Back in 2013, NASA announced that Voyager 1 had finally, once and for all, left the heliosphere. In fact, their calculations showed that it had left in 2012. Not everyone agrees, though.

While NASA's official position is that Voyager 1 is now traveling through interstellar space, the truth is it's hard to know for certain — after all, nothing has ever left the solar system before, so it's hard to tell exactly what leaving looks like.

On one hand, as Merav Opher (the astronomer and Voyager team member we talked to in our Escape episode) explains, there's "been detection of radio waves on board of Voyager that are indicators of a density that can only be reached at the interstellar medium outside our solar system." And that led the Voyager team to conclude that, yay! We're out. But on the other hand, scientists were expecting a change in the magnetic field readings that haven't happened: "a year later the magnetic field still behaves as if we didn't leave the solar system," says Opher. But! She argues that the magnetic field outside the solar system will "drape," which explains the readings. Though she admits, "this is still a debate."

Meanwhile, two scientists working with Voyager have drawn up a new test aimed at putting the in/out controversy to bed within the next two years. The test hangs on detecting that expected magnetic field reversal — and if it doesn't happen within about two years, it probably won't...meaning Voyager 1 has already crossed over after all.

Read more:

This article from Forbes sums up both sides of the divide really well: Voyager Scientists Disagree On Whether Craft Has Reached Interstellar Space
For more nitty-gritty (including some great diagrams), head to NASA's Voyager Interstellar Mission section.