When NASA launched its Voyager 1 and 2 spacecraft 33 years ago, the probes' primary mission was to explore Jupiter and Saturn. But the two satellites have performed above and beyond their original duty: As of March 2012, Voyager 2 was 14.7 billion kilometers away from Earth, in the heliosheath—the outermost layer of the heliosphere where the solar wind is slowed by the pressure of interstellar gas—and yesterday, at the American Geophysical Union meeting in San Francisco, scientists reported that Voyager 2 has entered a new region at the edge of our solar system, which they believe is the final area the spacecraft has to cross before hitting interstellar space: a magnetic highway for charged particles.
Scientists call this region a magnetic highway because of the connection between our sun's magnetic field lines and interstellar magnetic field lines, which allows lower-energy charged particles from our heliosphere to zoom out into interstellar space, and higher-energy particles from outside to come in. Before Voyager 1 entered this region for the first time on July 28, the charged particles bounced in all directions, "as if trapped on local roads inside the heliosphere," according to a NASA press release. The region ebbed and flowed toward Voyager 1 several times before the craft entered it again on August 25; the environment has since been stable. The magnetic highway is still inside our solar system, scientist believe, the because the direction of the magnetic field lines haven't changed. (The Voyager probes are sending data back to NASA's Jet Propulsion Laboratory through the Deep Space Network, or DSN.)
"Although Voyager 1 still is inside the sun's environment, we now can taste what it's like on the outside because the particles are zipping in and out on this magnetic highway," said Edward Stone, Voyager project scientist based at the California Institute of Technology, Pasadena. "We believe this is the last leg of our journey to interstellar space. Our best guess is it's likely just a few months to a couple years away. The new region isn't what we expected, but we've come to expect the unexpected from Voyager."
So what's it like on this magnetic highway? Voyager 1 reports back that solar winds have slowed to zero, and the magnetic field is about 10 times more intense than before the termination shock, which it crossed in December 2004.
Here's a fun animation, courtesy of NASA, of Voyager 1 on the magnetic highway: