Voyager 1 Still Hasn't Left the Solar System

Space lovers around the world were buzzing on Wednesday when the American Geophysical Union released a statement saying saying the Voyager 1 probe has finally left the heliosphere. Turns out that’s not entirely true, but the probe is getting closer.

One of a set of twin probes, Voyager 1 was launched on September 5, 1977. It followed a trajectory that took it flying by Jupiter then Saturn. After leaving the latter planet on December 14, 1980, it began its interstellar mission; its trajectory took it out of the plane where all the planets orbit. After flying by the latter planet, it  before flinging out of the plane on which all the planets orbit. But just because it suddenly had no more targets didn’t mean its mission was over. Voyager 1 is still functioning and it hasn’t slowed down. The furthest probe from the Earth, it’s still giving scientists groundbreaking insight into a completely unchartered realm of space.

Voyager 1 is still approaching the edge of our Solar System. All the bodies in our system are enclosed in a sort of bubble created by the solar wind’s energetic particles called the heliosphere. Beyond the heliosphere is the interstellar medium of gas and dust, an area scientists would love to have in situ measurements form. And that’s the goal – keep Voyager up and running so we can explore this part of the universe.

In 2004, Voyager 1 hit the outer sphere of the solar system in 2004 and passed into the heliosheath, a region where the supersonic solar wind slows and becomes turbulent. In December, 2012, the probe reached what scientists call the magnetic highway, a region where the magnetic field lines from the sun connect with the magnetic field lines emanating from interstellar space. This connection causes energetic particles from distant and other cosmic events to travel inside the solar system at the same time as the less-energetic solar leave.

As Voyager passed through the magnetic highway, scientists noticed that the magnetic field strengthened but its direction never changed. This is significant. Many suspect that the magnetic field will change direction when the probe enters interstellar space, but so far Voyager hasn’t detected the anticipated shift.

But the big change was registered on August 25, 2012. More than 11 billion miles from the Sun, Voyager 1 noted a drastic change in radiation levels. Cosmic rays trapped in the outer heliosphere all but vanished and galactic cosmic rays – cosmic radiation originating from a point outside our Solar System – spiked to levels the spacecraft has never seen. It’s consistent with what scientists expect to see when Voyager 1 does cross into interstellar space, a boundary point professor emeritus of astronomy at New Mexico State University in Las Cruces Bill Webber calls the heliocliff. It was these findings that were published in Geophysical Research Letters, a journal of the American Geophysical Union. That the paper appeared in a peer-reviewed journal made the news official.

But it turns out there’s little certainty that Voyager has actually metaphorically jumped off the heliocliff. Scientists are still debating whether the probe has left the Solar System or just entered some as-of-yet undefined region beyond it but still within the heliosphere. The trouble is that it’s nearly impossible to pin point just when the spacecraft will make the leap into interstellar space, which sort of accounts for all the false alarms we’re getting about it leaving the Solar System.

Corrected press releases started popping up all over the internet within hours of the AGU’s initial statement. Unfortunately for the scientists issuing these statements, it’s extremely hard to predict just when the probe will cross over; some mission scientists say it will happen anywhere from a few months from now to a few years.  We’re in an entirely unknown region of space here, something we already don’t know too much about.

But it’s only a matter of time before we see a press release stating it’s left the solar system and there won’t be corrections issued in the days that follow, and that will be awesome. For now, XKCD nailed it.