CHICAGO – NASA’s Voyager 1 spacecraft has encountered a “magnetic highway” at the edge of the solar system, a surprising discovery 35 years after its launch, the experts behind the pioneering craft said Monday.
Earlier this year, a surge in a key indicator fueled hopes that the craft was nearing the so-called heliopause, which marks the boundary between our solar system and outer space.
But instead of slipping away from the bubble of charged particles the sun blows around itself, Voyager encountered something completely unexpected. The craft’s daily radio reports sent back evidence that the sun’s magnetic field lines was connected to interstellar magnetic fields. Lower-energy charged particles were zooming out and higher-energy particles from outside were streaming in.
They called it a magnetic highway because charged particles outside this region bounced around in all directions, as if trapped on local roads inside the bubble, or heliosphere.
“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, a Voyager project scientist based at the California Institute of Technology. “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.”
Voyager is now 18 billion km away from the sun, which is 122 times the distance from the Earth to the sun. Yet it takes only 17 hours for its radio signal to reach us.
Scientists began to think it was reaching the edge of our solar system two years ago when the solar winds died down and particles settled in space the way they would in a swamp. An increase in the number of cosmic rays in May also led them to believe Voyager had approached interstellar space.
In July, the reading changed again, and by Aug. 25 Voyager was on the magnetic highway. The number of particles from the outside jumped sharply and the number of particles from the inside fell by a factor of 1,000.
“It is as if someone opened the floodgates and they were all moved down the river, also some boaters powered upstream with close to the speed of light have been able to get in at last,” said Stamatios Krimigis, Voyager’s principal investigator of low-energy charged particles.