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)