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  • richardmitnick 9:27 am on September 17, 2014 Permalink | Reply
    Tags: , , , , , , NOVA   

    From NOVA: “Chasing the Edge of the Solar System” Old But Worth a Look 

    PBS NOVA

    NOVA

    Tue, 09 Apr 2013
    David McComas

    For most of its lifetime, Voyager 1 has been traveling through uncharted territory. Initially launched to study the outer planets, Voyager 1 has soldiered on past Jupiter and Saturn and on to the outer edges of the solar system. It’s currently the farthest human-made object from Earth, but when will it be the first spacecraft to travel between the stars? Well, we won’t know until we answer two more fundamental questions: Where does our solar system end and the rest of the space between the stars begin? And if you were at the “edge” of our solar system, how would you know you had left? Recent scientific discussions on the Voyager spacecraft missions have captivated many people. And as the scientific debate swirled around the internet in near-real time, it became clear that these questions are not easy to answer. Voyager spacecraft
    The identical Voyager 1 and Voyager 2 are currently probing the farthest reaches of the solar system.

    NASA Voyager 2
    NASA/Voyager 2

    As the Principal Investigator for NASA’s Interstellar Boundary Explorer, or IBEX, spacecraft, I lead a team that is also studying this last frontier of our solar system. Data from IBEX complements the Voyager spacecraft—both missions are working together to find the very farthest reaches of the solar system. Unlike the Voyager spacecraft, which are careening out into interstellar space, IBEX orbits the Earth, collecting particles that have traveled in from the solar system’s boundary region and beyond. From those particles, we can determine many things, including what the boundary is like and what, exactly, is happening out there.

    NASA IBEX
    NASA/IBEX

    More Than Planets

    Most everyone knows our solar system is composed of small solid objects orbiting the Sun—planets, comets, and asteroids. But there’s more to it than that. Our Sun continuously emits a “wind” of material outward in all directions, typically at speeds of about a million miles per hour (1.6 million kilometers per hour). The solar wind is composed mostly of charged particles, such as electrons and protons. It also carries the Sun’s magnetic field. As the solar wind streams away from the Sun, it races out past all the planets, past Pluto, and toward the space between the stars more than 10 billion miles away. We tend to think of that space as empty, but it’s not. Rather, it contains cold hydrogen gas, dust, ionized gas, and traces of other material. Called the interstellar medium, it’s a very thin mix that comes from exploded stars and the stellar wind of other stars. When the magnetic fields of the solar wind hit the magnetic fields of the interstellar medium, they do not intermix. The expanding solar wind pushes against the interstellar medium, clearing out a cavity in interstellar space known as the heliosphere. The boundary of that bubble is where the solar wind’s strength exactly matches the pressure of the interstellar medium. We call it the heliopause, and it’s often considered to be the very outer edge of our solar system.

    The Heliopause.

    A few things about the heliopause: It isn’t an impermeable wall. Instead, it’s more like the edge of a forest clearing—the boundary is well defined, but easily negotiated. It’s also shaped more like a drop of water than a uniform sphere. That’s because our entire heliosphere, which contains our Sun, the planets, and everything else in our solar system, is moving through the interstellar medium at about 50,000 miles per hour (80,000 kilometers per hour). That motion creates a wake in the interstellar medium, much like a boat moving through water. As the solar system travels through the interstellar medium the heliopause is closest at the “front,” or the foremost point in the direction in which our solar system is traveling. At that point, the heliopause is still over 10 billion miles, or 16 billion kilometers, from the Sun.

    hh
    Heliosphere and heliopause

    As solar wind pushes out against the interestellar medium, it creates a bubble known as the heliosphere; the boundary between the two is known as the heliopause. The termination shock is where the solar wind slows as it presses against more of the interstellar medium, which also raises the plasma’s temperature. The bow wave is where the interstellar medium material piles up in front of our heliosphere, similar to water in front of a moving boat
    At least, that’s our best guess. We don’t know exactly where the boundary is or what it’s like. That’s what the IBEX and Voyager missions are trying to find out. IBEX lets us peer into the boundaries of our solar system to get a better idea of what it’s like and what’s happening there. However, because IBEX orbits the Earth, we cannot use it to mark where the boundary is located. That’s where Voyager 1 and 2 come in. Currently, they are directly sampling the boundary region. Several of the instruments on Voyager 1 and 2 are no longer working, including the cameras used to snap the stunning fly-by photos of Jupiter, Saturn, Uranus, and Neptune, but others that detect charged particles and magnetic fields are still gathering data. Both Voyagers are traveling in roughly the same direction as our solar system through the interstellar medium. We expect Voyager 1, the quicker and farther out of the two, to reach the heliopause first. Currently, it’s just over 11 billion miles, or 18 billion kilometers, from the Sun. This is so distant that radio signals from Voyager 1, which are traveling at the speed of light, take 17 hours to reach Earth.

    Three Criteria

    Before we can declare that Voyager 1 has crossed the heliopause, we are waiting to observe three main changes:

    A decrease in highly energetic charged particles from inside our heliosphere,
    An increase in highly energetic charged particles from outside our heliosphere,
    And a change in the strength and direction of the magnetic field, matching that outside the heliosphere.

    Voyager 1 observed the first two in late 2012, and IBEX has provided what are likely the best observations of the third. By using IBEX to look at particles that have traveled in from outside the heliosphere, we have an idea of the direction of the magnetic field beyond the solar system, and it’s very different from the Sun’s, which is carried out by the solar wind. So far Voyager 1 hasn’t observed this change direction of the magnetic field. That’s why we don’t think that Voyager 1 has crossed the heliopause—yet.

    The IBEX satellite orbits the Earth, capturing particles that have traveled into the solar system from beyond the heliosphere.
    Now, Voyager 1 has clearly passed into a new region of space, one that we have not detected before. Every new bit of data coming from the venerable spacecraft is teaching us more about this uncharted territory. All of this information is new, and we are learning more every day. So, do we know when Voyager 1 will cross the heliopause? We really have no idea. And that’s part of the fun. But learning about the edge of space is more than just an esoteric pursuit. Our heliosphere is a protective cocoon, a crucial layer of shielding against dangerous charged particles, known as galactic cosmic rays, that are harmful to living things. Understanding it will help us understand how the heliosphere has protected our solar system, enabling life to flourish on this planet we call home. And someday, that knowledge will help us prepare for our first voyage beyond the protective cocoon of the solar system, when we step across the threshold and venture into deep space.

    See the full article here.

    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

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  • richardmitnick 1:28 pm on August 7, 2014 Permalink | Reply
    Tags: , Bacteria, NOVA   

    From NOVA: “This Bacterium Can Survive on Electricity Alone” 

    PBS NOVA

    NOVA

    21 Jul 2014
    Allison Eck

    Scientists are hoping that a large battery in a South Dakotan gold mine could lure curious forms of bacteria that may help us understand what powers life as we know it.

    That’s because scientists have begun to discover bacteria that live and thrive on electricity alone. Rather than mediating electrons through third-party materials (such as sugar or oxygen) like most organisms do, these bacteria transmit them unaccompanied by anything else. Understanding how these interactions work could give us a glimpse of the kind of life that might exist on other planets.

    bact
    Geobacter sulfurreducens breathes by transferring electrons to iron oxides found in soil.

    Here’s Catherine Brahic, writing for New Scientist:

    Unlike any other living thing on Earth, electric bacteria use energy in its purest form—naked electricity in the shape of electrons harvested from rocks and metals. We already knew about two types, Shewanella and Geobacter. Now, biologists are showing that they can entice many more out of rocks and marine mud by tempting them with a bit of electrical juice. Experiments growing bacteria on battery electrodes demonstrate that these novel, mind-boggling forms of life are essentially eating and excreting electricity.

    And scientists have found more than just a few new examples. Annette Rowe, a doctoral student at the University of Southern California, Los Angeles, has identified up to eight specimens demonstrating this behavior. That suggests to her advisor, Kenneth Nealson, that there could be a whole slew of organisms involved in direct extraction of electrons.

    While the immediate applications are obvious—for example, better biomachines (or self-powered devices) for human use—the findings could also tell us what life’s “bare minimum” is. In other words, at what amount of energy does life begin? And is it possible to create a bacterium that, through electric means, cannot be destroyed?

    Brahic again:

    For that we need the next stage of experiments, says Yuri Gorby, a microbiologist at the Rensselaer Polytechnic Institute in Troy, New York: bacteria should be grown not on a single electrode but between two. These bacteria would effectively eat electrons from one electrode, use them as a source of energy, and discard them on to the other electrode.

    Other-worldly expeditions to mines or deep-sea caves could help us find more examples of organisms that interact with their environments this way, thereby bringing us closer to answering some of these questions.

    See the full article here.

    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

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  • richardmitnick 10:04 am on January 22, 2014 Permalink | Reply
    Tags: , , , NOVA   

    From Don Lincoln of Fermilab via PBS Nova: Journey Into the Dark Realm 

    nova

    Fermilab Don Lincoln
    Dr. Don Lincoln

    January 22, 2014

    After nearly a century of observations, astronomers have concluded that the type of matter that makes up you and me amounts to just a scant 5% of the recipe of the universe. A ghostly form of matter called dark matter is five times more common than our familiar atoms. True to its name, dark matter emits no light; we “see” it only indirectly, by measuring its gravitational pull on ordinary atoms. So how do we know it’s really there? To be sure, we need to detect dark matter directly.

    lux
    Photomultiplier tubes in the LUX dark matter experiment. Credit: Flickr/luxdarkmatter, under a creative commons license.

    Physicists have been searching for dark matter particles for decades now. Some experiments seem to have caught them while other, equally powerful experiments have failed to find any evidence for dark matter. Most recently, the ultra sensitive LUX detector, a vat of liquid xenon buried in a mile-deep underground lab, found no evidence for dark matter and ruled out earlier measurements that had reported hints of a signal. Does this mean one or more of these results is wrong? Not necessarily. There are ways for both the LUX measurement and earlier measurements to be true, but this requires that dark matter and ordinary matter interact with each other in very specific, unexpected ways. Scientists are exploring these possibilities.

    At the same time, physicists are beginning to think a bit more creatively. Until now, scientists looking for dark matter have imagined that dark matter is very simple. Specifically they imagine that there is just single type of dark matter particle: electrically neutral, experiencing only the weak and gravitational forces and with a mass 10-1000 times that of a proton. This model is popular because it is simple. On the other hand, the universe is not obliged to honor our definition of simplicity.

    Suppose someone was studying the behavior of ordinary matter using only gravity as a probe. They’d no doubt construct a simple model of matter as a particle that was something like a neutron. However, we know that our world is very complex, that the neutron is just one member of the particle zoo and that these particles can come together in all sorts of interesting ways. Scientists are beginning to wonder if maybe dark matter might be similar.

    Perhaps dark matter isn’t just one particle but a diverse realm of dark matter particles that experience forces that don’t affect ordinary matter. These dark matter particles might interact fairly strongly with each other, but only weakly with ordinary matter. With little experimental evidence to guide them, theoretical physicists are allowed to speculate fairly freely, although there are some constraints imposed by astronomical observations.

    One idea postulates a dark equivalent to electrical charge called “dark charge.” Just as ordinary electrons and positrons (antimatter electrons) can interact with each other and emit photons, it is possible that particles carrying dark charge can interact and produce dark photons.

    It is crucial to remember that dark charge, if it exists, does not interact with ordinary matter except by way of gravity and maybe the familiar weak force. A dark matter particle carrying dark charge and a familiar particle carrying electrical charge would pass by one another without so much as a “how do you do?”

    If a complicated dark sector exists, we can see it only if there is a particle that interacts with both ordinary matter and dark matter. If we could create such a messenger particle and allow it to interact with astronomical dark matter or (more likely) decay into dark matter particles, we might be able to detect it at particle accelerators like the LHC. But there’s a catch: The experimental signature would be “missing” energy in some collisions as the energy flowed into what physicists call the dark sector, the enigmatic realm of dark matter and dark energy. Given that disappearing energy is a fairly common feature of particle collisions (e.g. when neutrinos are created), it would be tricky to pin it on the creation of dark matter messenger particles. But by measuring the distribution of “missing” energy in LHC collisions and comparing it to the predictions of known physics and theoretical models of dark matter particles, it might be possible to catch a glimpse of the dark sector.

    Of course, missing energy is just one possible signature of a complicated dark sector. Another possibility invokes the principle of supersymmetry, which postulates that every known fundamental subatomic particle has a (so far undiscovered) cousin with a different quantum spin. Were the LHC to create these theoretical supersymmetric particles in a collision, they would decay into low-mass supersymmetric particles capable of interacting with the complex dark matter sector. After another cascade of decays, a dark matter particle could emit a messenger particle that “sees” both dark matter and ordinary matter and then decay in turn into a matter-antimatter particle pair that could be picked out in the collider data. Because this scenario postulates both supersymmetry and complex dark matter, it is even more of a jump into the unknown. But given that we don’t understand a lot of the universe, sometimes wild ideas are required. As Niels Bohr once quipped to Wolfgang Pauli, “We are all agreed that your theory is crazy. The question which divides us is whether it is crazy enough.”

    So far, physicists have not found evidence for a complex dark sector, but the search has just begun. Ordinary matter is complex, so it seems very reasonable that the dark sector should be, too. Over the next several years, theorists will begin to flesh out a myriad of dark possibilities, including possibly even dark atoms, just in time for the LHC to turn back on and see if the data supports these interesting ideas.

    See the full article here.

    Don Lincoln is a senior experimental particle physicist at Fermi National Accelerator Laboratory and an adjunct professor at the University of Notre Dame. He splits his research time between Fermilab and the CERN laboratory, just outside Geneva, Switzerland. He has coauthored more than 500 scientific papers on subjects from microscopic black holes and extra dimensions to the elusive Higgs boson. When Don isn’t doing physics research, he spends his time sharing the fantastic world of science with anyone who will listen. He has given public lectures on three continents and has authored many magazine articles, YouTube videos and columns in the online periodical Fermilab Today. His book “The Quantum Frontier” tells the tale of the Large Hadron Collider, the world’s preeminent particle accelerator, while his other book “Understanding the Universe” introduces the armchair scientist to particle physics and cosmology and tells how the two fields are intertwined.

    Fermilab Logo

    Fermilab Wilson Hall
    Wilson Hall at Fermilab


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  • richardmitnick 4:51 pm on January 10, 2014 Permalink | Reply
    Tags: , , , , , NOVA   

    Kepler from NOVA 

    Great video. Don’t miss it.

    I know that Kepler’s most useful days are gone. but this is a great telling of the story.

     
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