Chill Out, People: We Still Do Not Know If Voyager 1 Has Left the Solar System

The official position remains that the spacecraft has not yet crossed over into interstellar space



For 35 years, a spaceship built here on this planet has been flying away from our planet. And today, on this momentous day of March 20, 2013, the American Geophysical Union put out a press release announcing that *it* had finally happened: Voyager 1 had left the solar system, as indicated by "sudden changes in cosmic rays."

Could it really be?

Well, it *could* really be, but the official position of the Voyager team remains that Voyager 1 has not yet left the heliosphere, Donald Gurnett who has worked on Voyager since the 1970s, told me. Within a number of hours, AGU backtracked, releasing a correction minutes ago calling the location of Voyager 1 "a new region of space."

Why the confusion? The paper in question concludes that the intensities of anomalous cosmic rays (ACR) and galactic cosmic rays (GCR) shifted dramatically on August 25, 2012, and that these shifts "indicate that V1 has crossed a well-defined boundary for energetic particles at this time possibly related to the heliopause."

And that's for sure true: Voyager 1 did indeed experience dramatic changes in late summer, as we examined in a piece this past October. Here's a chart of the sharp drop-off in solar particles hitting the probe:


And here's what the probe saw cosmic rays do, something you would expect to see in interstellar space, outside of the bubble of solar wind around our star:


But one "well-defined boundary" does not interstellar space make. Before we can draw that conclusion, we need to see Voyager's magnetic field data, where scientists are hoping to see a change in the direction of the magnetic field. That data doesn't appear in this paper. To the contrary, the authors write that this still needs to be examined, "Future study of the variations of the remaining nuclei below ~10 MeV after 2012.78 and magnetic field data will help to determine whether this component is really a part of a low energy galactic component, or whether it is a weak 'halo' of ACR around the heliosheath region." (emphasis added)

As NASA spokesperson Jia-Rui Cook told Universe Today, "Our last statement about this was the critical thing we were looking for was a change in the magnetic field data." She continued, "This paper does not appear to address the magnetic field data."

Until we see that, we can't say for sure that Voyager 1 has "left the solar system" (technically we're talking about the heliosphere -- the bubble of solar winds around our star), all we can know is that, as the paper's authors put it, Voyager 1 has crossed a "well-defined boundary." I'm not saying that's not exciting -- it definitely is -- but it's also something that we've known for months.

The thing is, we don't know what the transition to interstellar space is going to be like -- there may be cliffs and boundaries and chasms of all kinds. After all, we've never crossed into interstellar space before.

That said, Voyager *is* on its way out, and we'll have cause for celebration (or what have you) soon enough.

Update, 2:34 pm: NASA has released a statement:

"The Voyager team is aware of reports today that NASA's Voyager 1 has left the solar system," said Edward Stone, Voyager project scientist based at the California Institute of Technology, Pasadena, Calif. "It is the consensus of the Voyager science team that Voyager 1 has not yet left the solar system or reached interstellar space. In December 2012, the Voyager science team reported that Voyager 1 is within a new region called 'the magnetic highway' where energetic particles changed dramatically. A change in the direction of the magnetic field is the last critical indicator of reaching interstellar space, and that change of direction has not yet been observed."