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  • richardmitnick 2:32 pm on April 14, 2015 Permalink | Reply
    Tags: , , , NASA   

    From NASA: “NASA’s New Horizons Spacecraft Nears Historic July 14 Encounter with Pluto” 

    NASA

    NASA

    April 14, 2015

    Dwayne Brown
    Headquarters, Washington
    202-358-1726
    dwayne.c.brown@nasa.gov

    Michael Buckley
    Johns Hopkins University Applied Physics Laboratory, Laurel, Md.
    240-228-7536
    michael.buckley@jhuapl.edu

    Maria Stothoff
    Southwest Research Institute, San Antonio
    210-522-3305
    maria.stothoff@swri.org

    NASA New Horizons spacecraft
    New Horizons

    NASA’s New Horizons spacecraft is three months from returning to humanity the first-ever close up images and scientific observations of distant Pluto and its system of large and small moons.

    2
    Pluto

    “Scientific literature is filled with papers on the characteristics of Pluto and its moons from ground based and Earth orbiting space observations, but we’ve never studied Pluto up close and personal,” said John Grunsfeld, astronaut, and associate administrator of the NASA Science Mission Directorate at the agency’s Headquarters in Washington. “In an unprecedented flyby this July, our knowledge of what the Pluto systems is really like will expand exponentially and I have no doubt there will be exciting discoveries.”

    The fastest spacecraft ever launched, New Horizons has traveled a longer time and farther away – more than nine years and three billion miles – than any space mission in history to reach its primary target. Its flyby of Pluto and its system of at least five moons on July 14 will complete the initial reconnaissance of the classical solar system. This mission also opens the door to an entirely new “third” zone of mysterious small planets and planetary building blocks in the Kuiper Belt, a large area with numerous objects beyond Neptune’s orbit.

    3
    Known objects in the Kuiper belt beyond the orbit of Neptune (scale in AU; epoch as of January 2015).

    The flyby caps a five-decade-long era of reconnaissance that began with Venus and Mars in the early 1960s, and continued through first looks at Mercury, Jupiter and Saturn in the 1970s and Uranus and Neptune in the 1980s.

    Reaching this third zone of our solar system – beyond the inner, rocky planets and outer gas giants – has been a space science priority for years. In the early 2000s the National Academy of Sciences ranked the exploration of the Kuiper Belt – and particularly Pluto and its largest moon, Charon – as its top priority planetary mission for the coming decade.

    New Horizons – a compact, lightweight, powerfully equipped probe packing the most advanced suite of cameras and spectrometers ever sent on a first reconnaissance mission – is NASA’s answer to that call.

    “This is pure exploration; we’re going to turn points of light into a planet and a system of moons before your eyes!” said Alan Stern, New Horizons principal investigator from Southwest Research Institute (SwRI) in Boulder, Colorado. “New Horizons is flying to Pluto – the biggest, brightest and most complex of the dwarf planets in the Kuiper Belt. This 21st century encounter is going to be an exploration bonanza unparalleled in anticipation since the storied missions of Voyager in the 1980s.”

    NASA Voyager 1
    Voyager 1

    Pluto, the largest known body in the Kuiper Belt, offers a nitrogen atmosphere, complex seasons, distinct surface markings, an ice-rock interior that may harbor an ocean, and at least five moons. Among these moons, the largest – Charon – may itself sport an atmosphere or an interior ocean, and possibly even evidence of recent surface activity.

    4
    Charon

    “There’s no doubt, Charon is a rising star in terms of scientific interest, and we can’t wait to reveal it in detail in July,” said Leslie Young, deputy project scientist at SwRI.

    Pluto’s smaller moons also are likely to present scientific opportunities. When New Horizons was started in 2001, it was a mission to just Pluto and Charon, before the four smaller moons were discovered.

    The spacecraft’s suite of seven science instruments – which includes cameras, spectrometers, and plasma and dust detectors – will map the geology of Pluto and Charon and map their surface compositions and temperatures; examine Pluto’s atmosphere, and search for an atmosphere around Charon; study Pluto’s smaller satellites; and look for rings and additional satellites around Pluto.

    Currently, even with New Horizons closer to Pluto than the Earth is to the Sun, the Pluto system resembles little more than bright dots in the distance. But teams operating the spacecraft are using these views to refine their knowledge of Pluto’s location, and skillfully navigate New Horizons toward a precise target point 7,750 miles (12,500 kilometers) from Pluto’s surface. That targeting is critical, since the computer commands that will orient the spacecraft and point its science instruments are based on knowing the exact time and location that New Horizons passes Pluto.

    “Our team has worked hard to get to this point, and we know we have just one shot to make this work,” said Alice Bowman, New Horizons mission operations manager at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, which built and operates the spacecraft. “We’ve plotted out each step of the Pluto encounter, practiced it over and over, and we’re excited the ‘real deal’ is finally here.”

    The spacecraft’s work doesn’t end with the July flyby. Because it gets one shot at its target, New Horizons is designed to gather as much data as it can, as quickly as it can, taking about 100 times as much data on close approach as it can send home before flying away. And although the spacecraft will send select, high-priority datasets home in the days just before and after close approach, the mission will continue returning the data stored in onboard memory for a full 16 months.

    “New Horizons is one of the great explorations of our time,” said New Horizons Project Scientist Hal Weaver at APL. “There’s so much we don’t know, not just about Pluto, but other worlds like it. We’re not rewriting textbooks with this historic mission – we’ll be writing them from scratch.”

    APL manages the New Horizons mission for NASA’s Science Mission Directorate in Washington. Alan Stern of SwRI is the principal investigator. SwRI leads the science team, payload operations and encounter science planning. New Horizons is part of the New Frontiers Program, managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama.

    For more information on New Horizons, visit:

    http://www.nasa.gov/newhorizons

    and

    http://pluto.jhuapl.edu

    See the full article here.

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    The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.

    President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

    Since that time, most U.S. space exploration efforts have been led by NASA, including the Apollo moon-landing missions, the Skylab space station, and later the Space Shuttle. Currently, NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle and Commercial Crew vehicles. The agency is also responsible for the Launch Services Program (LSP) which provides oversight of launch operations and countdown management for unmanned NASA launches. Most recently, NASA announced a new Space Launch System that it said would take the agency’s astronauts farther into space than ever before and lay the cornerstone for future human space exploration efforts by the U.S.

    NASA science is focused on better understanding Earth through the Earth Observing System, advancing heliophysics through the efforts of the Science Mission Directorate’s Heliophysics Research Program, exploring bodies throughout the Solar System with advanced robotic missions such as New Horizons, and researching astrophysics topics, such as the Big Bang, through the Great Observatories [Hubble, Chandra, Spitzer, and associated programs. NASA shares data with various national and international organizations such as from the [JAXA]Greenhouse Gases Observing Satellite.

     
  • richardmitnick 8:03 pm on February 4, 2015 Permalink | Reply
    Tags: , , , NASA   

    From WIRED: “The White House Wants to Go to Europa” 

    Wired logo

    Wired

    02.04.15
    Marcus Woo

    1
    The blue and white areas on Europa’s surface are close to pure water ice. NASA/JPL-Caltech/SETI Institute

    Earlier this week the White House made public its budget requests for 2016. It’s a little bit of Washington kabuki—Congress always adjusts the budget one way or the other. But buried inside the $18.5 billion budget request for NASA was an interesting tidbit: $30 million for a mission to the Jovian moon Europa, every space nerd’s favorite target in the search for extraterrestrial life.

    In other words, if this new funding goes through, it’ll mean that NASA is finally, officially onboard with a mission to the ice-crusted world where alien monoliths took over in Arthur C. Clarke’s 2010. In other other words: Let’s go to Europa! “This is a big deal,” says Casey Dreier, the director of advocacy at the Planetary Society, which has been lobbying for this mission for more than 15 years. “This budget basically fills in the missing piece that will enable this mission to go forward.” The new budget request also says that the White House plans to ask for even more money in the next few years, and because the mission is now an official project, says Dreier, civil servants can work on it and NASA can start making long-term contracts for further planning.

    So what would the mission look like? Europa’s icy shell gives it the smoothest surface of any world in the solar system. But shifting cracks and other evidence suggest that that below that frozen surface lies an ocean—a watery one. And where there’s water, life may follow. Researchers have wanted to get there for decades—the current best idea for how is a 15-year-old concept called the Europa Clipper. “What we’ve been looking at is a multiple flyby mission,” says Bob Pappalardo, the mission’s project scientist. Under the current plan, a spacecraft will orbit Jupiter, not Europa—but it’ll zip past the moon 45 times in three years—venturing as close as 16 miles to the surface every couple of weeks.

    Scientists are still hashing out what kinds of instruments will be onboard, so Pappalardo can’t say which exact ones will end up going to Europa. But one of the main goals will be to measure the moon’s magnetic field, which would tell scientists how salty the subsurface ocean is. Dissolved minerals (like salt) allow the ocean to conduct electricity—which means it’d have a magnetic field a sensor could read. Or more speculatively, in 2013 the Hubble Space Telescope spotted what looked like 125-mile high geysers spewing water from Europa’s south pole. Maybe a probe could actually fly through one and sample the water. Radar could reveal how thick the frozen crust is, and other instruments could measure the chemicals in Europa’s wispy atmosphere. High-resolution cameras will take pictures of the cracks that crisscross the surface, hoping to figure out whether it’s actually the case that the ice flexes and breaks because of that still-hypothetical ocean. And they’ll also scope out possible spots to send a future lander.

    That’s the real brass ring, of course—if you want to find aliens. “If someone comes up with a clever way to point to life with multiple flybys, that will be wonderful,” Pappalardo says. “But that will probably take going to the surface.” That’s why Earthbound experiments like the work at Lake Vostok in Antarctica are so interesting to planetary scientists—cracking through 2.5 miles of ice to get to a liquid lake below without contaminating it may turn out to be highly relevant expertise someday.

    When that’ll happen, though, is another question. The price tag for something Europa Clipper-like looks to be about $2 billion, so it’ll take a few more years of budgets to get it all together. A mission with a lander would be much more expensive. An orbiter might still be a possibility, but “it’s a riskier and more expensive approach than making many flybys,” Pappalardo says. It would take a year and a half after arriving at Jupiter just to get into Europa’s orbit, requiring lots more fuel and exposing the spacecraft to radiation that could fry its instruments.

    However the details turn out, a Europa mission could launch as soon as the mid-2020s, said David Radzanowski, NASA’s chief financial officer, in a press briefing on Monday. Which means it won’t actually get to Europa until around 2030. But if all goes as planned, those 15 years will fly right by.

    See the full article here.

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  • richardmitnick 4:39 pm on January 23, 2015 Permalink | Reply
    Tags: , , NASA, U Montana   

    From SPACE.com: “How Did Life Become Complex, and Could It Happen Beyond Earth?” 

    space-dot-com logo

    SPACE.com

    January 20, 2015
    Elizabeth Howell, Astrobiology Magazine

    When astrobiologists contemplate life on nearby planets or moons, they often suggest such life would be simple. Instead of there being some kind of multicellular organism on, say, Jupiter’s moon Europa, scientists instead aim to find something more like a microbe.

    But from such simple life, more complex lifeforms could eventually come to be. That’s what happened here on planet Earth, and that’s what could happen in other locations as well. How did the chemistry evolve to get life to where we are today? What transitions took place?

    1
    Studying areas such as Titan, a moon of Saturn (foreground) can give researchers ideas about how chemistry eventually created life.
    Credit: NASA/JPL-Caltech/Space Science Institute

    Frank Rosenzweig, an evolutionary geneticist at the University of Montana, is looking into such questions over the next five years with funding from the NASA Astrobiology Institute. His lab studies how life evolves “complex traits,” factors that influence everything from lifespan to biodiversity.

    “Over my career, I’ve been interested in what are the genetic bases of adaptation and how do complex communities evolve from single clones,” Rosenzweig said. “Related to these questions are others such as how do the genetic ‘starting point’ and ecological setting influence the tempo and trajectory of evolutionary change.”

    Shopping for life in the Solar System

    Complex life is only known to exist on Earth, but scientists aren’t ruling out other locations in the Solar System. Our understanding of life’s evolution could be informed by studying the Saturnian moon Titan, whose hydrocarbon chemistry is considered a precursor to a living system. Researchers recently tried to replicate a substance in Titan’s atmosphere called tholins, which are organic aerosols created from solar radiation hitting the methane and nitrogen atmosphere.

    2
    Tholins, complex organic molecules fundamental to prebiotic chemistry, are apparently forming at a much higher altitude, and in different ways than expected, in Titan’s atmosphere.

    Understanding how tholins and other substances are formed on Titan could give researchers a picture of how early Earth evolved life. Also, studying how Earthly life-forms and their biochemical precursors evolved from simple subunits to successively more complex and interdependent systems could give hints of how life might evolve on other moons or planets.

    On Earth, examples of these transitions include collections of single proteins evolving into protein networks. For example, single-celled bacteria evolve into eukaryotic cells that contain two, or even three genomes. Also, competing microbes come together to form cooperative systems, such as microbial mats in hot springs and microbial biofilms lining the human gut. Each of these transitions results in increased bio-complexity, interdependence and a certain degree of autonomy for a new whole that is more than the sum of its parts.

    Rosenzweig’s research developed out of previous NASA grants over the past six years, and from his being a panelist reviewing team-based proposals for the NASA Astrobiology Institute.

    “There is, and still needs to be a lot of work done on chemical evolution, prebiotic (pre-life) evolution, extreme environments and bio-signatures,”Rosenzweig said. “It struck me that it might be worthwhile trying to convince NASA to add to its research portfolio a set of proposals focused on understanding the genetic basis underlying major evolutionary transitions that have led to higher-order complexity”

    As such, Rosenzweig’s new research will focus on four areas where a complex system has arisen from simpler elements: metabolism, the eukaryotic cell, mutualism (co-operating species) and multicellularity. He will also look into a fifth area — mutations and gene interactions — that critically determines how quickly such complex systems can arise. He believes that lab experiments aimed at replicating key aspects of the evolution of life on Earth can better inform how we search in life-friendly locations on Mars, Europa, Saturn’s moon Titan, or elsewhere.

    Rosenzweig plans to have eight different teams focusing on questions of evolution and changes from simple to more complex life. To integrate his teams’ experimental results into a broader framework he recruited theoreticians in the areas of population genetics and statistical physics.

    Rosenzweig’s previous NASA funding came from the Exobiology and Evolutionary Biology Program. The first project, initiated in 2007, examined how genetic material (or genomes) evolve in yeast species that were cultured under limited resources. A second project, initiated in 2010, is investigating how founder cells in E. coli genotypes, and the environment in which they evolve, influence the diversity and stability of subsequent populations.

    3
    A species of yeast (Saccharomyces cerevisiae) seen in a scanning electrograph image.
    Credit: NASA

    The first project led to an unexpected finding: stress may increase the frequency with which genome sequences are rearranged. Stress introduces new chromosomal variants into the species; population that could prove beneficial under challenging circumstances. Indeed, previous studies have indicated that new chromosomal variants are stress resistant. In 2013, Rosenzweig’s team, led by University of Montana research professor Eugene Kroll, began studying how yeast cultures respond to starvation.

    This new line of inquiry has already led to one major publication entitled, Starvation-associated genome restructuring can lead to reproductive isolation in yeast, which was published in PLoS One in 2013. Therein, Kroll and Rosenzweig further show that yeast containing stress-adaptive genomic rearrangements become “reproductively isolated” from their ancestors, suggesting that, at least in lower fungi, geographic isolation may not be required to generate new species. A new project through NASA’s Exobiology and Evolutionary Biology Program, awarded Summer 2014, will enable the team to tease out the genetic mechanisms that underlie adaptation and reproductive isolation in starved yeast.

    A distinguishing feature of this research, Rosenzweig notes, is that whereas most studies look at species’ performance in relatively benign environments, the yeast are studied under near-starvation conditions. This kind of severe stress may be a closer analog to what real species face in nature as populations genetically adapt to drastically altered circumstances. Inasmuch as starvation may serve as a cue to any kind of stress, from diminished resources to greatly altered temperature to an invasion by superior competitors, the results of this study should have implications for life on other planets.

    5
    Studying how life evolved on Earth could lead to a better understanding of habitability conditions in other locations, such as Mars.
    Credit: NASA/JPL

    Indeed, a major theme that runs through all of these investigations is that by studying evolutionary processes in the laboratory using simple unicellular species, we can expect to uncover rules that govern the tempo and trajectory of evolution in any population of self-replicating entities whose structure and function are programmed by information molecules.

    “What I would like fellow astrobiology researchers to be alert to is evidence of differentiation, either at the level of different proteins in a metabolic network, different genotypes in a population of a given species, different genomes in a single cell, or different cells in a multicellular organism. In each case differentiation opens the door not only to competition but also to cooperation between variants, enabling a division of labor.” he said. “We should be mindful that, however they may be encoded, lifeforms are likely to have differentiated on other worlds. Therefore, we should be alert to the signatures left by these more complex forms of life.”

    See the full article here.

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  • richardmitnick 2:42 pm on April 16, 2014 Permalink | Reply
    Tags: , , , NASA,   

    From M.I.T.: “A river of plasma, guarding against the sun” 

    March 6, 2014
    Jennifer Chu, MIT News Office

    MIT scientists identify a plasma plume that naturally protects the Earth against solar storms.

    The Earth’s magnetic field, or magnetosphere, stretches from the planet’s core out into space, where it meets the solar wind, a stream of charged particles emitted by the sun. For the most part, the magnetosphere acts as a shield to protect the Earth from this high-energy solar activity.

    But when this field comes into contact with the sun’s magnetic field — a process called “magnetic reconnection” — powerful electrical currents from the sun can stream into Earth’s atmosphere, whipping up geomagnetic storms and space weather phenomena that can affect high-altitude aircraft, as well as astronauts on the International Space Station.

    magrec
    Magnetic Reconnection: This view is a cross-section through four magnetic domains undergoing separator reconnection. Two separatrices divide space into four magnetic domains with a separator at the center of the figure. Field lines (and associated plasma) flow inward from above and below the separator, reconnect, and spring outward horizontally. A current sheet (as shown) may be present but is not required for reconnection to occur. This process is not well understood: once started, it proceeds many orders of magnitude faster than predicted by standard models.

    Now scientists at MIT and NASA have identified a process in the Earth’s magnetosphere that reinforces its shielding effect, keeping incoming solar energy at bay.

    sun

    By combining observations from the ground and in space, the team observed a plume of low-energy plasma particles that essentially hitches a ride along magnetic field lines — streaming from Earth’s lower atmosphere up to the point, tens of thousands of kilometers above the surface, where the planet’s magnetic field connects with that of the sun. In this region, which the scientists call the merging point, the presence of cold, dense plasma slows magnetic reconnection, blunting the sun’s effects on Earth.

    “The Earth’s magnetic field protects life on the surface from the full impact of these solar outbursts,” says John Foster, associate director of MIT’s Haystack Observatory. “Reconnection strips away some of our magnetic shield and lets energy leak in, giving us large, violent storms. These plasmas get pulled into space and slow down the reconnection process, so the impact of the sun on the Earth is less violent.”

    Foster and his colleagues publish their results in this week’s issue of Science. The team includes Philip Erickson, principal research scientist at Haystack Observatory, as well as Brian Walsh and David Sibeck at NASA’s Goddard Space Flight Center.

    Mapping Earth’s magnetic shield

    For more than a decade, scientists at Haystack Observatory have studied plasma plume phenomena using a ground-based technique called GPS-TEC, in which scientists analyze radio signals transmitted from GPS satellites to more than 1,000 receivers on the ground. Large space-weather events, such as geomagnetic storms, can alter the incoming radio waves — a distortion that scientists can use to determine the concentration of plasma particles in the upper atmosphere. Using this data, they can produce two-dimensional global maps of atmospheric phenomena, such as plasma plumes.

    These ground-based observations have helped shed light on key characteristics of these plumes, such as how often they occur, and what makes some plumes stronger than others. But as Foster notes, this two-dimensional mapping technique gives an estimate only of what space weather might look like in the low-altitude regions of the magnetosphere. To get a more precise, three-dimensional picture of the entire magnetosphere would require observations directly from space.

    Toward this end, Foster approached Walsh with data showing a plasma plume emanating from the Earth’s surface, and extending up into the lower layers of the magnetosphere, during a moderate solar storm in January 2013. Walsh checked the date against the orbital trajectories of three spacecraft that have been circling the Earth to study auroras in the atmosphere.

    As it turns out, all three spacecraft crossed the point in the magnetosphere at which Foster had detected a plasma plume from the ground. The team analyzed data from each spacecraft, and found that the same cold, dense plasma plume stretched all the way up to where the solar storm made contact with Earth’s magnetic field.

    A river of plasma

    Foster says the observations from space validate measurements from the ground. What’s more, the combination of space- and ground-based data give a highly detailed picture of a natural defensive mechanism in the Earth’s magnetosphere.

    “This higher-density, cold plasma changes about every plasma physics process it comes in contact with,” Foster says. “It slows down reconnection, and it can contribute to the generation of waves that, in turn, accelerate particles in other parts of the magnetosphere. So it’s a recirculation process, and really fascinating.”

    Foster likens this plume phenomenon to a “river of particles,” and says it is not unlike the Gulf Stream, a powerful ocean current that influences the temperature and other properties of surrounding waters. On an atmospheric scale, he says, plasma particles can behave in a similar way, redistributing throughout the atmosphere to form plumes that “flow through a huge circulation system, with a lot of different consequences.”

    “What these types of studies are showing is just how dynamic this entire system is,” Foster adds.

    Tony Mannucci, supervisor of the Ionospheric and Atmospheric Remote Sensing Group at NASA’s Jet Propulsion Laboratory, says that although others have observed magnetic reconnection, they have not looked at data closer to Earth to understand this connection.

    “I believe this group was very creative and ingenious to use these methods to infer how plasma plumes affect magnetic reconnection,” says Mannucci, who was not involved in the research. “This discovery of the direct connection between a plasma plume and the magnetic shield surrounding Earth means that a new set of ground-based observations can be used to infer what is occurring deep in space, allowing us to understand and possibly forecast the implications of solar storms.”

    See the full article here.


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  • richardmitnick 6:44 pm on February 21, 2013 Permalink | Reply
    Tags: , , , , , , NASA,   

    From NASA Chandra: “Chemistry and the Universe” 

    NASA Chandra

    Chemistry, the study of the intricate dances and bondings of low-energy electrons to form the molecules that make up the world we live in, may seem far removed from the thermonuclear heat in the interiors of stars and the awesome power of supernovas. Yet, there is a fundamental connection between them.

    To illustrate this connection, the familiar periodic table of elements—found in virtually every chemistry class—has been adapted to show how astronomers see the chemical Universe. What leaps out of this table is that the simplest elements, hydrogen and helium, are far and away the most abundant.

    pt
    Periodic Table alteration

    PeriodicTable2
    The Periodic Table

    The Universe started out with baryonic matter in its simplest form, hydrogen. In just the first 20 minutes or so after the Big Bang, about 25% of the hydrogen was converted to helium. In essence, the chemical history of the Universe can be divided into two mainphases: one lasting 20 minutes, and the rest lasting for 13.7 billion years and counting.

    One of the principal scientific accomplishments of the Chandra X-ray Observatory has been to help unravel how the chemical enrichment by stellar winds and supernovas works on a galactic and intergalactic scale.

    super
    Cassiopeia A (Cas A, for short), the youngest supernova remnant in the Milky Way.Credit: NASA/CXC/MIT/UMass Amherst/M.D.Stage et al.

    Chandra images and spectra of individual supernova remnants reveal clouds of gas rich in elements such as oxygen, silicon, sulfur, calcium and iron, and track the speed at which these elements have been ejected in the explosion. The Chandra image of the Cas A supernova remnant shows iron rich ejecta outside silicon-rich ejecta, thus indicating that turbulent mixing and an aspherical explosion turned much of the original star inside out. Observations of Doppler-shifted emission lines for Cas A and other supernova remnants are providing three-dimensional information on the distribution and velocity of the supernova ejecta which will help to constrain models for the explosion.

    dstar mass

    See the full article here.

    Chandra X-ray Center, Operated for NASA by the Smithsonian Astrophysical Observatory
    Smithsonian Astrophysical Observatory


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