You would never know it from Earth, but the entire Solar System is encapsulated in a massive magnetic field produced by the sun. The border between that magnetic field and interstellar space is called the heliopause. Astrophysicists used to think it was a smooth, discrete barrier: one moment you’re in the Solar System, and after breaking through it, you’re outside and subject to interstellar wind and radiation. Now, thanks to data collected from Voyager 1 and Voyager 2, both of which have recently passed through this zone, we know it’s not a simple barrier at all – it’s actually full of magnetic “bubbles,” millions of miles wide.
The same way the Earth’s magnetic field protects us from most of the cosmic rays and radiation from the sun, the Sun’s magnetic field keeps much of the dust, debris, and radiation out of the Solar System. The Voyager probes are the first man-made objects to pass through the heliopause, and scientists were braced to see the two tiny space probes to pass through and immediately begin picking up massive amounts of radiation from the interstellar wind. That’s not quite what happened.
Instead, the two probes passed through multiple magnetic barriers, some of which were millions of miles wide. NASA scientists would see the amount of radiation spike for a while, and then vanish again, and then spike, and vanish, over and over until it finally spiked and stayed put for several years. The two Voyager 1 and Voyager 2 actually passed through the zone in 2007 and 2008, respectively, and both probes experienced the same phenomenon. The events completely puzzled NASA scientists, who could only interpret the activity as the probes moving out of a strong magnetic field, and then back in, and then back out again.
Ultimately, they came up with a new theory: that the heliopause is not a discrete barrier at all, but is instead made up of a heliosheath, or “foam zone,” made up of smaller magnetic “bubbles” that border the edge of the Solar System. To figure out why they exist, you have to remember that the Sun itself is traveling through interstellar space, orbiting the center of the galaxy once every 200 million years, itself careening through space.
As the sun moves, the magnetic field cuts through the interstellar wind like a boat through water. Just like a boat through water, there are waves and breaks along the front. They theorize that the bubbles are caused by turbulence and disruptions on the surface of the Sun’s magnetic field. The sun is also rotating and moving inside of that field, and as the sun moves and spins, the magnetic field moves and spins with it, adding to the turbulence.
In the end, this means that the border between our Solar System and deep space is actually a very violent and turbulent zone to pass through. It doesn’t mean much for physical objects, direct light, or even massive energy pulses like those emitted by gamma-ray bursts, but it does represent a complete shift in the way we thought the sun behaves with the space around it. Astrophysicists now turn to the question of what the heliosheath is for, and whether it, like the heliopause, serves to keep interstellar wind out of the Solar System, where it would irradiate all of the planets inside. Considering how long it took the Voyager probes to get through the heliosheath, it’ll be a while before we know for sure.
Read more at NASA