Voyager-1 hits mystery zone on road to intergalactic space
As Voyager-1 whizzes through this unchartered frontier, a place
so distant that charged particles from the sun have virtually
disappeared, astronomers are struggling to make sense of the
steady stream of data being returned to Earth.
Astronomers initially believed Voyager-1, which is about 11 billion miles from earth, had reached interstellar space on August 25, 2012, becoming the first man-made vehicle to breach the threshold of our solar system. But feedback from the spacecraft, which showed that the sun’s magnetic field was still exerting its influence on the probe, quickly cooled that theory.
As it turns out, the craft is still in the sun’s house, so to speak, standing on the porch with the endless galaxy beyond.
If Voyager-1 had really entered interstellar space, physicists say, the direction of the magnetic field would be different.
"If you looked at the cosmic ray and energetic particle data in isolation, you might think Voyager had reached interstellar space,” said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena, “but the team feels Voyager-1 has not yet gotten there because we are still within the domain of the sun's magnetic field."
Stone first explained the discovery of this unexpected zone during a lecture at the American Geophysical Union last year. A collection of papers published on Thursday in the journal Science put the findings into perspective.
In 2004, Voyager-1 reached a highly charged region known as the
heliosphere, a bubble-shaped region surrounding the solar system
where particles move in all directions due to solar winds. It was
anticipated this would be the final leg of the trip before the
spacecraft broke free of our solar system and entered
"You can never exclude a really peculiar coincidence, but this was very strong evidence that we're still in the heliosphere,” Voyager scientist Leonard Burlaga, the lead author of one of the papers, based at NASA's Goddard Space Flight Center, told Reuters.
Measuring the size of the heliosphere is also part of the Voyager mission.
Scientists believe that Voyager-1 journeyed into something of a magnetic boundary zone, where particles from inside and outside the solar system interact, but where the gravitational pull of the sun remains dominant.
"A day made such a difference in this region with the magnetic field suddenly doubling and becoming extraordinarily smooth," said Burlaga, "But since there was no significant change in the magnetic field direction, we're still observing the field lines originating at the sun."
NASA has got a lot of mileage out of Voyager-1 and its sister spacecraft Voyager-2, which were launched 36 years ago to collect data on Jupiter and Saturn and their respective moons. After completing their mission, the vehicles were sent hurtling toward interstellar space for what will certainly be their last mission.
Voyager-1 is heading in the direction of a star known to astronomers as AC +793888, but it will only get to within two light-years (one light year equals the distance that light travels in one year) before its nuclear energy source depletes itself sometime in the next decade. Voyager-2, meanwhile, is exiting the solar system from a different direction, and has not experienced the same phenomena.
"Voyager-2 has seen exactly what the models predicted we would see, unlike Voyager 1, which didn't," said Stone.
Voyager 1 may be in a unique place where the heliosphere and interstellar space interconnect, he added.