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  • richardmitnick 1:42 pm on July 29, 2015 Permalink | Reply
    Tags: , , Brown Dwarfs, Caltech   

    From Caltech: “”Failed Stars” Host Powerful Auroral Displays” 

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    Caltech

    07/29/2015
    Kimm Fesenmaier

    1
    Artist’s impression of an auroral display on a brown dwarf. Credit: Chuck Carter and Gregg Hallinan/Caltech

    Brown dwarfs are relatively cool, dim objects that are difficult to detect and hard to classify. They are too massive to be planets, yet possess some planetlike characteristics; they are too small to sustain hydrogen fusion reactions at their cores, a defining characteristic of stars, yet they have starlike attributes.

    By observing a brown dwarf 20 light-years away using both radio and optical telescopes, a team led by Gregg Hallinan, assistant professor of astronomy at Caltech, has found another feature that makes these so-called failed stars more like supersized planets—they host powerful auroras near their magnetic poles.

    The findings appear in the July 30 issue of the journal Nature.

    “We’re finding that brown dwarfs are not like small stars in terms of their magnetic activity; they’re like giant planets with hugely powerful auroras,” says Hallinan. “If you were able to stand on the surface of the brown dwarf we observed—something you could never do because of its extremely hot temperatures and crushing surface gravity—you would sometimes be treated to a fantastic light show courtesy of auroras hundreds of thousands of times more powerful than any detected in our solar system.”

    In the early 2000s, astronomers began finding that brown dwarfs emit radio waves. At first, everyone assumed that the brown dwarfs were creating the radio waves in basically the same way that stars do—through the action of an extremely hot atmosphere, or corona, heated by magnetic activity near the object’s surface. But brown dwarfs do not generate large flares and charged-particle emissions in the way that our sun and other stars do, so the radio emissions were surprising.

    While in graduate school, in 2006, Hallinan discovered that brown dwarfs can actually pulse at radio frequencies. “We see a similar pulsing phenomenon from planets in our solar system,” says Hallinan, “and that radio emission is actually due to auroras.” Since then he has wondered if the radio emissions seen on brown dwarfs might be caused by auroras.

    Auroral displays result when charged particles, carried by the stellar wind for example, manage to enter a planet’s magnetosphere, the region where such charged particles are influenced by the planet’s magnetic field. Once within the magnetosphere, those particles get accelerated along the planet’s magnetic field lines to the planet’s poles, where they collide with gas atoms in the atmosphere and produce the bright emissions associated with auroras.

    Following his hunch, Hallinan and his colleagues conducted an extensive observation campaign of a brown dwarf called LSRJ 1835+3259, using the National Radio Astronomy Observatory’s Very Large Array (VLA), the most powerful radio telescope in the world, as well as optical instruments that included Palomar’s Hale Telescope and the W. M. Keck Observatory’s telescopes.

    NRAO VLA
    NRAO/VLA

    Caltech Palomar 200 inch Hale Telescope
    Caltech Palomar 200 inch Hale Telescope interior
    Caltech Palomar Observatory

    Keck Observatory
    Keck Observatory Interior
    Keck Observatory

    Using the VLA they detected a bright pulse of radio waves that appeared as the brown dwarf rotated around. The object rotates every 2.84 hours, so the researchers were able to watch nearly three full rotations over the course of a single night.

    Next, the astronomers used the Hale Telescope to observe that the brown dwarf varied optically on the same period as the radio pulses. Focusing on one of the spectral lines associated with excited hydrogen—the h-alpha emission line—they found that the object’s brightness varied periodically.

    Finally, Hallinan and his colleagues used the Keck telescopes to measure precisely the brightness of the brown dwarf over time—no simple feat given that these objects are many thousands of times fainter than our own sun. Hallinan and his team were able to establish that this hydrogen emission is a signature of auroras near the surface of the brown dwarf.

    “As the electrons spiral down toward the atmosphere, they produce radio emissions, and then when they hit the atmosphere, they excite hydrogen in a process that occurs at Earth and other planets, albeit tens of thousands of times more intense,” explains Hallinan. “We now know that this kind of auroral behavior is extending all the way from planets up to brown dwarfs.”

    In the case of brown dwarfs, charged particles cannot be driven into their magnetosphere by a stellar wind, as there is no stellar wind to do so. Hallinan says that some other source, such as an orbiting planet moving through the brown dwarf’s magnetosphere, may be generating a current and producing the auroras. “But until we map the aurora accurately, we won’t be able to say where it’s coming from,” he says.

    He notes that brown dwarfs offer a convenient stepping stone to studying exoplanets, planets orbiting stars other than our own sun. “For the coolest brown dwarfs we’ve discovered, their atmosphere is pretty similar to what we would expect for many exoplanets, and you can actually look at a brown dwarf and study its atmosphere without having a star nearby that’s a factor of a million times brighter obscuring your observations,” says Hallinan.

    Just as he has used measurements of radio waves to determine the strength of magnetic fields around brown dwarfs, he hopes to use the low-frequency radio observations of the newly built Owens Valley Long Wavelength Array to measure the magnetic fields of exoplanets.

    Caltech Owens Radio Observatory
    Caltech Owens Valley Radio Observatory

    “That could be particularly interesting because whether or not a planet has a magnetic field may be an important factor in habitability,” he says. “I’m trying to build a picture of magnetic field strength and topology and the role that magnetic fields play as we go from stars to brown dwarfs and eventually right down into the planetary regime.”

    The work, Magnetospherically driven optical and radio aurorae at the end of the main sequence, was supported by funding from the National Science Foundation. Additional authors on the paper include Caltech senior postdoctoral scholar Stephen Bourke, Caltech graduate students Sebastian Pineda and Melodie Kao, Leon Harding of JPL, Stuart Littlefair of the University of Sheffield, Garret Cotter of the University of Oxford, Ray Butler of National University of Ireland, Galway, Aaron Golden of Yeshiva University, Gibor Basri of UC Berkeley, Gerry Doyle of Armagh Observatory, Svetlana Berdyugina of the Kiepenheuer Institute for Solar Physics, Alexey Kuznetsov of the Institute of Solar-Terrestrial Physics in Irkutsk, Russia, Michael Rupen of the National Radio Astronomy Observatory, and Antoaneta Antonova of Sofia University.

    See the full article here.

    Please help promote STEM in your local schools.

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 2:51 pm on July 20, 2015 Permalink | Reply
    Tags: , Caltech, ,   

    From Caltech: “Freezing a Bullet (+)” 

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    Caltech

    July 20, 2015
    Kimm Fesenmaier
    jnalick

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    Crystal structure of the assembly chaperone of ribosomal protein L4 (Acl4) that picks up a newly synthesized ribosomal protein when it emerges from the ribosome in the cytoplasm, protects it from the degradation machinery, and delivers it to the assembly site of new ribosomes in the nucleus. Credit: Ferdinand Huber/Caltech

    X-Ray Vision, an article in our Spring 2015 issue, examined the central role Caltech has played in developing a powerful technique for revealing the molecular machinery of life. In May, chemist André Hoeltz, who was featured in the article, published a new paper describing how he used the technique to reveal how protein-synthesizing cellular machines are built.

    Ribosomes are vital to the function of all living cells. Using the genetic information from RNA, these large molecular complexes build proteins by linking amino acids together in a specific order. Scientists have known for more than half a century that these cellular machines are themselves made up of about 80 different proteins, called ribosomal proteins, along with several RNA molecules and that these components are added in a particular sequence to construct new ribosomes, but no one has known the mechanism that controls that process.

    Now researchers from Caltech and Heidelberg University have combined their expertise to track a ribosomal protein in yeast all the way from its synthesis in the cytoplasm, the cellular compartment surrounding the nucleus of a cell, to its incorporation into a developing ribosome within the nucleus. In so doing, they have identified a new chaperone protein, known as Acl4, that ushers a specific ribosomal protein through the construction process and a new regulatory mechanism that likely occurs in all eukaryotic cells.

    The results, described in a paper that appears online in the journal Molecular Cell, also suggest an approach for making new antifungal agents.

    The work was completed in the labs of André Hoelz, assistant professor of chemistry at Caltech, and Ed Hurt, director of the Heidelberg University Biochemistry Center (BZH).

    “We now understand how this chaperone, Acl4, works with its ribosomal protein with great precision,” says Hoelz. “Seeing that is kind of like being able to freeze a bullet whizzing through the air and turn it around and analyze it in all dimensions to see exactly what it looks like.”

    That is because the entire ribosome assembly process—including the synthesis of new ribosomal proteins by ribosomes in the cytoplasm, the transfer of those proteins into the nucleus, their incorporation into a developing ribosome, and the completed ribosome’s export back out of the nucleus into the cytoplasm—happens in the tens of minutes timescale. So quickly that more than a million ribosomes are produced per day in mammalian cells to allow for turnover and cell division. Therefore, being able to follow a ribosomal protein through that process is not a simple task.

    Hurt and his team in Germany have developed a new technique to capture the state of a ribosomal protein shortly after it is synthesized. When they “stopped” this particular flying bullet, an important ribosomal protein known as L4, they found that its was bound to Acl4.

    Hoelz’s group at Caltech then used X-ray crystallography to obtain an atomic snapshot of Acl4 and further biochemical interaction studies to establish how Acl4 recognizes and protects L4. They found that Acl4 attaches to L4 (having a high affinity for only that ribosomal protein) as it emerges from the ribosome that produced it, akin to a hand gripping a baseball. Thereby the chaperone ensures that the ribosomal protein is protected from machinery in the cell that would otherwise destroy it and ushers the L4 molecule through the sole gateway between the nucleus and cytoplasm, called the nuclear pore complex, to the site in the nucleus where new ribosomes are constructed.

    “The ribosomal protein together with its chaperone basically travel through the nucleus and screen their surroundings until they find an assembling ribosome that is at exactly the right stage for the ribosomal protein to be incorporated,” explains Ferdinand Huber, a graduate student in Hoelz’s group and one of the first authors on the paper. “Once found, the chaperone lets the ribosomal protein go and gets recycled to go pick up another protein.”

    The researchers say that Acl4 is just one example from a whole family of chaperone proteins that likely work in this same fashion.

    Hoelz adds that if this process does not work properly, ribosomes and proteins cannot be made. Some diseases (including aggressive leukemia subtypes) are associated with malfunctions in this process.

    “It is likely that human cells also contain a dedicated assembly chaperone for L4. However, we are certain that it has a distinct atomic structure, which might allow us to develop new antifungal agents,” Hoelz says. “By preventing the chaperone from interacting with its partner, you could keep the cell from making new ribosomes. You could potentially weaken the organism to the point where the immune system could then clear the infection. This is a completely new approach.”

    Co-first authors on the paper, Coordinated Ribosomal L4 Protein Assembly into the Pre-Ribosome Is Regulated by Its Eukaryote-Specific Extension, are Huber and Philipp Stelter of Heidelberg University. Additional authors include Ruth Kunze and Dirk Flemming also from Heidelberg University. The work was supported by the Boehringer Ingelheim Fonds, the V Foundation for Cancer Research, the Edward Mallinckrodt, Jr. Foundation, the Sidney Kimmel Foundation for Cancer Research, and the German Research Foundation (DFG).

    See the full article here.

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 10:47 am on June 4, 2015 Permalink | Reply
    Tags: , , Caltech, CARMA Array,   

    From Caltech: “Celebrating 11 Years of CARMA Discoveries” 

    Caltech Logo
    Caltech

    06/03/2015
    Ker Than

    CARMA Array
    CARMA Array

    For more than a decade, large, moveable telescopes tucked away on a remote, high-altitude site in the Inyo Mountains, about 250 miles northeast of Los Angeles, have worked together to paint a picture of the universe through radio-wave observations.

    Known as the Combined Array for Research in Millimeter-wave Astronomy, or CARMA, the telescopes formed one of the most powerful millimeter interferometers in the world. CARMA was created in 2004 through the merger of the Owens Valley Radio Observatory (OVRO) Millimeter Array and the Berkeley Illinois Maryland Association (BIMA) Array and initially consisted of 15 telescopes. In 2008, the University of Chicago joined CARMA, increasing the telescope count to 23.

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    An artist’s depiction of a gamma ray burst, the most powerful explosive event in the universe. CARMA detected the millimeter-wavelength emission from the afterglow of the gamma ray burst 130427A only 18 hours after it first exploded on April 27, 2013. The CARMA observations revealed a surprise: in addition to the forward moving shock, CARMA showed the presence of a backward moving shock, or “reverse” shock, that had long been predicted, but never conclusively observed until now. Credit: Gemini Observatory/AURA, artwork by Lynette Cook

    CARMA’s higher elevation, improved electronics, and greater number of connected antennae enabled more precise observations of radio emission from molecules and cold dust across the universe, leading to ground-breaking studies that encompass a range of cosmic objects and phenomena—including stellar birth, early planet formation, supermassive black holes, galaxies, galaxy mergers, and sudden, unexpected events such as gamma-ray bursts and supernova explosions.

    “Over its lifetime, it has moved well beyond its initial goals both scientifically and technically,” says Anneila Sargent (MS ’67, PhD ’78, both degrees in astronomy), the Ira S. Bowen Professor of Astronomy at Caltech and the first director of CARMA.

    On April 3, CARMA probed the skies for the last time. The project ceased operations and its telescopes will be repurposed and integrated into other survey projects.

    Here is a look back at some of CARMA’s most significant discoveries and contributions to the field of astronomy.

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    These CARMA images highlight the range of morphologies observed in circumstellar disks, which may indicate that the disks are in different stages in the planet formation process, or that they are evolving along distinct pathways. The bottom row highlights the disk around the star LkCa 15, where CARMA detected a 40 AU diameter inner hole. The two-color Keck image (bottom right) reveals an infrared source along the inner edge of this hole. The infrared luminosity is consistent with a 6M Jupiter planet, which may have cleared the hole.
    Credit: CARMA

    Planet Formation

    Newly formed stars are surrounded by a rotating disk of gas and dust, known as a circumstellar disk. These disks provide the building materials for planetary systems like our own solar system, and can contain important clues about the planet formation process.

    During its operation, CARMA imaged disks around dozens of young stars such as RY Tau and DG Tau. The observations revealed that circumstellar disks often are larger in size than our solar system and contain enough material to form Jupiter-size planets. Interestingly, these disks exhibit a variety of morphologies, and scientists think the different shapes reflect different stages or pathways of the planet formation process.

    CARMA also helped gather evidence that supported planet formation theories by capturing some of the first images of gaps in circumstellar disks. According to conventional wisdom, planets can form in disks when stars are as young as half a million years old. Computer models show that if these so-called protoplanets are the size of Jupiter or larger, they should carve out gaps or holes in the rings through gravitational interactions with the disk material. In 2012, the team of OVRO executive director John Carpenter reported using CARMA to observe one such gap in the disk surrounding the young star LkCa 15. Observations by the Keck Observatory in Hawaii revealed an infrared source along the inner edge of the gap that was consistent with a planet that has six times the mass of Jupiter.

    Keck Observatory
    Keck

    “Until ALMA”—the Atacama Large Millimeter/submillimeter Array in Chile, a billion-dollar international collaboration involving the United States, Europe, and Japan—”came along, CARMA produced the highest-resolution images of circumstellar disks at millimeter wavelengths,” says Carpenter.

    ALMA Array
    ALMA

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    A color image of the Whirlpool galaxy M51 from the Hubble Space Telescope (HST). A three composite of images taken at wavelengths of 4350 Angstroms (blue), 5550 Angstroms (green), and 6580 Angstroms (red). Bright regions in the red color are the regions of recent massive star formation, where ultraviolet photons from the massive stars ionize the surrounding gas which radiates the hydrogen recombination line emission. Dark lanes run along spiral arms, indicating the location where the dense interstellar medium is abundant.
    Credit: Jin Koda

    Star Formation

    Stars form in “clouds” of gas, consisting primarily of molecular hydrogen, that contain as much as a million times the mass of the sun. “We do not understand yet how the diffuse molecular gas distributed over large scales flows to the small dense regions that ultimately form stars,” Carpenter says.

    Magnetic fields may play a key role in the star formation process, but obtaining observations of these fields, especially on small scales, is challenging. Using CARMA, astronomers were able to chart the direction of the magnetic field in the dense material that surrounds newly formed protostars by mapping the polarized thermal radiation from dust grains in molecular clouds. A CARMA survey of the polarized dust emission from 29 sources showed that magnetic fields in the dense gas are randomly aligned with outflowing gas entrained by jets from the protostars.

    If the outflows emerge along the rotation axes of circumstellar disks, as has been observed in a few cases, the results suggest that, contrary to theoretical expectations, the circumstellar disks are not aligned with the fields in the dense gas from which they formed. “We don’t know the punch line—are magnetic fields critical in the star formation process or not?—because, as always, the observations just raise more questions,” Carpenter admits. “But the CARMA observations are pointing the direction for further observations with ALMA.”

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    CARMA was used to image molecular gas in the nearby Andromeda galaxy. All stars form in dense clouds of molecular gas and thus to understand star formation it is important to analyze the properties of molecular clouds.
    Credit: Andreas Schruba

    Molecular gas in galaxies

    The molecular gas in galaxies is the raw material for star formation. “Being able to study how much gas there is in a galaxy, how it’s converted to stars, and at what rate is very important for understanding how galaxies evolve over time,” Carpenter says.

    By resolving the molecular gas reservoirs in local galaxies and measuring the mass of gas in distant galaxies that existed when the cosmos was a fraction of its current age, CARMA made fundamental contributions to understanding the processes that shape the observable universe.

    For example, CARMA revealed the evolution, in the spiral galaxy M51, of giant molecular clouds (GMCs) driven by large-scale galactic structure and dynamics. CARMA was used to show that giant molecular clouds grow through coalescence and then break up into smaller clouds that may again come together in the future. Furthermore, the process can occur multiple times over a cloud’s lifetime. This new picture of molecular cloud evolution is more complex than previous scenarios, which treated the clouds as discrete objects that dissolved back into the atomic interstellar medium after a certain period of time. “CARMA’s imaging capability showed the full cycle of GMCs’ dynamical evolution for the first time,” Carpenter says.

    The Milky Way’s black hole

    CARMA worked as a standalone array, but it was also able to function as part of very-long-baseline interferometry (VLBI), in which astronomical radio signals are gathered from multiple radio telescopes on Earth to create higher-resolution images than is possible with single telescopes working alone.

    In this fashion, CARMA has been linked together with the Submillimeter Telescope in Arizona and the James Clerk Maxwell Telescope and Submillimeter Array in Hawaii to paint one of the most detailed pictures to date of the monstrous black hole at the heart of our Milky Way galaxy. The combined observations achieved an angular resolution of 40 microarcseconds—the equivalent of seeing a tennis ball on the moon.

    “If you just used CARMA alone, then the best resolution you would get is 0.15 arcseconds. So VLBI improved the resolution by a factor of 3,750,” Carpenter says.

    Astronomers have used the VLBI technique to successfully detect radio signals emitted from gas orbiting just outside of this supermassive black hole’s event horizon, the radius around the black hole where gravity is so strong that even light cannot escape. “These observations measured the size of the emitting region around the black hole and placed constraints on the accretion disk that is feeding the black hole,” he explains.

    In other work, VLBI observations showed that the black hole at the center of M87, a giant elliptical galaxy, is spinning.

    Transients

    CARMA also played an important role in following up “transients,” objects that unexpectedly burst into existence and then dim and fade equally rapidly (on an astronomical timescale), over periods from seconds to years. Some transients can be attributed to powerful cosmic explosions such as gamma-ray bursts (GRBs) or supernovas, but the mechanisms by which they originate remain unexplained.

    “By looking at transients at different wavelengths—and, in particular, looking at them soon after they are discovered—we can understand the progenitors that are causing these bursts,” says Carpenter, who notes that CARMA led the field in observations of these events at millimeter wavelengths. Indeed, on April 27, 2013, CARMA detected the millimeter-wavelength emission from the afterglow of GRB 130427A only 18 hours after it first exploded.

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    GRB 130427A Before and after in 100+ MeV light

    The CARMA observations revealed a surprise: in addition to the forward-moving shock, there was one moving backward. This “reverse” shock had long been predicted, but never conclusively observed.

    Getting data on such unpredictable transient events is difficult at many observatories, because of logistics and the complexity of scheduling. “Targets of opportunity require flexibility on the part of the organization to respond to an event when it happens,” says Sterl Phinney (BS ’80, astronomy), professor of theoretical astrophysics and executive officer for astronomy and astrophysics at Caltech. “CARMA was excellent for this purpose, because it was so nimble.”

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    Multi-wavelength view of the redshift z=0.2 cluster MS0735+7421. Left to right: CARMA observations of the SZ effect, X-ray data from Chandra, radio data from the VLA, and a three-color composite of the three. The SZ image reveals a large-scale distortion of the intra-cluster medium coincident with X-ray cavities produced by a massive AGN outflow, an example of the wide dynamic-range, multi-wavelength cluster imaging enabled by CARMA. Credit: Erik Leitch (University of Chicago, Owens Valley Radio Observatory)

    Galaxy clusters

    Galaxy clusters are the largest gravitationally bound objects in the universe. CARMA studied galaxy clusters by taking advantage of a phenomenon known as the Sunyaev-Zel’dovich (SZ) effect. The SZ effect results when primordial radiation left over from the Big Bang, known as the cosmic microwave background (CMB), is scattered to higher energies after interacting with the hot ionized gas that permeates galaxy clusters. Using CARMA, astronomers recently confirmed a galaxy cluster candidate at redshifts of 1.75 and 1.9, making them the two most distant clusters for which an SZ effect has been measured.

    “CARMA can detect the distortion in the CMB spectrum,” Carpenter says. “We’ve observed over 100 clusters at very good resolution. These data have been very important to calibrating the relation between the SZ signal and the cluster mass, probing the structure of clusters, and helping discover the most distant clusters known in the universe.”

    Training the next generation

    In addition to its many scientific contributions, CARMA also served as an important teaching facility for the next generation of astronomers. About 300 graduate students and postdoctoral researchers have cut their teeth on interferometry astronomy at CARMA over the years. “They were able to get hands-on experience in millimeter-wave astronomy at the observatory, something that is becoming more and more rare these days,” Sargent says.

    Tom Soifer (BS ’68, physics), professor of physics and Kent and Joyce Kresa Leadership Chair of the Division of Physics, Mathematics and Astronomy, notes that many of those trainees now hold prestigious positions at the National Radio Astronomy Observatory (NRAO) or are professors at universities across the country, where they educate future scientists and engineers and help with the North American ALMA effort. “The United States is currently part of a tripartite international collaboration that operates ALMA. Most of the North American ALMA team trained either at CARMA or the Caltech OVRO Millimeter Array, CARMA’s precursor,” he says.

    Looking ahead

    Following CARMA’s shutdown, the Cedar Flats sites will be restored to prior conditions, and the telescopes will be moved to OVRO. Although the astronomers closest to the observatory find the closure disappointing, Phinney takes a broader view, seeing the shutdown as part of the steady march of progress in astronomy. “CARMA was the cutting edge of high-frequency astronomy for the past decade. Now that mantle has passed to the global facility called ALMA, and Caltech will take on new frontiers.”

    Indeed, Caltech continues to push the technological frontier of astronomy through other projects. For example, Caltech Assistant Professor of Astronomy Greg Hallinan is leading the effort to build a Long Wavelength Array (LWA) station at OVRO that will instantaneously image the entire viewable sky every few seconds at low-frequency wavelengths to search for radio transients.

    The success of CARMA and OVRO, Soifer says, gives him confidence that the LWA will also be successful. “We have a tremendously capable group of scientists and engineers. If anybody can make this challenging enterprise work, they can.”

    See the full article here.

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 7:59 am on May 27, 2015 Permalink | Reply
    Tags: , Caltech,   

    From Caltech: “Using Radar Satellites to Study Icelandic Volcanoes and Glaciers” 

    Caltech Logo
    Caltech

    05/26/2015
    Kimm Fesenmaier

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    This Landsat 8 image, acquired on September 6, 2014, is a false-color view of the Holuhraun lava field north of Vatnajökull glacier in Iceland. The image combines shortwave infrared, near infrared, and green light to distinguish between cooler ice and steam and hot extruded lava. The Bárðarbunga caldera, visible in the lower left of the image under the ice cap, experienced a large-scale collapse starting in mid-August. Credit: USGS

    NASA LandSat 8
    Landsat 8

    On August 16 of last year, Mark Simons, a professor of geophysics at Caltech, landed in Reykjavik with 15 students and two other faculty members to begin leading a tour of the volcanic, tectonic, and glaciological highlights of Iceland. That same day, a swarm of earthquakes began shaking the island nation—seismicity that was related to one of Iceland’s many volcanoes, Bárðarbunga caldera, which lies beneath Vatnajökull ice cap.

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    Bárðarbunga

    As the trip proceeded, it became clear to scientists studying the event that magma beneath the caldera was feeding a dyke, a vertical sheet of magma slicing through the crust in a northeasterly direction. On August 29, as the Caltech group departed Iceland, the dike triggered an eruption in a lava field called Holuhraun, about 40 kilometers (roughly 25 miles) from the caldera just beyond the northern limit of the ice cap.

    Although the timing of the volcanic activity necessitated some shuffling of the trip’s activities, such as canceling planned overnight visits near what was soon to become the eruption zone, it was also scientifically fortuitous. Simons is one of the leaders of a Caltech/JPL project known as the Advanced Rapid Imaging and Analysis (ARIA) program, which aims to use a growing constellation of international imaging radar satellites that will improve situational awareness, and thus response, following natural disasters. Under the ARIA umbrella, Caltech and JPL/NASA had already formed a collaboration with the Italian Space Agency (ASI) to use its COSMO-SkyMed (CSK) constellation (consisting of four orbiting X-Band radar satellites) following such events.

    Through the ASI/ARIA collaboration, the managers of CSK agreed to target the activity at Bárðarbunga for imaging using a technique called interferometric synthetic aperture radar (InSAR). As two CSK satellites flew over, separated by just one day, they bounced signals off the ground to create images of the surface of the glacier above the caldera. By comparing those two images in what is called an interferogram, the scientists could see how the glacier surface had moved during that intervening day. By the evening of August 28, Simons was able to pull up that first interferogram on his cell phone. It showed that the ice above the caldera was subsiding at a rate of 50 centimeters (more than a foot and a half) a day—a clear indication that the magma chamber below Bárðarbunga caldera was deflating.

    The next morning, before his return flight to the United States, Simons took the data to researchers at the University of Iceland who were tracking Bárðarbunga’s activity.

    “At that point, there had been no recognition that the caldera was collapsing. Naturally, they were focused on the dyke and all the earthquakes to the north,” says Simons. “Our goal was just to let them know about the activity at the caldera because we were really worried about the possibility of triggering a subglacial melt event that would generate a catastrophic flood.”

    Luckily, that flood never happened, but the researchers at the University of Iceland did ramp up observations of the caldera with radar altimetry flights and installed a continuous GPS station on the ice overlying the center of the caldera.

    Last December, Icelandic researchers published a paper in Nature about the Bárðarbunga event, largely focusing on the dyke and eruption. Now, completing the picture, Simons and his colleagues have developed a model to describe the collapsing caldera and the earthquakes produced by that action. The new findings appear in the journal Geophysical Journal International.

    “Over a span of two months, there were more than 50 magnitude-5 earthquakes in this area. But they didn’t look like regular faulting—like shearing a crack,” says Simons. “Instead, the earthquakes looked like they resulted from movement inward along a vertical axis and horizontally outward in a radial direction—like an aluminum can when it’s being crushed.”

    To try to determine what was actually generating the unusual earthquakes, Bryan Riel, a graduate student in Simons’s group and lead author on the paper, used the original one-day interferogram of the Bárðarbunga area along with four others collected by CSK in September and October. Most of those one-day pairs spanned at least one of the earthquakes, but in a couple of cases, they did not. That allowed Riel to isolate the effect of the earthquakes and determine that most of the subsidence of the ice was due to what is called aseismic activity—the kind that does not produce big earthquakes. Thus, Riel was able to show that the earthquakes were not the primary cause of the surface deformation inferred from the satellite radar data.

    “What we know for sure is that the magma chamber was deflating as the magma was feeding the dyke going northward,” says Riel. “We have come up with two different models to explain what was actually generating the earthquakes.”

    In the first scenario, because the magma chamber deflated, pressure from the overlying rock and ice caused the caldera to collapse, producing the unusual earthquakes. This mechanism has been observed in cases of collapsing mines (e.g., the Crandall Canyon Mine in Utah).

    The second model hypothesizes that there is a ring fault arcing around a significant portion of the caldera. As the magma chamber deflated, the large block of rock above it dropped but periodically got stuck on portions of the ring fault. As the block became unstuck, it caused rapid slip on the curved fault, producing the unusual earthquakes.

    “Because we had access to these satellite images as well as GPS data, we have been able to produce two potential interpretations for the collapse of a caldera—a rare event that occurs maybe once every 50 to 100 years,” says Simons. “To be able to see this documented as it’s happening is truly phenomenal.”

    Additional authors on the paper, The collapse of Bárðarbunga caldera, Iceland, are Hiroo Kanamori, John E. and Hazel S. Smits Professor of Geophysics, Emeritus, at Caltech; Pietro Milillo of the University of Basilicata in Potenza, Italy; Paul Lundgren of JPL; and Sergey Samsonov of the Canada Centre for Mapping and Earth Observation. The work was supported by a NASA Earth and Space Science Fellowship and by the Caltech/JPL President’s and Director’s Fund.

    See the full article here.

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 8:42 pm on May 11, 2015 Permalink | Reply
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    From JPL: “Astronomers Take a New Kind of Pulse From the Sky” 

    JPL

    May 11, 2015
    Media Contact
    Whitney Clavin
    Jet Propulsion Laboratory, Pasadena, Calif.
    818-354-4673
    whitney.clavin@jpl.nasa.gov

    Fast Facts:

    › Enormous telescope array produces videos of flickering, flashing night sky

    › Produces 5,000 DVDs worth of data every day

    Every night, our sky beats with the pulses of radio light waves, most of which go unseen. A new array of radio antennas in California, called the Owens Valley Long Wavelength Array, is gearing up to catch some of this action, aiming to pick up signals from flaring stars, flashing planets and potentially even more exotic objects.

    The array has already produced a new video of the radio sky, showing how it flickers and morphs over 24 hours.

    “Our new telescope lets us see the entire sky all at once, and we can image everything instantaneously,” said Gregg Hallinan, an assistant professor of astronomy at the California Institute of Technology in Pasadena, and the principal investigator of the Owens Valley Long Wavelength Array.

    One of the key goals of the project is to monitor extrasolar space weather — the interaction between nearby stars and their orbiting planets. Our sun flares with radiation and hurtles particles and magnetic fields outward. Spectacular light displays, or auroras, are produced on the planets in our solar system when those particles interact with chemical elements in the planets’ atmospheres. The same is true for stars beyond our sun, and, if those stars have planets, they too would, in theory, have auroras.

    Measurements of these interactions in other star systems could reveal new information about the strength of planets’ magnetic fields — and thus their potential for harboring life. Magnetic fields were a critical factor in the development of life on Earth, offering protection from dangerous radiation and particles.

    The radio antennas, which combine to form a powerful radio telescope, are based at Caltech’s Owens Valley Radio Observatory, near Big Pine, California. Other partners include: NASA’s Jet Propulsion Laboratory, Pasadena, California; Harvard University, Cambridge, Massachusetts; the University of New Mexico, Albuquerque; Virginia Tech, Blacksburg; and the U.S. Naval Research Laboratory, headquartered in Washington.

    NASA JPL Owens Valley Low Frequency Radio Observatory
    JPL Caltech Owens Valley Low Frequency Radio Observatory

    The array’s station consists of 250 low-cost antennas, each about 3 feet (1 meter) in size, spread out in the Owens Valley. Future plans include thousands of additional antennas; the more antennas in the array, the greater the image sensitivity. The small size of the antennas has benefits as well, leading to a huge field of view in the same way that binoculars can see a large patch of sky. The array covers the entire viewable sky all at once.

    “Just as the antenna of your car radio can detect local radio stations no matter where they are around the car, these antennas can detect signals anywhere in the sky,” said Joseph Lazio, an astronomer on the project from JPL.

    The Owens Valley Long Wavelength Array might also be able to gather traces of radio light from the very first stars and galaxies.

    “The biggest challenge is that this weak radiation from the early universe is obscured by the radio emission from our own Milky Way galaxy, which is about a million times brighter than the signal itself, so you have to have very carefully calibrated data to see it,” said Hallinan. “That’s one of the primary goals of our collaboration — to try to get the first statistical measure of that weak signal from our cosmic dawn.”

    Lazio said the array will help in the design of future space missions. Some radio wavelengths are blocked or reflected off Earth’s atmosphere, but in space the whole radio spectrum can be observed.

    “Ultimately, we will likely need to construct a similar array of simple antennas and put it in space, or on the moon,” he said.

    One challenge of a project like this is managing the deluge of data. The array produces more than 5,000 DVDs worth of data every day. A supercomputer developed by a group led by Lincoln Greenhill of Harvard University for the National Science Foundation-funded Large-Aperture Experiment to Detect the Dark Ages delivers this torrent of data. It uses graphics processing units similar to those used in modern computer games to combine signals from all the antennas in real time. These combined signals are then sent to a second computer cluster, the All-Sky Transient Monitor, developed at Caltech and JPL, which produces all-sky images in real-time.

    The project is funded by Caltech, JPL, NASA and the National Science Foundation.

    A more detailed feature story about the project from Caltech is online at:

    http://www.caltech.edu/news/powerful-new-radio-telescope-array-searches-entire-sky-247-46754

    More information on the Long Wavelength Array is also online at:

    http://lwa.unm.edu

    See the full article here.

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    NASA JPL Campus

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

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  • richardmitnick 1:52 pm on April 13, 2015 Permalink | Reply
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    From Caltech: “Explaining Saturn’s Great White Spots” 

    Caltech Logo
    Caltech

    04/13/2015
    Kathy Svitil

    1
    This image, taken by NASA’s Cassini spacecraft in February 2011, shows a huge storm in Saturn’s northern hemisphere.
    Credit: NASA/JPL-Caltech/Space Science Institute

    Every 20 to 30 years, Saturn’s atmosphere roils with giant, planet-encircling thunderstorms that produce intense lightning and enormous cloud disturbances. The head of one of these storms—popularly called “great white spots,” in analogy to the Great Red Spot of Jupiter—can be as large as Earth. Unlike Jupiter’s spot, which is calm at the center and has no lightning, the Saturn spots are active in the center and have long tails that eventually wrap around the planet.

    Six such storms have been observed on Saturn over the past 140 years, alternating between the equator and midlatitudes, with the most recent emerging in December 2010 and encircling the planet within six months. The storms usually occur when Saturn’s northern hemisphere is most tilted toward the sun. Just what triggers them and why they occur so infrequently, however, has been unclear.

    Now, a new study by two Caltech planetary scientists suggests a possible cause for these storms. The study was published April 13 in the advance online issue of the journal Nature Geoscience.

    Using numerical modeling, Professor of Planetary Science Andrew Ingersoll and his graduate student Cheng Li simulated the formation of the storms and found that they may be caused by the weight of the water molecules in the planet’s atmosphere. Because these water molecules are heavy compared to the hydrogen and helium that comprise most of the gas-giant planet’s atmosphere, they make the upper atmosphere lighter when they rain out, and that suppresses convection.

    Over time, this leads to a cooling of the upper atmosphere. But that cooling eventually overrides the suppressed convection, and warm moist air rapidly rises and triggers a thunderstorm. “The upper atmosphere is so cold and so massive that it takes 20 to 30 years for this cooling to trigger another storm,” says Ingersoll.

    Ingersoll and Li found that this mechanism matches observations of the great white spot of 2010 taken by NASA’s Cassini spacecraft, which has been observing Saturn and its moons since 2004.

    NASA Cassini Spacecraft
    Cassini

    The researchers also propose that the absence of planet-encircling storms on Jupiter could be explained if Jupiter’s atmosphere contains less water vapor than Saturn’s atmosphere. That is because saturated gas (gas that contains the maximum amount of moisture that it can hold at a particular temperature) in a hydrogen-helium atmosphere goes through a density minimum as it cools. That is, it first becomes less dense as the water precipitates out, and then it becomes more dense as cooling proceeds further. “Going through that minimum is key to suppressing the convection, but there has to be enough water vapor to start with,” says Li.

    Ingersoll and Li note that observations by the Galileo spacecraft and the Hubble Space Telescope indicate that Saturn does indeed have enough water to go through this density minimum, whereas Jupiter does not. In November 2016, NASA’s Juno spacecraft, now en route to Jupiter, will start measuring the water abundance on that planet. “That should help us understand not only the meteorology but also the planet’s formation, since water is expected to be the third most abundant molecule after hydrogen and helium in a giant planet atmosphere,” Ingersoll says.

    NASA Galileo
    Galileo

    NASA Hubble Telescope
    NASA/ESA Hubble

    NASA Juno
    Juno

    The work in the paper, Moist convection in hydrogen atmospheres and the frequency of Saturn’s giant storms, was supported by the National Science Foundation and the Cassini Project of NASA.

    See the full article here.

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 2:02 pm on March 30, 2015 Permalink | Reply
    Tags: , , Caltech, , , NANOGrave,   

    From Caltech: “New NSF-Funded Physics Frontiers Center Expands Hunt for Gravitational Waves” 

    Caltech Logo
    Caltech

    03/30/2015
    Kathy Svitil

    1
    Gravitational waves are ripples in space-time (represented by the green grid) produced by interacting supermassive black holes in distant galaxies. As these waves wash over the Milky Way, they cause minute yet measurable changes in the arrival times at Earth of the radio signals from pulsars, the Universe’s most stable natural clocks. These telltale changes can be detected by sensitive radio telescopes, like the Arecibo Observatory in Puerto Rico and the Green Bank Telescope in West Virginia. Credit: David Champion

    The search for gravitational waves—elusive ripples in the fabric of space-time predicted to arise from extremely energetic and large-scale cosmic events such as the collisions of neutron stars and black holes—has expanded, thanks to a $14.5-million, five-year award from the National Science Foundation for the creation and operation of a multi-institution Physics Frontiers Center (PFC) called the North American Nanohertz Observatory for Gravitational Waves (NANOGrav).

    The NANOGrav PFC will be directed by Xavier Siemens, a physicist at the University of Wisconsin–Milwaukee and the principal investigator for the project, and will fund the NANOGrav research activities of 55 scientists and students distributed across the 15-institution collaboration, including the work of four Caltech/JPL scientists—Senior Faculty Associate Curt Cutler; Visiting Associates Joseph Lazio and Michele Vallisneri; and Walid Majid, a visiting associate at Caltech and a JPL research scientist—as well as two new postdoctoral fellows at Caltech to be supported by the PFC funds. JPL is managed by Caltech for NASA.

    “Caltech has a long tradition of leadership in both the theoretical prediction of sources of gravitational waves and experimental searches for them,” says Sterl Phinney, professor of theoretical astrophysics and executive officer for astronomy in the Division of Physics, Mathematics and Astronomy. “This ranges from waves created during the inflation of the early universe, which have periods of billions of years; to waves from supermassive black hole binaries in the nuclei of galaxies, with periods of years; to a multitude of sources with periods of minutes to hours; to the final inspiraling of neutron stars and stellar mass black holes, which create gravitational waves with periods less than a tenth of a second.”

    The detection of the high-frequency gravitational waves created in this last set of events is a central goal of Advanced LIGO (the next-generation Laser Interferometry Gravitational-Wave Observatory), scheduled to begin operation later in 2015. LIGO and Advanced LIGO, funded by NSF, are comanaged by Caltech and MIT.

    “This new Physics Frontier Center is a significant boost to what has long been the dark horse in the exploration of the spectrum of gravitational waves: low-frequency gravitational waves,” Phinney says. These gravitational waves are predicted to have such a long wavelength—significantly larger than our solar system—that we cannot build a detector large enough to observe them. Fortunately, the universe itself has created its own detection tool, millisecond pulsars—the rapidly spinning, superdense remains of massive stars that have exploded as supernovas. These ultrastable stars appear to “tick” every time their beamed emissions sweep past Earth like a lighthouse beacon. Gravitational waves may be detected in the small but perceptible fluctuations—a few tens of nanoseconds over five or more years—they cause in the measured arrival times at Earth of radio pulses from these millisecond pulsars.

    NANOGrav makes use of the Arecibo Observatory in Puerto Rico and the National Radio Astronomy Observatory’s Green Bank Telescope (GBT), and will obtain other data from telescopes in Europe, Australia, and Canada. The team of researchers at Caltech will lead NANOGrav’s efforts to develop the approaches and algorithms for extracting the weak gravitational-wave signals from the minute changes in the arrival times of pulses from radio pulsars that are observed regularly by these instruments.

    Arecibo Observatory
    Arecibo Radio Observatory Telescope

    NRAO GBT
    NRAO/GBT

    See the full article here.

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 5:17 am on March 24, 2015 Permalink | Reply
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    From Caltech: “New Research Suggests Solar System May Have Once Harbored Super-Earths” 

    Caltech Logo
    Caltech

    03/23/2015
    Kimm Fesenmaier

    Caltech and UC Santa Cruz Researchers Say Earth Belongs to a Second Generation of Planets

    1
    This snapshot from a new simulation depicts a time early in the solar system’s history when Jupiter likely made a grand inward migration (here, Jupiter’s orbit is the thick white circle). As it moved inward, Jupiter picked up primitive planetary building blocks, or planetesimals, and drove them into eccentric orbits (turquoise) that overlapped the unperturbed part of the planetary disk (yellow), setting off a cascade of collisions that would have ushered any interior planets into the sun.
    Credit: K.Batygin/Caltech

    Long before Mercury, Venus, Earth, and Mars formed, it seems that the inner solar system may have harbored a number of super-Earths—planets larger than Earth but smaller than Neptune. If so, those planets are long gone—broken up and fallen into the sun billions of years ago largely due to a great inward-and-then-outward journey that Jupiter made early in the solar system’s history.

    This possible scenario has been suggested by Konstantin Batygin, a Caltech planetary scientist, and Gregory Laughlin of UC Santa Cruz in a paper that appears the week of March 23 in the online edition of the Proceedings of the National Academy of Sciences (PNAS). The results of their calculations and simulations suggest the possibility of a new picture of the early solar system that would help to answer a number of outstanding questions about the current makeup of the solar system and of Earth itself. For example, the new work addresses why the terrestrial planets in our solar system have such relatively low masses compared to the planets orbiting other sun-like stars.

    “Our work suggests that Jupiter’s inward-outward migration could have destroyed a first generation of planets and set the stage for the formation of the mass-depleted terrestrial planets that our solar system has today,” says Batygin, an assistant professor of planetary science. “All of this fits beautifully with other recent developments in understanding how the solar system evolved, while filling in some gaps.”

    Thanks to recent surveys of exoplanets—planets in solar systems other than our own—we know that about half of sun-like stars in our galactic neighborhood have orbiting planets. Yet those systems look nothing like our own. In our solar system, very little lies within Mercury’s orbit; there is only a little debris—probably near-Earth asteroids that moved further inward—but certainly no planets. That is in sharp contrast with what astronomers see in most planetary systems. These systems typically have one or more planets that are substantially more massive than Earth orbiting closer to their suns than Mercury does, but very few objects at distances beyond.

    “Indeed, it appears that the solar system today is not the common representative of the galactic planetary census. Instead we are something of an outlier,” says Batygin. “But there is no reason to think that the dominant mode of planet formation throughout the galaxy should not have occurred here. It is more likely that subsequent changes have altered its original makeup.”

    According to Batygin and Laughlin, Jupiter is critical to understanding how the solar system came to be the way it is today. Their model incorporates something known as the Grand Tack scenario, which was first posed in 2001 by a group at Queen Mary University of London and subsequently revisited in 2011 by a team at the Nice Observatory. That scenario says that during the first few million years of the solar system’s lifetime, when planetary bodies were still embedded in a disk of gas and dust around a relatively young sun, Jupiter became so massive and gravitationally influential that it was able to clear a gap in the disk. And as the sun pulled the disk’s gas in toward itself, Jupiter also began drifting inward, as though carried on a giant conveyor belt.

    “Jupiter would have continued on that belt, eventually being dumped onto the sun if not for Saturn,” explains Batygin. Saturn formed after Jupiter but got pulled toward the sun at a faster rate, allowing it to catch up. Once the two massive planets got close enough, they locked into a special kind of relationship called an orbital resonance, where their orbital periods were rational—that is, expressible as a ratio of whole numbers. In a 2:1 orbital resonance, for example, Saturn would complete two orbits around the sun in the same amount of time that it took Jupiter to make a single orbit. In such a relationship, the two bodies would begin to exert a gravitational influence on one another.

    “That resonance allowed the two planets to open up a mutual gap in the disk, and they started playing this game where they traded angular momentum and energy with one another, almost to a beat,” says Batygin. Eventually, that back and forth would have caused all of the gas between the two worlds to be pushed out, a situation that would have reversed the planets’ migration direction and sent them back outward in the solar system. (Hence, the “tack” part of the Grand Tack scenario: the planets migrate inward and then change course dramatically, something like a boat tacking around a buoy.)

    In an earlier model developed by Bradley Hansen at UCLA, the terrestrial planets conveniently end up in their current orbits with their current masses under a particular set of circumstances—one in which all of the inner solar system’s planetary building blocks, or planetesimals, happen to populate a narrow ring stretching from 0.7 to 1 astronomical unit (1 astronomical unit is the average distance from the sun to Earth), 10 million years after the sun’s formation. According to the Grand Tack scenario, the outer edge of that ring would have been delineated by Jupiter as it moved toward the sun on its conveyor belt and cleared a gap in the disk all the way to Earth’s current orbit.

    But what about the inner edge? Why should the planetesimals be limited to the ring on the inside? “That point had not been addressed,” says Batygin.

    He says the answer could lie in primordial super-Earths. The empty hole of the inner solar system corresponds almost exactly to the orbital neighborhood where super-Earths are typically found around other stars. It is therefore reasonable to speculate that this region was cleared out in the primordial solar system by a group of first-generation planets that did not survive.

    Batygin and Laughlin’s calculations and simulations show that as Jupiter moved inward, it pulled all the planetesimals it encountered along the way into orbital resonances and carried them toward the sun. But as those planetesimals got closer to the sun, their orbits also became elliptical. “You cannot reduce the size of your orbit without paying a price, and that turns out to be increased ellipticity,” explains Batygin. Those new, more elongated orbits caused the planetesimals, mostly on the order of 100 kilometers in radius, to sweep through previously unpenetrated regions of the disk, setting off a cascade of collisions among the debris. In fact, Batygin’s calculations show that during this period, every planetesimal would have collided with another object at least once every 200 years, violently breaking them apart and sending them decaying into the sun at an increased rate.

    The researchers did one final simulation to see what would happen to a population of super-Earths in the inner solar system if they were around when this cascade of collisions started. They ran the simulation on a well-known extrasolar system known as Kepler-11, which features six super-Earths with a combined mass 40 times that of Earth, orbiting a sun-like star. The result? The model predicts that the super-Earths would be shepherded into the sun by a decaying avalanche of planetesimals over a period of 20,000 years.

    “It’s a very effective physical process,” says Batygin. “You only need a few Earth masses worth of material to drive tens of Earth masses worth of planets into the sun.”

    Batygin notes that when Jupiter tacked around, some fraction of the planetesimals it was carrying with it would have calmed back down into circular orbits. Only about 10 percent of the material Jupiter swept up would need to be left behind to account for the mass that now makes up Mercury, Venus, Earth, and Mars.

    From that point, it would take millions of years for those planetesimals to clump together and eventually form the terrestrial planets—a scenario that fits nicely with measurements that suggest that Earth formed 100–200 million years after the birth of the sun. Since the primordial disk of hydrogen and helium gas would have been long gone by that time, this could also explain why Earth lacks a hydrogen atmosphere. “We formed from this volatile-depleted debris,” says Batygin.

    And that sets us apart in another way from the majority of exoplanets. Batygin expects that most exoplanets—which are mostly super-Earths—have substantial hydrogen atmospheres, because they formed at a point in the evolution of their planetary disk when the gas would have still been abundant. “Ultimately, what this means is that planets truly like Earth are intrinsically not very common,” he says.

    The paper also suggests that the formation of gas giant planets such as Jupiter and Saturn—a process that planetary scientists believe is relatively rare—plays a major role in determining whether a planetary system winds up looking something like our own or like the more typical systems with close-in super-Earths. As planet hunters identify additional systems that harbor gas giants, Batygin and Laughlin will have more data against which they can check their hypothesis—to see just how often other migrating giant planets set off collisional cascades in their planetary systems, sending primordial super-Earths into their host stars.

    The researchers describe their work in a paper titled Jupiter’s Decisive Role in the Inner Solar System’s Early Evolution.

    See the full article here.

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  • richardmitnick 3:52 pm on March 9, 2015 Permalink | Reply
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    From Caltech: “One Step Closer to Artificial Photosynthesis and “Solar Fuels” 

    Caltech Logo
    Caltech

    03/09/2015
    Ker Than

    1
    Ke Sun, a Caltech postdoc in the lab of George L. Argyros Professor and Professor of Chemistry Nate Lewis, peers into a sample of a new, protective film that he has helped develop to aid in the process of harnessing sunlight to generate fuels.
    Credit: Lance Hayashida/Caltech Marcomm

    Caltech scientists, inspired by a chemical process found in leaves, have developed an electrically conductive film that could help pave the way for devices capable of harnessing sunlight to split water into hydrogen fuel.

    When applied to semiconducting materials such as silicon, the nickel oxide film prevents rust buildup and facilitates an important chemical process in the solar-driven production of fuels such as methane or hydrogen.

    “We have developed a new type of protective coating that enables a key process in the solar-driven production of fuels to be performed with record efficiency, stability, and effectiveness, and in a system that is intrinsically safe and does not produce explosive mixtures of hydrogen and oxygen,” says Nate Lewis, the George L. Argyros Professor and professor of chemistry at Caltech and a coauthor of a new study, published the week of March 9 in the online issue of the journal the Proceedings of the National Academy of Sciences, that describes the film.

    The development could help lead to safe, efficient artificial photosynthetic systems—also called solar-fuel generators or “artificial leaves”—that replicate the natural process of photosynthesis that plants use to convert sunlight, water, and carbon dioxide into oxygen and fuel in the form of carbohydrates, or sugars.

    The artificial leaf that Lewis’ team is developing in part at Caltech’s Joint Center for Artificial Photosynthesis (JCAP) consists of three main components: two electrodes—a photoanode and a photocathode—and a membrane. The photoanode uses sunlight to oxidize water molecules to generate oxygen gas, protons, and electrons, while the photocathode recombines the protons and electrons to form hydrogen gas. The membrane, which is typically made of plastic, keeps the two gases separate in order to eliminate any possibility of an explosion, and lets the gas be collected under pressure to safely push it into a pipeline.

    Scientists have tried building the electrodes out of common semiconductors such as silicon or gallium arsenide—which absorb light and are also used in solar panels—but a major problem is that these materials develop an oxide layer (that is, rust) when exposed to water.

    Lewis and other scientists have experimented with creating protective coatings for the electrodes, but all previous attempts have failed for various reasons. “You want the coating to be many things: chemically compatible with the semiconductor it’s trying to protect, impermeable to water, electrically conductive, highly transparent to incoming light, and highly catalytic for the reaction to make oxygen and fuels,” says Lewis, who is also JCAP’s scientific director. “Creating a protective layer that displayed any one of these attributes would be a significant leap forward, but what we’ve now discovered is a material that can do all of these things at once.”

    The team has shown that its nickel oxide film is compatible with many different kinds of semiconductor materials, including silicon, indium phosphide, and cadmium telluride. When applied to photoanodes, the nickel oxide film far exceeded the performance of other similar films—including one that Lewis’s group created just last year. That film was more complicated—it consisted of two layers versus one and used as its main ingredient titanium dioxide (TiO2, also known as titania), a naturally occurring compound that is also used to make sunscreens, toothpastes, and white paint.

    “After watching the photoanodes run at record performance without any noticeable degradation for 24 hours, and then 100 hours, and then 500 hours, I knew we had done what scientists had failed to do before,” says Ke Sun, a postdoc in Lewis’s lab and the first author of the new study.

    Lewis’s team developed a technique for creating the nickel oxide film that involves smashing atoms of argon into a pellet of nickel atoms at high speeds, in an oxygen-rich environment. “The nickel fragments that sputter off of the pellet react with the oxygen atoms to produce an oxidized form of nickel that gets deposited onto the semiconductor,” Lewis says.

    Crucially, the team’s nickel oxide film works well in conjunction with the membrane that separates the photoanode from the photocathode and staggers the production of hydrogen and oxygen gases.

    “Without a membrane, the photoanode and photocathode are close enough to each other to conduct electricity, and if you also have bubbles of highly reactive hydrogen and oxygen gases being produced in the same place at the same time, that is a recipe for disaster,” Lewis says. “With our film, you can build a safe device that will not explode, and that lasts and is efficient, all at once.”

    Lewis cautions that scientists are still a long way off from developing a commercial product that can convert sunlight into fuel. Other components of the system, such as the photocathode, will also need to be perfected.

    “Our team is also working on a photocathode,” Lewis says. “What we have to do is combine both of these elements together and show that the entire system works. That will not be easy, but we now have one of the missing key pieces that has eluded the field for the past half-century.”

    Along with Lewis and Sun, additional authors on the paper, “Stable solar-driven oxidation of water by semiconducting photoanodes protected by transparent catalytic nickel oxide films,” include Caltech graduate students Fadl Saadi, Michael Lichterman, Xinghao Zhou, Noah Plymale, and Stefan Omelchenko; William Hale, from the University of Southampton; Hsin-Ping Wang and Jr-Hau He, from King Abdullah University in Saudi Arabia; Kimberly Papadantonakis, a scientific research manager at Caltech; and Bruce Brunschwig, the director of the Molecular Materials Research Center at Caltech. Funding was provided by the Office of Science at the U.S. Department of Energy, the National Science Foundation, the Beckman Institute, and the Gordon and Betty Moore Foundation.

    See the full article here.

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  • richardmitnick 3:19 pm on February 13, 2015 Permalink | Reply
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    From Caltech: “How Iron Feels the Heat” 

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    Caltech

    02/13/2015
    Jessica Stoller-Conrad

    1

    As you heat up a piece of iron, the arrangement of the iron atoms changes several times before melting. This unusual behavior is one reason why steel, in which iron plays a starring role, is so sturdy and ubiquitous in everything from teapots to skyscrapers. But the details of just how and why iron takes on so many different forms have remained a mystery. Recent work at Caltech in the Division of Engineering and Applied Science, however, provides evidence for how iron’s magnetism plays a role in this curious property—an understanding that could help researchers develop better and stronger steel.

    “Humans have been working with regular old iron for thousands of years, but this is a piece about its thermodynamics that no one has ever really understood,” says Brent Fultz, the Barbara and Stanley R. Rawn, Jr., Professor of Materials Science and Applied Physics.

    The laws of thermodynamics govern the natural behavior of materials, such as the temperature at which water boils and the timing of chemical reactions. These same principles also determine how atoms in solids are arranged, and in the case of iron, nature changes its mind several times at high temperatures. At room temperature, the iron atoms are in an unusual loosely packed open arrangement; as iron is heated past 912 degrees Celsius, the atoms become more closely packed before loosening again at 1,394 degrees Celsius and ultimately melting at 1,538 degrees Celsius.

    Iron is magnetic at room temperature, and previous work predicted that iron’s magnetism favors its open structure at low temperatures, but at 770 degrees Celsius iron loses its magnetism. However, iron maintains its open structure for more than a hundred degrees beyond this magnetic transition. This led the researchers to believe that there must be something else contributing to iron’s unusual thermodynamic properties.

    For this missing link, graduate student Lisa Mauger and her colleagues needed to turn up the heat. Solids store heat as small atomic vibrations—vibrations that create disorder, or entropy. At high temperatures, entropy dominates thermodynamics, and atomic vibrations are the largest source of entropy in iron. By studying how these vibrations change as the temperature goes up and magnetism is lost, the researchers hoped to learn more about what is driving these structural rearrangements.

    To do this, the team took its samples of iron to the High Pressure Collaborative Access Team beamline of the Advanced Photon Source [APS] at Argonne National Laboratory [ANL] in Argonne, Illinois. This synchrotron facility produces intense flashes of x-rays that can be tuned to detect the quantum particles of atomic vibration—called phonon excitations—in iron.

    ANL APS
    ANL APS interior
    APS at ANL

    When coupling these vibrational measurements with previously known data about the magnetic behavior of iron at these temperatures, the researchers found that iron’s vibrational entropy was much larger than originally suspected. In fact, the excess was similar to the entropy contribution from magnetism—suggesting that magnetism and atomic vibrations interact synergistically at moderate temperatures. This excess entropy increases the stability of the iron’s open structure even as the sample is heated past the magnetic transition.

    The technique allowed the researchers to conclude, experimentally and for the first time, that magnons—the quantum particles of electron spin (magnetism)—and phonons interact to increase iron’s stability at high temperatures.

    Because the Caltech group’s measurements matched up with the theoretical calculations that were simultaneously being developed by collaborators in the laboratory of Jörg Neugebauer at the Max-Planck-Institut für Eisenforschung GmbH (MPIE), Mauger’s results also contributed to the validation of a new computational model.

    “It has long been speculated that the structural stability of iron is strongly related to an inherent coupling between magnetism and atomic motion,” says Fritz Körmann, postdoctoral fellow at MPIE and the first author on the computational paper. “Actually finding this coupling, and that the data of our experimental colleagues and our own computational results are in such an excellent agreement, was indeed an exciting moment.”

    “Only by combining methods and expertise from various scientific fields such as quantum mechanics, statistical mechanics, and thermodynamics, and by using incredibly powerful supercomputers, it became possible to describe the complex dynamic phenomena taking place inside one of the technologically most used structural materials,” says Neugebauer. “The newly gained insight of how thermodynamic stability is realized in iron will help to make the design of new steels more systematic.”

    For thousands of years, metallurgists have been working to make stronger steels in much the same way that you’d try to develop a recipe for the world’s best cookie: guess and check. Steel begins with a base of standard ingredients—iron and carbon—much like a basic cookie batter begins with flour and butter. And just as you’d customize a cookie recipe by varying the amounts of other ingredients like spices and nuts, the properties of steel can be tuned by adding varying amounts of other elements, such as chromium and nickel.

    With a better computational model for the thermodynamics of iron at different temperatures—one that takes into account the effects of both magnetism and atomic vibrations—metallurgists will now be able to more accurately predict the thermodynamic properties of iron alloys as they alter their recipes.

    The experimental work was published in a paper titled Nonharmonic Phonons in α-Iron at High Temperatures,” in the journal Physical Review B. In addition to Fultz and first author Mauger, other Caltech coauthors include Jorge Alberto Muñoz (PhD ’13) and graduate student Sally June Tracy. The computational paper, Temperature Dependent Magnon-Phonon Coupling in bcc Fe from Theory and Experiment, was coauthored by Fultz and Mauger, led by researchers at the Max Planck Institute, and published in the journal Physical Review Letters. Fultz’s and Mauger’s work was supported by funding from the U.S. Department of Energy.

    See the full article here.

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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