NASA’s two Voyager spacecraft set out from Earth back in 1977 and have been traveling towards the edge of the solar system ever since. They have now reached the heliopause, the edge of the heliosphere where the solar wind and the Sun’s magnetic field end and the interstellar magnetic field begins. Scientists had long thought that this transition was orderly, with the Sun’s magnetic field lines neatly turning back to reconnect with the Sun. But now NASA scientists are finding that this region of the solar system is far more complex.
Voyager 1 and 2, now about 9 billion miles from Earth, reached this region of odd space in 2007 and 2008, respectively, and started sending back unexpected data. It’s taken some time for scientists to realize what exactly is going on, but the Voyagers appear to be traveling through a foam-like zone of magnetic bubbles, each about 100 million miles across.
As the Sun spins, its magnetic field twists and wrinkles and, far away, bunches up in folds. Within those folds, magnetic field lines twist and cross and reconnect, forming the magnetic bubbles (watch the video below).
Scientists are particularly interested in how these bubbles interact with cosmic rays, subatomic particles that originate in outer space and are a source of radiation (we’re largely shielded here on Earth, but how to shield future space travelers is still an unanswered question). The foam might let cosmic rays pass between the bubbles, but the bubbles might trap the cosmic rays within them.