A Big Surprise from the Edge of the Solar System   
       
   June 9, 2011: NASA's Voyager probes are truly going where no one has gone   
   before. Gliding silently toward the stars, 9 billion miles from Earth, they   
   are beaming back news from the most distant, unexplored reaches of the solar   
   system.   
       
   Mission scientists say the probes have just sent back some very big news   
   indeed.   
       
   It's bubbly out there.   
       
   "The Voyager probes appear to have entered a strange realm of frothy magnetic   
   bubbles," says astronomer Merav Opher of Boston University. "This is very    
   urprising."   
   [...]   
   A NASA video shows how magnetic bubbles might be formed at the edge of the   
   solar system.   
       
   According to computer models, the bubbles are large, about 100 million miles   
   wide, so it would take the speedy probes weeks to cross just one of them.   
   Voyager 1 entered the "foam-zone" around 2007, and Voyager 2 followed about a   
   year later. At first researchers didn't understand what the Voyagers were   
   sensing--but now they have a good idea.   
       
   "The sun's magnetic field extends all the way to the edge of the solar   
   system," explains Opher. "Because the sun spins, its magnetic field becomes   
   twisted and wrinkled, a bit like a ballerina's skirt. Far, far away from the   
   sun, where the Voyagers are now, the folds of the skirt bunch up."   
   [...]   
   Magnetic bubbles at the edge of the solar system are about 100 million miles   
   wide--similar to the distance between Earth and the sun. [more]   
       
   When a magnetic field gets severely folded like this, interesting things can   
   happen. Lines of magnetic force criss-cross and "reconnect". (Magnetic   
   reconnection is the same energetic process underlying solar flares.) The   
   crowded folds of the skirt reorganize themselves, sometimes explosively, into   
   foamy magnetic bubbles.   
       
   "We never expected to find such a foam at the edge of the solar system, but   
   there it is!" says Opher's colleague, University of Maryland physicist Jim   
   Drake.   
       
   Theories dating back to the 1950s had predicted a very different scenario: The   
   distant magnetic field of the sun was supposed to curve around in relatively   
   graceful arcs, eventually folding back to rejoin the sun. The actual bubbles   
   appear to be self-contained and substantially disconnected from the broader   
   solar magnetic field.   
       
   Energetic particle sensor readings suggest that the Voyagers are occasionally   
   dipping in and out of the foam-so there might be regions where the old ideas   
   still hold. But there is no question that old models alone cannot explain what   
   the Voyagers have found.   
       
   Says Drake: "We are still trying to wrap our minds around the implications of   
   these findings."   
       
   The structure of the sun's distant magnetic field-foam vs. no-foam-is of acute   
   scientific importance because it defines how we interact with the rest of the   
   galaxy. Researchers call the region where the Voyagers are now "the   
   heliosheath." It is essentially the border crossing between the Solar System   
   and the rest of the Milky Way. Lots of things try to get across-interstellar   
   clouds, knots of galactic magnetism, cosmic rays and so on. Will these   
   intruders encounter a riot of bubbly magnetism (the new view) or graceful   
   lines of magnetic force leading back to the sun (the old view)?   
   [...]   
   Old and new views of the heliosheath. Red and blue spirals are the gracefully   
   curving magnetic field lines of orthodox models. New data from Voyager add a   
   magnetic froth (inset) to the mix. Larger images: old, new.   
       
   The case of cosmic rays is illustrative. Galactic cosmic rays are subatomic   
   particles accelerated to near-light speed by distant black holes and supernova   
   explosions. When these microscopic cannonballs try to enter the solar system,   
   they have to fight through the sun's magnetic field to reach the inner planets.   
       
   "The magnetic bubbles could be our first line of defense against cosmic rays,"   
   points out Opher. "We haven't figured out yet if this is a good thing or not."   
       
   On one hand, the bubbles would seem to be a very porous shield, allowing many   
   cosmic rays through the gaps. On the other hand, cosmic rays could get trapped   
   inside the bubbles, which would make the froth a very good shield indeed.   
       
   "We'll probably discover which is correct as the Voyagers proceed deeper into   
   the froth and learn more about its organization1," says Opher. "This is just   
   the beginning, and I predict more surprises ahead."   
       
       
   Author: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   Footnote:1So far, much of the evidence for the bubbles comes from the Voyager   
   energetic particle and flow measurements. Proof can also be obtained from the   
   Voyager magnetic field observations and some of this data is also very   
   suggestive. However, because the magnetic field is so weak, the data takes   
   much longer to analyze with the appropriate care. Thus, unraveling the   
   magnetic signatures of bubbles in the Voyager data is ongoing.   
       
   Voyager Interstellar Mission -- home page   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.62   
    * Origin: NCS BBS (1:3828/7)