For at least a year now, NASA has been waiting with bated breath for Voyager 1 to pass through the boundary of our solar system and become our first emissary to the stars. It’s been cruising the edge for some time, but when it finally leaves forever, it won’t be a satisfyingly clear punch-through — so it’s hard to say exactly when this will happen. Or happened. Now the spacecraft is in another strange new zone, where the influx of cosmic particles has been ramping up by the week.
These particles mean Voyager 1 is at the frontier, according to project scientist Ed Stone, who has been working with the spacecraft since it and its twin launched in 1977. Voyager 1’s high-energy telescopes are watching charged particles, created when distant stars went supernova. Some of these particles make their way into our solar system, riding along magnetic currents that bring them in toward the sun and us, but for the most part the sun deflects them. Now it is deflecting fewer and fewer at the spacecraft’s location 11.1 billion miles from home. Voyager’s radio signals take 16 hours and 38 minutes to reach Earth.
From January 2009 to January 2012, the spacecraft noticed a gradual 25 percent increase in these cosmic rays. Then starting on May 7, the cosmic ray hits started going up — 5 percent in a week, and 9 percent in a month, NASA says. That’s a sign that Voyager is almost away from the sun’s sphere of influence.
It’s even possible that it’s already gone. Scientists are still crunching two other sets of numbers that will help prove it: The magnetic field surrounding the spacecraft, which will switch directions when it exits, and the amount of solar particles blown out by the sun, which has dropped but hasn’t stopped. It’ll be a historic moment when that finally happens — or when the numbers show that it already has.