At 11 billion miles away, NASA’s Voyager 1 spacecraft has traveled to the edge of the solar system.
Instead of breaking through into interstellar space, however, the 35-year-old spacecraft has found an entirely unexpected region scientists have dubbed the “magnetic highway.” That’s because the spacecraft is now being bombarded by both particles originated from the sun as well as cosmic rays from outside the solar system.
“This is like the beach at the edge of the ocean,” said Nick Suntzeff, an astronomer at Texas A&M University.
Launched in 1977, Voyager 1 and its counterpart Voyager 2, discovered Jupiter’s rings, volcanic activity on the Jovian moon Io and had close encounters with Saturn before traveling beyond Pluto’s orbit and farther into space than any human probe. Scientists expect it to continue to send data about conditions in deep space until its power runs out.
In recent months astronomers tracking data still being pinged back by the spacecraft observed several characteristic signs that the spacecraft had reached the edge of the solar system, and perhaps even exited it.
Most notably, they saw a rise in cosmic ray particles and a decrease in protons originating from the sun.
In yet another indication that the spacecraft had departed the solar system, the velocity of the solar wind had slowed down to zero. This stream of energetic particles originates in the upper atmosphere of the sun, and creates the heliosphere, an enormous bubble that surrounds the solar system.
To confirm the absence of a solar wind, amazingly, scientists commanded Voyager to perform a delicate, 70-degree turn to measure the solar wind in the up and down directions. It did so, even though it is 112 times the distance between the Earth and sun.
But that’s not the entire story.
To confirm that Voyager 1 has reached interstellar space, scientists have been looking for a change in the direction of the magnetic field.
Instead, when they looked at data about the magnetic field, they found a jump in the intensity in late August, but no change in its direction, which they expect when Voyager reaches interstellar space.
Instead Voyager appears to have entered the so-called magnetic highway, which scientists had not expected to find on the edge of the solar system.
“If we would have only looked at particle data alone, we would have said we’re out of the solar system,” said Stamatios (Tom) Krimigis, Voyager’s principal investigator for low-energy charged particles. “But nature is very imaginative, and Lucy pulled up the football again.”
So when will Voyager venture into the great unknown?
Scientists believe it must come soon, but given the surprises they’ve found so far from the sun, they’re not placing any hard bets.
“It’s hard to predict, but our experience would suggest it is a couple of more years,” said Edward Stone, Voyager project scientist, from the California Institute of Technology.
It had better come soon. As Voyager’s nuclear power source decays, it loses about 4 watts of power a year. By 2020, scientists say they will have to begin turning off some of the four remaining functioning instruments aboard the spacecraft.
And five years later the spacecraft will have power only to make a few, final pings home before it dies. But even that won’t be the end.
As it flies away from the sun, Voyager will remain under its gravitational influence for another 40,000 years until it starts to come under the influence of other stars.