Despite traveling 36 years and 11 billion miles (18 billion kilometers) from home, the intrepid Voyager 1 spacecraft still has not left the solar neighborhood. But all indications are that it is now crossing a major threshold to the rest of the galaxy. (Related: “Voyager at the Edge: Cosmic Roadtrip Hits Milestone.” )
New research published this week in the journal Science offers tantalizing clues about Voyager’s current location at the edge of the solar system, or heliosphere—the bubble-like boundary that divides the realm of the sun’s influence from interstellar space.
The specific region Voyager is currently sailing through has been dubbed the “magnetic highway.” It’s located within the outermost part of the heliosphere’s border, called the heliosheath. A confusing place, this highway is where there appears to be a connection between the solar and interstellar magnetic lines, and is where the flow of charged particles moves in and out of the solar system.
Newly released Voyager data from August 2012 indicate its instruments had detected the solar wind—the particles emanating from the sun—that had been buffeting the spacecraft for nearly four decades practically flat-lined. At the same time, sensors detected skyrocketing levels of incoming galactic particles from outside the solar system. These cosmic rays are thought to originate from the violent explosions given off by dying stars that go supernova.
“This strange, last region before interstellar space is coming into focus, thanks to Voyager 1, humankind’s most distant scout,” said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena.
“We saw a dramatic and rapid disappearance of the solar-originating particles. They decreased in intensity by more than a thousand times, as if there was a huge vacuum pump at the entrance ramp onto the magnetic highway,” said Stamatios Krimigis, the chief scientist in charge of Voyager’s low-energy charged particle instrument, in a press statement . “We have never witnessed such a decrease before, except when Voyager 1 exited the giant magnetosphere of Jupiter, some 34 years ago.”
Still in the Neighborhood
On its own this might have been considered key evidence that Voyager was about to make its exit from the solar system. But the on-board magnetometer paints a different picture. It is still detecting faint traces of the solar magnetic field, clearly indicating to mission scientists that the space probe is still within the realm of the sun. What they are waiting for now is for Voyager to detect an abrupt change in the direction of the magnetic field—which would indicate it’s originating from interstellar space and not from the sun.
“If you looked at the cosmic ray and energetic particle data in isolation, you might think Voyager had reached interstellar space, but the team feels Voyager 1 has not yet gotten there because we are still within the domain of the Sun’s magnetic field,” said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena in a NASA press release.
How long will it take for Voyager 1, traveling at 38,000 miles per hour (61,115 kilometers per hour), to officially exit our solar neighborhood? It really depends on the width of this strange transition zone it’s currently crossing. NASA scientists estimate it could take anywhere from a few months, to even years—but no one knows.
“But the wait itself is incredibly exciting, since Voyager continues to defy predictions and change the way we think about this mysterious and wonderful gateway region to the galaxy,” said Krimigis.
When it does come out on the other side, it will make history by becoming the first human-made object to leave the solar system and enter the realm of the stars and the rest of the Milky Way.