keller

    What killed off the dinosaurs? The answer has seemed relatively simple since the discovery a few decades ago of a large impact crater in the Gulf of Mexico. It pointed to a massive asteroid strike 66 million years ago that unleashed towering tsunamis and blotted out the sun with ash, causing a plunge in global temperatures.

    But the asteroid wasn’t the only catastrophe to wallop the planet around this time. Across what is India today, countless volcanic seams opened in the ground, releasing a flood of lava resembling last year’s eruptions in Hawaii—except across an area the size of Texas. Over the course of 1 million years, the greenhouse gases from these eruptions could have raised global temperatures and poisoned the oceans, leaving life in a perilous state before the asteroid impact.

    The timing of these eruptions, called the Deccan Traps, has remained uncertain, however. And scientists such as Princeton University’s Gerta Keller have acrimoniously debated [Science] how much of a role they played in wiping out 60% of all the animal and plant species on Earth, including most of the dinosaurs.

    That debate won’t end today. But two studies published in Science have provided the most precise dates for the eruptions so far—and the best evidence yet that the Deccan Traps may have played some role in the dinosaurs’ demise.

    There’s long been evidence that Earth’s climate was changing before the asteroid hit. Some 400,000 years before the impact, the planet gradually warmed by some 5°C, only to plunge in temperature right before the mass extinction. Some thought the Deccan Traps could be responsible for this warming, suggesting 80% of the lava had erupted before the impact.

    But the new studies counter that old view. In one, Courtney Sprain, a geochronologist at the University of Liverpool in the United Kingdom, and colleagues took three trips to India’s Western Ghats, home of some of the thickest lava deposits from the Deccan Traps. They sampled various basaltic rocks formed by the cooled lava. The technique they used, called argon-argon dating, dates the basalt’s formation, giving a direct sense of the eruptions’ timing.

    The researchers’ dates suggest the eruptions began 400,000 years before the impact, and kicked into high gear afterward, releasing 75% of their total volume [Science]in the 600,000 years after the asteroid strike. If the Deccan Traps had kicked off global warming, their carbon dioxide (CO2) emissions had to come before the lava flows really got going—which, Sprain adds, is plausible, given how much CO2 scientists see leaking from modern volcanoes, even when they’re not erupting.

    The dates, and the increase in lava volume after the impact, also line up with a previous suggestion by Sprain’s team, including her former adviser, Paul Renne, a geochronologist at the University of California, Berkeley, that the two events are directly related: The impact might have struck the planet so hard that it sent the Deccan Traps into eruptive high gear [Science].

    The second study used a different method to date the eruptions. A team including Keller and led by Blair Schoene, a geochronologist at Princeton, looked at zircon crystals [Science] trapped between layers of basalt. These zircons can be precisely dated using the decay of uranium to lead, providing time stamps for the layers bracketing the eruptions. The zircons are also rare: It was a full-time job, lasting several years, to sift them out from the rocks at the 140 sites they sampled.

    The dates recovered from the crystals suggest that the Deccan Traps erupted in four intense pulses [Science] rather than continuously, as Sprain suggests. One pulse occurred right before the asteroid strike. That suggests the impact did not trigger the eruptions, he says. Instead, it’s possible this big volcanic pulse before the asteroid impact did play a role in the extinction, Schoene says. “It’s very tempting to say.” But, he adds, there’s never been a clear idea of how exactly these eruptions could directly cause such extinctions.

    Though the two studies differ, they largely agree on the overall timing of the Deccan eruptions, Schoene says. “If you plot the data sets over each other, there’s almost perfect agreement.”

    This match represents a victory, says Noah McLean, a geochemist at the University of Kansas in Lawrence, who was not involved in either study. For decades, dates produced with these geochronological techniques couldn’t line up. But improved techniques and calibration, McLean says, “helped us go from million-year uncertainties to tight chronologies.”

    Solving the mystery of how the dinosaurs died isn’t just an academic problem. Understanding how the eruptions’ injection of CO2 into the atmosphere changed the planet is vital not only for our curiosity about the dinosaurs’ end, but also as an analog for today, Sprain says. “This is the most recent mass extinction we have,” Sprain says. Teasing apart the roles of the impact and the Deccan Traps, she says, can potentially help us understand where we’re heading.

    See the full article here .


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  • richardmitnick 11:20 am on February 15, 2019 Permalink | Reply
    Tags: "Physicists create a quantum refrigerator that cools with an absence of light", , , , Near-field photonic cooling through control of the chemical potential of photons, , , Science Magazine,   

    From U Michigan via Science Magazine: “Physicists create a quantum refrigerator that cools with an absence of light” 

    U Michigan bloc

    From University of Michigan

    via

    AAAS
    Science Magazine

    Feb. 14, 2019
    Daniel Garisto

    1
    This new device shows that an LED can cool other tiny objects. Joseph Xu/Michigan Engineering, Communications & Marketing

    For decades, atomic physicists have used laser light to slow atoms zinging around in a gas, cooling them to just above absolute zero to study their weird quantum properties. Now, a team of scientists has managed to similarly cool an object—but with the absence of light rather than its presence. The technique, which has never before been experimentally shown, might someday be used to chill the components in microelectronics.

    In an ordinary laser cooling experiment, physicists shine laser light from opposite directions—up, down, left, right, front, back—on a puff of gas such as rubidium. They tune the lasers precisely, so that if an atom moves toward one of them, it absorbs a photon and gets a gentle push back toward the center. Set it up just right and the light saps away the atoms’ kinetic energy, cooling the gas to a very low temperature.

    But Pramod Reddy, an applied physicist at the University of Michigan in Ann Arbor, wanted to try cooling without the special properties of laser light. He and colleagues started with a widget made of semiconducting material commonly found in video screens—a light-emitting diode (LED). An LED exploits a quantum mechanical effect to turn electrical energy into light. Roughly speaking, the LED acts like a little ramp for electrons. Apply a voltage in the right direction and it pushes electrons up and over the ramp, like kids on skateboards. As electrons fall over the ramp to a lower energy state, they emit photons.

    Crucially for the experiment, the LED emits no light when the voltage is reversed, as the electrons cannot go over the ramp in the opposite direction. In fact, reversing the voltage also suppresses the device’s infrared radiation—the broad spectrum of light (including heat) that you see when you look at a hot object through night vision goggles.

    That effectively makes the device colder—and it means the little thing can work like a microscopic refrigerator, Reddy says. All that’s necessary is to put it close enough to another tiny object, he says. “If you take a hot object and a cold object … you can have a radiative exchange of heat,” Reddy says. To prove that they could use an LED to cool, the scientists placed one just tens of nanometers—the width of a couple hundred atoms—away from a heat-measuring device called a calorimeter. That was close enough to increase the transfer of photons between the two objects, due to a process called quantum tunneling. Essentially, the gap was so small that photons could sometimes hop over it.

    The cooler LED absorbed more photons from the calorimeter than it gave back to it, wicking heat away from the calorimeter and lowering its temperature by a ten-thousandth of a degree Celsius, Reddy and colleagues report this week in Nature. That’s a small change, but given the tiny size of the LED, it equals an energy flux of 6 watts per square meter. For comparison, the sun provides about 1000 watts per square meter. Reddy and his colleagues believe they could someday increase the cooling flux up to that strength by reducing the gap size and siphoning away the heat that builds up in the LED.

    The technique probably won’t replace traditional refrigeration techniques or be able to cool materials below temperatures of about 60 K. But it has the potential to someday be used for cooling microelectronics, according to Shanhui Fan, a theoretical physicist at Stanford University in Palo Alto, California, who was not involved with the work. In earlier work, Fan used computer modeling to predict that an LED could have a sizeable cooling effect if placed nanometers from another object. Now, he said, Reddy and his team have realized that idea experimentally.

    See the full article here .


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    U MIchigan Campus

    The University of Michigan (U-M, UM, UMich, or U of M), frequently referred to simply as Michigan, is a public research university located in Ann Arbor, Michigan, United States. Originally, founded in 1817 in Detroit as the Catholepistemiad, or University of Michigania, 20 years before the Michigan Territory officially became a state, the University of Michigan is the state’s oldest university. The university moved to Ann Arbor in 1837 onto 40 acres (16 ha) of what is now known as Central Campus. Since its establishment in Ann Arbor, the university campus has expanded to include more than 584 major buildings with a combined area of more than 34 million gross square feet (781 acres or 3.16 km²), and has two satellite campuses located in Flint and Dearborn. The University was one of the founding members of the Association of American Universities.

    Considered one of the foremost research universities in the United States,[7] the university has very high research activity and its comprehensive graduate program offers doctoral degrees in the humanities, social sciences, and STEM fields (Science, Technology, Engineering and Mathematics) as well as professional degrees in business, medicine, law, pharmacy, nursing, social work and dentistry. Michigan’s body of living alumni (as of 2012) comprises more than 500,000. Besides academic life, Michigan’s athletic teams compete in Division I of the NCAA and are collectively known as the Wolverines. They are members of the Big Ten Conference.

     
  • richardmitnick 11:46 am on February 7, 2019 Permalink | Reply
    Tags: A costly and controversial space-based cosmic ray detector has found possible signs of dark matter, AMS began to measure the mass charge and energy of the billions of cosmic rays—charged particles from space—that pass down its maw, , , , , Officials in DOE's high energy physics program which funds the AMS's $4.5 million operating budget held a review to rank 13 ongoing projects. The AMS tied for last. The problem lay not with the experi, Positrons could come from the interactions of cosmic rays themselves, Samuel Ting a particle physicist at the Massachusetts Institute of Technology, Science Magazine, The AMS paper acknowledges that dark matter annihilation is just one possible explanation for the positrons, The space-based Alpha Magnetic Spectrometer on the ISS, Ting is also holding out for a different jaw-dropping discovery: heavy antimatter nuclei   

    From Science Magazine: “Space magnet homes in on clue to dark matter” 

    AAAS
    From Science Magazine

    Feb. 6, 2019
    Adrian Cho

    CERN Alpha Magnetic Spectrometer

    The space-based Alpha Magnetic Spectrometer on the ISS

    A costly and controversial space-based cosmic ray detector has found possible signs of dark matter, the invisible stuff thought to supply most of the universe’s mass. Or so says Samuel Ting, a particle physicist at the Massachusetts Institute of Technology in Cambridge and leader of the Alpha Magnetic Spectrometer (AMS), which is perched on the International Space Station (ISS).

    However, time is running out for the aging detector, and many researchers are skeptical about the dark matter interpretation, which Ting dances around with typical coyness. “If you listen to the storyline, it does sound like that’s where we’re headed, but we never quite get there,” says Angela Olinto, a cosmic ray physicist at the University of Chicago in Illinois.

    The co-winner of the 1976 Nobel Prize in Physics, Ting, 83, jetted around the world to drum up $1.5 billion for the AMS, and wooed NASA and the Department of Energy (DOE) into backing it. After astronauts bolted the 8500-kilogram, doughnut-shaped detector to the ISS in May 2011, it began to measure the mass, charge, and energy of the billions of cosmic rays—charged particles from space—that pass down its maw. Almost all of them are protons, electrons, and light nuclei such as helium, but a precious few consist of antimatter particles such as positrons. They stand out because, in the magnetic field of the AMS, their paths bend in the opposite direction from those of their matter counterparts.

    In 2014, AMS researchers reported an unexpected flux of positrons that kicked in at energies above 10 giga-electron volts (GeV) and seemed to fade by about 300 GeV. The excess could come from dark matter particles colliding and annihilating one another to produce electron-positron pairs, and the energy of the falloff might point to the mass of the dark matter particles. Now, with three times as many data, AMS researchers have clearly resolved that energy cutoff. The positron excess starts at 25 GeV and falls sharply at 284 GeV, the 227-member AMS team reported last week in Physical Review Letters. “It’s important because you do start to see a turnaround” in the energy spectrum, Olinto says. The cutoff is consistent with heavy dark matter particles with a mass of about 800 GeV, the researchers report.

    The AMS paper acknowledges that dark matter annihilation is just one possible explanation for the positrons. They could also come from a mundane astrophysical object, such as a pulsar—a spinning neutron star. But Ting emphasizes the steepness of the cutoff. “The cutoff also goes very quickly, very similar to [the signal from] dark matter collisions,” he says.

    In a third possibility, the positrons could come from the interactions of cosmic rays themselves. Cosmic ray protons emerging from remnants of supernova explosions regularly slam into atomic nuclei in interstellar space to create “secondary” cosmic rays, including positrons. AMS researchers say they’ve ruled out that explanation for the signal, because the proton collisions should produce a long tail in the positron spectrum instead of a sharp falloff. But Greg Tarlé, a cosmic ray physicist at the University of Michigan in Ann Arbor, says the AMS data reveal a telltale similarity between the energy spectrum of the positrons and that of the protons, supporting the idea that the protons are the source. “It’s the AMS data itself that give the best evidence for the positrons being secondaries,” Tarlé says.

    Every explanation for the positron excess has significant problems, cosmic ray experts say, but Ting insists the AMS may still sort it all out. The detector could run for the remaining life span of the ISS, perhaps until 2024. The AMS team will then have twice as many data, enough to tell whether the positron spectrum dives as steeply as dark matter scenarios predict, Ting says. Stephane Coutu, a physicist at Pennsylvania State University in University Park, disagrees. Doubling the data will shrink the error bars just 30%, he says, too little to resolve the issue. “They’re basically done,” Coutu says. “The rest is gilding a lily.”

    In May 2018, a federal advisory panel reached a similar conclusion. In 2017, the White House proposed slashing DOE’s research budget by 17%. In response, officials in DOE’s high energy physics program, which funds the AMS’s $4.5 million operating budget, held a review to rank 13 ongoing projects. The AMS tied for last. The problem lay not with the experiment, but with the theories to interpret its data, says Paul Grannis, a physicist at the State University of New York in Stony Brook who led the review. The theoretical uncertainties are “so big that anything you could do to improve the data will have very little impact,” Grannis says. In the end, Congress boosted the 2018 high energy physics budget by 10%, and DOE officials say they have no plans to cut the AMS.

    Ting is also holding out for a different jaw-dropping discovery: heavy antimatter nuclei. It would be huge because antinuclei heavier than a deuteron—a proton and a neutron—cannot be made in cosmic ray interactions and would have to originate in some region of the universe dominated by antimatter. Ting claims the AMS has captured a few antihelium nuclei [Science]. Coutu says a mountain of evidence already proves no antimatter regions exist, so the unpublished signals must be spurious, perhaps produced by misidentified helium nuclei.

    The antimatter claim, too, may remain untested. Despite last year’s reprieve, the AMS faces an uncertain future. Pumps that cool key detector components need replacing, and the fix will require a spacewalk, scheduled for October. “It’s no big deal,” Ting says, although he won’t guarantee success.

    If the AMS stops working, it will leave behind an outstanding legacy, even if it’s not the one Ting envisions. The detector has collected exquisite data on cosmic rays such as nuclei of helium, boron, beryllium, and carbon. The data are helping scientists understand what produces these ordinary cosmic rays, and how they journey through space. “The cosmic ray data that they’re producing is fantastic,” says Tarlé, often a vocal critic of Ting. “It wouldn’t have been done if Sam hadn’t convinced DOE and NASA to do it.”

    See the full article here .


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    Please help promote STEM in your local schools.

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  • richardmitnick 10:25 am on January 25, 2019 Permalink | Reply
    Tags: , , , , , , Science Magazine   

    From Science Magazine: “Missions expose surprising differences in the interiors of Saturn and Jupiter” 

    AAAS
    From Science Magazine

    Jan. 17, 2019
    Paul Voosen

    1
    Material thousands of kilometers below the clouds of Jupiter and Saturn tugs subtly on orbiting spacecraft, revealing hidden structure and motions.
    NASA/JPL/Space Science Institute.

    A clever use of radio signals from planetary spacecraft is allowing researchers to pierce the swirling clouds that hide the interiors of Jupiter and Saturn, where crushing pressure transforms matter into states unknown on Earth. The effort, led by Luciano Iess of Sapienza University in Rome, turned signals from two NASA probes, Cassini at Saturn and Juno at Jupiter, into probes of gravitational variations that originate deep inside these gas giants.

    What the researchers have found is fueling a high-stakes game of compare and contrast. The results, published last year in Nature for Jupiter and this week in Science for Saturn, show that “the two planets are more complex than we thought,” says Ravit Helled, a planetary scientist at the University of Zurich in Switzerland. “Giant planets are not simple balls of hydrogen and helium.”

    In the 1980s, Iess helped pioneer a radio instrument for Cassini that delivered an exceptionally clear signal because it worked in the Ka band, which is relatively free of noise from interplanetary plasma. By monitoring fluctuations in the signal, the team planned to search for gravitational waves from the cosmos and test general relativity during the spacecraft’s journey to Saturn, which began in 1997. Iess’s group put a similar device on Juno, which launched in 2011, but this time the aim was to study Jupiter’s interior.

    Juno skims close to Jupiter’s surface every 53 days, and with each pass hidden influences inside the planet exert a minute pull on the spacecraft, resulting in tiny Doppler shifts in its radio signals. Initially, Iess and his team thought measuring those shifts wouldn’t be feasible at Saturn because of the gravitational influence of its rings. But that obstacle disappeared earlier this decade, after the Cassini team decided to end the mission by sending the craft on a series of orbits, dubbed the Grand Finale, that dipped below the rings and eliminated their effects. As a result, Iess and colleagues could use radio fluctuations to map the shape of gravity fields at both planets, allowing them to infer the density and movements of material deep inside.

    One goal was to probe the roots of the powerful winds that whip clouds on the gas giants into distinct horizontal bands. Scientists assumed the winds would either be shallow, like winds on Earth, or very deep, penetrating tens of thousands of kilometers into the planets, where extreme pressure is expected to rip the electrons from hydrogen, turning it into a metallike conductor. The results for Jupiter were a puzzle: The 500-kilometer-per-hour winds aren’t shallow, but they reach just 3000 kilometers into the planet, some 4% of its radius. Saturn then delivered a different mystery: Despite its smaller volume, its surface winds, which top out at 1800 kilometers per hour, go three times deeper, to at least 9000 kilometers. “Everybody was caught by surprise,” Iess says.

    Scientists think the explanation for both findings lies in the planets’ deep magnetic fields. At pressures of about 100,000 times that of Earth’s atmosphere—well short of those that create metallic hydrogen—hydrogen partially ionizes, turning it into a semiconductor. That allows the magnetic field to control the movement of the material, preventing it from crossing the field lines. “The magnetic field freezes the flow,” and the planet becomes rigid, says Yohai Kaspi, a planetary scientist at the Weizmann Institute of Science in Rehovot, Israel, who worked with Iess. Jupiter has three times Saturn’s mass, which causes a far more rapid increase in atmospheric pressure—about three times faster. “It’s basically the same result,” says Kaspi, but the rigidity sets in at a shallower depth.

    The Juno and Cassini data yield only faint clues about greater depths. Scientists once believed the gas giants formed much like Earth, building up a rocky core before vacuuming gas from the protoplanetary disc. Such a stately process would have likely led to distinct layers, including a discrete core enriched in heavier elements. But Juno’s measurements, interpreted through models, suggested Jupiter’s core has only a fuzzy boundary, its heavy elements tapering off for up to half its radius. This suggests that rather than forming a rocky core and then adding gas, Jupiter might have taken shape from vaporized rock and gas right from the start, says Nadine Nettelmann, a planetary scientist at the University of Rostock in Germany.

    The picture is still murkier for Saturn. Cassini data hint that its core could have a mass of some 15 to 18 times that of Earth, with a higher concentration of heavy elements than Jupiter’s, which could suggest a clearer boundary. But that interpretation is tentative, says David Stevenson, a planetary scientist at the California Institute of Technology in Pasadena and a co-investigator on Juno. What’s more, Cassini was tugged by something deep within Saturn that could not be explained by the winds, Iess says. “We call it the dark side of Saturn’s gravity.” Whatever is causing this tug, Stevenson adds, it’s not found on Jupiter. “It is a major result. I don’t think we understand it yet.”

    Because Cassini’s mission ended with the Grand Finale, which culminated with the probe’s destruction in Saturn’s atmosphere, “There’s not going to be a better measurement anytime soon,” says Chris Mankovich, a planetary scientist at the University of California, Santa Cruz. But although the rings complicated the gravity measurements, they also offer an opportunity. For some unknown reason—perhaps its winds, perhaps the pull of its many moons—Saturn vibrates. The gravitational influence of those oscillations minutely warps the shape of its rings into a pattern like the spiraling arms of a galaxy. The result is a visible record of the vibrations, like the trace on a seismograph, which scientists can decipher to plumb the planet. Mankovich says it’s clear that some of these vibrations reach the deep interior, and he has already used “ring seismology” to estimate how fast Saturn’s interior rotates.

    Cassini’s last gift may be to show how fortunate scientists are to have the rings as probes. Data from the spacecraft’s final orbits enabled Iess’s team to show the rings are low in mass, which means they must be young, as little as 10 million years old—otherwise, encroaching interplanetary soot would have darkened them. They continue to rain material onto Saturn, the Cassini team has found, which could one day lead to their demise. But for now they stand brilliant against the gas giant, with more stories to tell.

    See the full article here .


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  • richardmitnick 1:42 pm on January 2, 2019 Permalink | Reply
    Tags: , , , , Breathtaking touchdown, , , Science Magazine   

    From Science Magazine: “Japan’s asteroid mission faces ‘breathtaking’ touchdown” 

    AAAS
    From Science Magazine

    Jan. 2, 2019
    Dennis Normile

    1
    Hayabusa2 imaged its shadow during a rehearsal descent. JAXA

    JAXA/Hayabusa 2 Credit: JAXA/Akihiro Ikeshita

    Japan’s Hayabusa mission made history in 2010 for bringing back to Earth the first samples ever collected on an asteroid. But the 7-year, 4-billion-kilometer odyssey was marked by degraded solar panels, innumerable mechanical failures, and a fuel explosion that knocked the spacecraft into a tumble and cut communications with ground control for 2 months. When planning its encore, Hayabusa2, Japan’s scientists and engineers were determined to avoid such drama. They made components more robust, enhanced communications capabilities, and thoroughly tested new technologies.

    But the target asteroid, Ryugu, had fresh surprises in store. “By looking at the details of every asteroid ever studied, we had expected to find at least some wide flat area suitable for a landing,” says Yuichi Tsuda, Hayabusa2’s project manager at the Japan Aerospace Exploration Agency’s Institute of Space and Astronautical Science (ISAS), which is headquartered in Sagamihara. Instead, when the spacecraft reached Ryugu in June 2018—at 290 million kilometers from Earth—it found a cragged, cratered, boulder-strewn surface that makes landing a daunting challenge. The first sampling touchdown, scheduled for October, was postponed until at least the end of this month, and at a symposium here on 21 and 22 December, ISAS engineers presented an audacious new plan to make a pinpoint landing between closely spaced boulders. “It’s breathtaking,” says Bruce Damer, an origins of life researcher at the University of California, Santa Cruz.

    Yet most everything else has gone according to plan since Hayabusa2 was launched in December 2014. Its cameras and detectors have already provided clues to the asteroid’s mass, density, and mineral and elemental composition, and three rovers dropped on the asteroid have examined the surface. At the symposium, ISAS researchers presented early results, including evidence of an abundance of organic material and hints that the asteroid’s parent body once held water. Those findings “add to the evidence that asteroids rather than comets brought water and organic materials to Earth,” says project scientist Seiichiro Watanabe of Nagoya University in Japan.

    Ryugu is 1 kilometer across and 900 meters top to bottom, with a notable bulge around the equator, like a diamond. Visible light observations and computer modeling suggest it’s a porous pile of rubble that likely agglomerated dust, rocks, and boulders after another asteroid or planetesimal slammed into its parent body during the early days of the solar system. Ryugu spins around its own axis once every 7.6 hours, but simulations suggest that during the early phase of its formation, it had a rotation period of only 3.5 hours. That probably produced the bulge, by causing surface landslides or pushing material outward from the core, Watanabe says. Analyzing surface material from the equator in an Earth-based laboratory could offer support for one of those scenarios, he adds. If the sample has been exposed to space weathering for a long time, it was likely moved there by landslides; if it is relatively fresh, it probably migrated from the asteroid’s interior.

    So far, Hayabusa2 has not detected water on or near Ryugu’s surface. But its infrared spectrometer has found signs of hydroxide-bearing minerals that suggest water once existed either on the parent body or on the asteroid, says Mutsumi Komatsu, a planetary materials scientist at the Graduate University for Advanced Studies in Hayama, Japan. The asteroid’s high porosity also suggests it once harbored significant amounts of water or ice and other volatile compounds that later escaped, Watanabe says. Asteroids such as Ryugu are rich in carbon as well, and they may have been responsible for bringing both water and carbon, life’s key building block, to a rocky Earth early in its history. (Comets, by contrast, are just 3% to 5% carbon.)

    Support for that theory, known as the late heavy bombardment, comes from another asteroid sample return mission now in progress. Early last month, NASA’s OSIRISREx reached asteroid Bennu, which is shaped like a spinning top as well and, the U.S. space agency has reported, has water trapped in the soil. “We’re lucky to be able to conduct comparative studies of these two asteroid brothers,” Watanabe says.

    Geologist Stephen Mojzsis of the University of Colorado in Boulder is not convinced such asteroids will prove to be the source of Earth’s water; there are other theories, he says, including the possibility that a giant Jupiter-like gaseous planet migrated from the outer to the inner solar system, bringing water and other molecules with it around the time Earth was formed. Still, findings on Ryugu’s shape and composition “scientifically, could be very important,” he says.

    Some new details come from up-close looks at the asteroid’s surface. On 21 September, Hayabusa2 dropped a pair of rovers the size of a birthday cake, named Minerva-II1A and -II1B, on Ryugu’s northern hemisphere. Taking advantage of its low gravity to hop autonomously, they take pictures that have revealed “microscopic features of the surface,” Tsuda says. And on 5 October, Hayabusa2 released a rover developed by the German and French space agencies that analyzed soil samples in situ and returned additional pictures.

    The ultimate objective, to bring asteroid samples back to Earth, will allow lab studies that can reveal much more about the asteroid’s age and content. ISAS engineers programmed the craft to perform autonomous landings, anticipating safe touchdown zones at least 100 meters in diameter. Instead, the biggest safe area within the first landing zone turned out to be just 12 meters wide.

    That will complicate what was already a nail-biting operation. Prior to each landing, Hayabusa2 planned to drop a small sphere sheathed in a highly reflective material to be used as a target, to ensure the craft is moving in sync with the asteroid’s rotation. Gravity then pulls the craft down gently until a collection horn extending from its underside makes contact with the asteroid; after a bulletlike projectile is fired into the surface, soil and rock fragments hopefully ricochet into a catcher within the horn. For safety, the craft has to steer clear of rocks larger than 70 centimeters.

    During a rehearsal in late October, Hayabusa2 released a target marker above the 12-meter safe circle; unfortunately, it came to rest more than 10 meters outside the zone. But it is just 2.9 meters away from the edge of a second possible landing site that’s 6 meters in diameter. Engineers now plan to have the craft first hover above the target marker and then move laterally to be above the center of one of the two sites. Because the navigation camera points straight down, the target marker will be outside the camera’s field of view as Hayabusa2 descends, leaving the craft to navigate on its own.

    “We are now in the process of selecting which landing site” to aim for, says Fuyuto Terui, who is in charge of mission guidance, navigation, and control. Aiming at the smaller zone means Hayabusa2 can keep the target marker in sight until the craft is close to the surface; the bigger zone gives more leeway for error, but the craft will lose its view of the marker earlier in the descent.

    Assuming the craft survives the first landing, plans call for Hayabusa2 to blast a 2-meter-deep crater into Ryugu’s surface at another site a few months later, by hitting it with a 2-kilogram, copper projectile. This is expected to expose subsurface material for observations by the craft’s cameras and sensors; the spacecraft may collect some material from the crater as well, using the same horn device. There could be a third touchdown, elsewhere on the asteroid. If all goes well, Hayabusa2 will make it back to Earth with its treasures in 2020.

    See the full article here .


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  • richardmitnick 12:14 pm on December 19, 2018 Permalink | Reply
    Tags: , Discovery of recent Antarctic ice sheet collapse raises fears of a new global flood, , Glaciologists worry about the present-day stability of the West Antarctic Ice Sheet, Science Magazine   

    From Science Magazine: “Discovery of recent Antarctic ice sheet collapse raises fears of a new global flood” 

    AAAS
    From Science Magazine

    Dec. 18, 2018
    Paul Voosen

    1
    A 30-kilometer crack angles across the Pine Island Glacier, a vulnerable part of the West Antarctic Ice Sheet. NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team/Flickr

    Some 125,000 years ago, during the last brief warm period between ice ages, Earth was awash. Temperatures during this time, called the Eemian, were barely higher than in today’s greenhouse-warmed world. Yet proxy records show sea levels were 6 to 9 meters higher than they are today, drowning huge swaths of what is now dry land.

    Scientists have now identified the source of all that water: a collapse of the West Antarctic Ice Sheet. Glaciologists worry about the present-day stability of this formidable ice mass. Its base lies below sea level, at risk of being undermined by warming ocean waters, and glaciers fringing it are retreating fast. The discovery, teased out of a sediment core and reported last week at a meeting of the American Geophysical Union in Washington, D.C., validates those concerns, providing evidence that the ice sheet disappeared in the recent geological past under climate conditions similar to today’s. “We had an absence of evidence,” says Anders Carlson, a glacial geologist at Oregon State University in Corvallis, who led the work. “I think we have evidence of absence now.”

    If it holds up, the finding would confirm that “the West Antarctic Ice Sheet might not need a huge nudge to budge,” says Jeremy Shakun, a paleoclimatologist at Boston College. That, in turn, suggests “the big uptick in mass loss observed there in the past decade or two is perhaps the start of that process rather than a short-term blip.” If so, the world may need to prepare for sea level to rise farther and faster than expected: Once the ancient ice sheet collapse got going, some records suggest, ocean waters rose as fast as some 2.5 meters per century.

    As an analogy for the present, the Eemian, from 129,000 to 116,000 years ago, is “probably the best there is, but it’s not great,” says Jacqueline Austermann, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory. Global temperatures were some 2°C above preindustrial levels (compared with 1°C today). But the cause of the warming was not greenhouse gases, but slight changes in Earth’s orbit and spin axis, and Antarctica was probably cooler than today. What drove the sea level rise, recorded by fossil corals now marooned well above high tide, has been a mystery.

    Scientists once blamed the melting of Greenland’s ice sheet. But in 2011, Carlson and colleagues exonerated Greenland after identifying isotopic fingerprints of its bedrock in sediment from an ocean core drilled off its southern tip. The isotopes showed ice continued to grind away at the bedrock through the Eemian. If the Greenland Ice Sheet didn’t vanish and push up sea level, the vulnerable West Antarctic Ice Sheet was the obvious suspect. But the suspicion rested on little more than simple subtraction, Shakun says. “It’s not exactly the most compelling or satisfying argument.”

    Carlson and his team set out to apply their isotope technique to Antarctica. First, they drew on archived marine sediment cores drilled from along the edge of the western ice sheet. Studying 29 cores, they identified geochemical signatures for three different bedrock source regions: the mountainous Antarctic Peninsula; the Amundsen province, close to the Ross Sea; and the area in between, around the particularly vulnerable Pine Island Glacier.

    Armed with these fingerprints, Carlson’s team then analyzed marine sediments from a single archived core, drilled farther offshore in the Bellingshausen Sea, west of the Antarctic Peninsula. A stable current runs along the West Antarctic continental shelf, picking up ice-eroded silt along the way. The current dumps much of this silt near the core’s site, where it builds up fast and traps shelled microorganisms called foraminifera, which can be dated by comparing their oxygen isotope ratios to those in cores with known dates. Over a stretch of 10 meters, the core contained 140,000 years of built-up silt.

    For most of that period, the silt contained geochemical signatures from all three of the West Antarctic bedrock regions, the team reported, suggesting continuous ice-driven erosion. But in a section dated to the early Eemian, the fingerprints winked out: first from the Pine Island Glacier, then from the Amundsen province. That left only silt from the mountainous peninsula, where glaciers may have persisted. “We don’t see any sediments coming from the much larger West Antarctic Ice Sheet, which we’d interpret to mean that it was gone. It didn’t have that erosive power anymore,” Carlson says.

    He concedes that the dating of the core is not precise, which means the pause in erosion may not have taken place during the Eemian. It is also possible that the pause itself is illusory—that ocean currents temporarily shifted, sweeping silt to another site.

    More certainty is on the way. Next month, the International Ocean Discovery Program’s JOIDES Resolution research ship will begin a 3-month voyage to drill at least five marine cores off West Antarctica.

    2
    JOIDES Resolution research ship

    “That’s going to be a great test,” Carlson says. Meanwhile, he hopes to get his own study published in time to be included in the next United Nations climate report. In the 2001 and 2007 reports, West Antarctic collapse was not even considered in estimates of future sea level; only in 2013 did authors start to talk about an Antarctic surprise, he says. Research is due by December 2019. “We gotta beat that deadline.”

    See the full article here .


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