Voyager 2 May Be Leaving the Solar System Soon, NASA Says
This NASA diagram illustrates the hypothesized positions of Voyagers 1 and 2 in the solar system as of October 2018. Voyager 1 reached interstellar space in 2012. Voyager 2 may soon hit that milestone.
Credit: NASA/JPL-Caltech

Want to get away? Want to get far, far away? Voyager 2 has you beat: The spacecraft, launched in 1977, is approaching the edge of the solar system, according to a NASA statement released today (Oct. 5).

That announcement is based on two different instruments on board, which in late August began noticing a small uptick in how many cosmic rays — superfast particles pummeling the solar system from outer space — were hitting the spacecraft. That matches pretty well with what Voyager 1 began experiencing about three months before its own grand departure in 2012, but scientists can't be sure of the milestone until after it has been passed.

"We're seeing a change in the environment around Voyager 2, there's no doubt about that," Voyager Project Scientist Ed Stone, a physicist at Caltech, said in the statement. "We're going to learn a lot in the coming months, but we still don't know when we'll reach the heliopause. We're not there yet — that's one thing I can say with confidence." [Voyager at 40: 40 Photos from NASA's Epic 'Grand Tour' Mission]

The team behind Voyager 2 knows that the spacecraft is currently almost 11 billion miles (17.7 billion kilometers) away from Earth. But it's hard to predict when the spacecraft will actually leave the solar system by passing through what scientists call the heliopause.

The heliopause is the bubble around our solar system formed by the solar wind, the rush of charged particles that constantly streams off our sun. But that solar wind ebbs and flows over the course of the sun's 11-year cycle, which means that the bubble of our solar system itself expands and contracts.

And because Voyager 2 isn't following precisely in its predecessor's steps, scientists aren't positive that its cosmic exit will result in identical changes to the data that the spacecraft reports. So until Voyager 2 passes through the heliopause, there's no way to be sure precisely where it is with regard to the heliopause.

Whenever it does successfully flee the solar system, Voyager 2 will become just the second human-made object to do so.

Email Meghan Bartels at mbartels@space.com or follow her @meghanbartels. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.