Voyager 1 Left Solar System Last Year, Controversial Study Suggests

A new study suggests the Voyager 1 spacecraft, which has been flying on an outward-bound trajectory through the solar system since 1977, left the realm of the Sun's influence a year ago and has been passing through interstellar space.

Researchers from a team led by University of Maryland's Space Physics Group contend that the Voyager passed the scientific milestone last summer when it detected a drop in the numbers of particles coming in from the Sun and a rise in galactic cosmic rays coming from interstellar space. Previously, however, this event was not considered enough evidence and researchers have been waiting for the Voyager to detect a magnetic field that flows in a different direction than the magnetic field of the solar system to indicate the spacecraft has left the bounds of the solar system.

University of Maryland physicist Marc Swisdak suggests that the two great magnetic fields are aligned enough that the Voyager was able to pass between them without recording the anticipated directional change that would have marked the transition from our solar system to interstellar space.

Swisdak and his colleagues' findings run directly counter to recent papers published by NASA and other scientists, which have suggested the voyager is still in an ambiguous in-between zone and not properly out of the bounds of the solar system.

"It's a somewhat controversial view, but we think Voyager has finally left the solar system, and is truly beginning its travels through the Milky Way," Swisdak, who is the lead author of the new research published in The Astrophysical Journal Letters, said in a statement.

Voyager 1 and its sister probe Voyager 2 were both launched to study the outer planets. Voyager 2 is on a trajectory out of the solar system as well, but it is heading in a different direction than Voyager 1. The probes are powered by the decay of radioactive plutonium. Voyager 1 is expected to be completely out of power by 2025 and it will only have enough energy to operate its scientific instruments until 2020. Voyager 2 is expected to enter interstellar space in the coming years.

While there is consensus on how far Voyager 1 has traveled, not everyone agrees upon where it is. Officials from NASA contend the probe is still within the heliosphere, the "solar bubble" that marks the Sun's field of influence.

"We know where Voyager is in terms of distance and we know what it is observing. The challenge is relating that to these complex models of the interaction between the interstellar medium and the heliosphere," Edward Stone, NASA's Voyager project lead scientist told Reuters.

"Other models envision the interstellar magnetic field draped around our solar bubble and predict that the direction of the interstellar magnetic field is different from the solar magnetic field inside. By that interpretation, Voyager 1 would still be inside our solar bubble," Stone said in a NASA statement.

But Swisdak thinks that his predictions are correct and that Voyage 1's instruments will not detect this anticipated directional change in magnetic fields.

"If they see a strong shift in the magnetic field, a big jump, then that means that what we've outlined can't be correct," Swisdak told Reuters.

"I'm perfectly willing to be proven wrong here and if I were, that would be kind of cool. But it agrees with all the data that we have so far," he said.