Has Voyager 1 reached interstellar space or not? That question was first asked about a year ago, when the probe first started seeing a drop-off in the levels of energetic particles emitted by the Sun, accompanied by a rise in cosmic rays from interstellar space. But the models of the Solar System's edge had suggested that there should be a corresponding change in the magnetic field's orientation as the Sun's field is overwhelmed by that of the galaxy as a whole. And Voyager 1 is seeing nothing of the sort; even as particle levels flip-flopped several times, the magnetic field remained largely stable.

There have been a couple interpretations of this. The scientists who first announced the results argued that the data showed evidence that a new, previously unpredicted region exists at the edge of the Solar System and that we would have to wait before we would be able to sample the interstellar magnetic field. But later that year, a different team argued that the probe was in interstellar space. It's just that interstellar space wasn't looking like we expected.

Now, a new paper has come out that revisits the cause of the problems: the models of the magnetic fields that exist where there's a complex interaction between two magnetic fields and two different flows of charged particles colliding. Earlier models of this region had been the ones that suggested the orientation of the magnetic field would change as the interstellar field wrapped gently around the one generated by our Sun. The new one, however, suggests that the interstellar field lines run directly up against the ones from our Sun, at which point they execute a nearly right-angled turn, leaving the two sets to travel parallel.

In this model, there is no significant change in orientation to be seen as Voyager moves across the last of the Sun's magnetic field lines and into the first of the interstellar ones. However, the model shows that the changes in the source of particles occurs during this transition. Since Voyager 1 has experienced those changes, it's probably in the interstellar medium.

The authors admit that their model has some important limitations—one big example is that the simulation is only two-dimensional, which is fairly limiting. And NASA was quick to issue a press release pointing out that this shouldn't be viewed as a conclusive answer, but more as a contribution to a larger debate among scientists.

More important than the suggestions made by some squabbling scientists, however, is what this illustrates about the process of science. Before Voyager got there, we'd done the work to make a physically plausible model of what the edge of the Solar System should look like. But when it actually arrived, we found out that our models were clearly wrong. But Voyager hasn't said a thing about what, specifically, was wrong about them.

There seem to be two different schools of thought developing. One, exemplified by this new paper, wants to take the data at face value and come up with a new model that reflects what Voyager is seeing right now. A second seems to think that the older models may still largely be right, but not detailed enough. They capture the rough outlines of the edge of the Solar System, but not at a high enough resolution to see the weird behavior right at the edge. If Voyager hadn't actually wandered into it, we wouldn't have known it was there. Given a bit more time, Voyager will wander out, and we'll see what we've always expected and can just tweak our existing models a bit to have everything match the data.

The question now is how much time scientists are willing to give Voyager and whether they can get more detailed, three-dimensional models working in the meantime. In all probability, there will be a few more papers, along with some dueling press releases, before this is sorted out.

The Astrophysical Journal Letters, 2013. DOI: 10.1088/2041-8205/774/1/L8 (About DOIs).