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The barrier at the edge of our Solar System may not be the smooth shield that scientists once thought. The venerable Voyager spacecraft have detected a huge, turbulent sea of magnetic bubbles in the heliosheath — the interface between the heliosphere and interstellar space — similar to an actively bubbling Jacuzzi tub. At a briefing today, scientists said the finding is significant as “we now will have to change our view of how the Sun interacts with the Solar System,” said Arik Posner, Voyager program scientist at NASA Headquarters. But it also means that the “force field” that surrounds the entire Solar System may be letting in more harmful cosmic rays and energetic particles than previously thought.
Over 30 years into their mission, the Voyagers are still monitoring their environment and sending back data. In 2007, scientists noticed that Voyager 1 recorded dramatic dips and rises in the amount of electrons it encountered as it traveled through the heliosphere, the barrier that surrounds the entire Solar System and is created by the Sun’s magnetic field. Voyager 2 made similar observations of these charged particles in 2008.
Using a new computer model to analyze the data, scientists found the Sun’s distant magnetic field is likely made up of bubbles approximately 100 million miles (160 million kilometers) wide — “like long sausages,” said Merav Opher at the briefing, an astronomer at Boston University who is the lead author of a paper published in the Astrophysical Journal.
And the bubbles are moving around, with oscillations of plus or minus 10 to 20 km. “It is very bubbly as far as we can tell,” Jim Drake from the University of Maryland said at the press conference. “The entire thing is bubbly, like where the jets come out from a Jacuzzi.”
Opher said the bubbles, while not visible from Earth, cover a large portion of the sky at about 38 degrees latitude and as the solar winds “bumps” up against the heliopause, the bubbles fill up the entire region next to the heliopause.
Like Earth, our Sun has a magnetic field with a north pole and a south pole. The field lines are stretched outward, and as the sun rotates, the solar wind twists them into a spiral as they are carried outward.
The bubbles are created when magnetic field lines reorganize. The new model suggests the field lines are broken up into self-contained structures disconnected from the solar magnetic field.
These magnetic bubbles should act as electron traps, so the spacecraft would experience higher than normal electron bombardment as they traveled through the bubbles.
But the implications of this new finding, said Opher, is also that the heliosheath is very different from what scientists expected. She prefaced by saying that any earlier ideas about the region was only conjecture since no spacecraft has been there before. “We thought heliopause would be a smooth surface and shield us from intergalactic cosmic rays,” she said. “It is not a shield but more like a membrane that is a sea of bubbles.”
One argument would say the bubbles would seem to be a very porous shield, allowing lots of cosmic rays through the gaps. But another view would be that cosmic rays could get trapped inside the bubbles, making the bubbling froth a very good shield indeed.
However, the scientists are still working on figuring out exactly what these bubbles are. The Voyagers’ instruments, while still working fine, are being tested in this new region of space. “The magnetic instruments on Voyager were designed to measure magnetic fields, but they are right at very edge of what the instruments are capable of sensing,” said Drake. “The magnetic field is very weak. While trying to find out what these magnetic bubbles are, we haven’t reached that moment where we say, ‘yes, that is it.’ We’d like to be able to pin it down much better.”
This video from NASA’s Goddard Spaceflight Center helps to visually explain the new findings:
Sources: NASA press conference, NASA’s Sun/Earth briefing materials, press release, more videos and visuals can be found at this Goddard webpage