|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.
Observations from NASA's Voyager spacecraft, humanity's farthest deep space sentinels, suggest the edge of our Solar System may not be smooth, but filled with a turbulent sea of magnetic bubbles. While using a new computer model to analyse Voyager data, scientists found the Sun's distant magnetic field is made up of bubbles approximately 16 billion km wide. The bubbles are created when magnetic field lines reorganise. A new model suggests that the field lines are broken up into self-contained structures disconnected from the solar magnetic field. "The Sun's magnetic field extends all the way to the edge of the Solar System," said astronomer Merav Opher of Boston University. "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, the folds of the skirt bunch up."WATCH: Voyager Finds Magnetic Foam at Solar System's Edge.
Entering the 'foam zone'.
Like Earth, our Sun has a magnetic field with a north pole and a south pole. 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 reorganise 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!" said Opher's colleague, University of Maryland physicist Jim Drake. Voyager 1 entered the ‘foam-zone’ around 2007, and Voyager 2 followed about a year later. They are more than 16 billion km away from Earth, travelling in a boundary region. In that area, the solar wind and magnetic field are affected by material expelled from other stars in our corner of the Milky Way galaxy. Understanding the structure of the Sun's magnetic field will allow scientists to explain how galactic cosmic rays enter our Solar System and help define how the star interacts with the rest of the galaxy.
More surprises ahead.
So 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 analyse with the appropriate care. Thus, unravelling the magnetic signatures of bubbles in the Voyager data is ongoing. "We are still trying to wrap our minds around the implications of the findings," said Drake, of the study published in the current issue of the Astrophysical Journal. "We'll probably discover which is correct as the Voyagers proceed deeper into the froth and learn more about its organisation," said Opher. "This is just the beginning, and I predict more surprises ahead." A good or bad thing? 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 appear to 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. Launched in 1977, the Voyager twin spacecraft have been on a 33-year journey and are en route to reach the edge of interstellar space. - Cosmos Magazine.