Voyager 1 has reached yet another new frontier on its historic journey towards the edge of our solar system. NASA scientists believe this “magnetic highway” represents the final region the spacecraft must cross before becoming the first man-made object to reach interstellar space, an event they are guessing could be as close as a couple of months away.

After Voyager 1 crossed the termination shock into the outer layer of the heliosphere known as the heliosheath in December 2004, the stream of charged particles from the sun (known as the solar wind) abruptly slowed down from supersonic speeds and started bouncing around in all directions. In June 2010, when it was about 17 billion kilometers (10.7 billion miles) from the sun, the outward speed of the solar wind finally slowed to zero and the intensity of the magnetic field experienced by the spacecraft also began to increase.

On July 28, 2012, data from Voyager 1’s onboard instruments that measure charged particles showed the spacecraft had entered a new region for the first time. Here, our sun’s magnetic field lines are connected to interstellar magnetic field lines, which allows lower-energy charged particles originating from the sun to zoom out and higher-energy particles from interstellar space to stream in – hence the “magnetic highway” moniker. The region ebbed and flowed towards Voyager 1 several times before becoming stable on August 25.

"If we were judging by the charged particle data alone, I would have thought we were outside the heliosphere," said Stamatios Krimigis, principal investigator of the low-energy charged particle instrument, based at the Johns Hopkins Applied Physics Laboratory, Laurel, Md.

However, the Voyager team believes it is still inside the heliosphere because the direction of the magnetic field lines hasn’t changed. They expect this to change once Voyager 1 crosses over into interstellar space.

"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."

Now about 18 billion kilometers (11 billion miles) from the sun, Voyager 1 is the most distant human-made object, with a signal from the spacecraft taking approximately 17 hours to travel to Earth.

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