Voyager 1, the Little Space Probe That Could, has been tantalizing scientists for a year now with the question of where it is. Which is not to say we’ve lost it — we know exactly where it is — but we don’t know what that where is.
Last July, the astronomy world was agog with the possibility that Voyager 1 had actually left the heliosheath — meaning, the envelope around most of our solar system where solar winds, constantly blowing out from our sun, maintain their speed and heading.
Scientists had long envisioned [the heliosphere’s] outermost layer, the heliosheath, to be a curved, distinct boundary separating the solar system from the rest of the Milky Way. They theorized that once Voyager 1 crossed that threshold, three things would happen: The sun’s solar winds would become still; galactic cosmic rays would bombard Voyager from every angle; and the direction of the dominant magnetic field would change significantly because it would be coming from interstellar space, not the sun.
It’s always good to have a checklist, right? And at the end of July 2012, Voyager 1 did indeed enter a region of space where the solar winds practically shut off, while the magnetic field’s strength nearly doubled. Score! But wait — then the readings changed, and the solar winds picked up again while the magnetic field strength lessened. No score. But wait! Then the readings changed again — five times altogether, before settling on August 25. Now the solar winds are pretty much gone, but the magnetic field’s strength and direction are not what anyone expected.
“The jumps indicate multiple crossings of a boundary unlike anything observed previously,” a team of Voyager scientists wrote in one of the studies. They labeled the new area the heliosheath depletion region.
Okay, the first rule of science ought to be that when you discover something your models didn’t account for, and you have to name it, you should at least give it a cool name. “Heliosheath depletion region” sounds like something Viagra might fix.
And then it got weirder. Remember those cosmic rays that were supposed to be “bombarding Voyager from every angle”? Well…
Voyager 1 detected an increase in galactic cosmic rays — but found that at times they were moving in parallel instead of traveling randomly.
“This was conceptually unthinkable for cosmic rays,” said Stamatios Krimigis, a solar physicist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., and leader of another one of the studies. “There is no cosmic ray physicist I know who ever expected that they would not all be coming equally from all directions.”
Time to give this new region a name, too! They’re calling it the “magnetic highway,” so now I’m envisioning Voyager 1 on a road trip, with a bunch of Motown songs playing on its 8-track tape recorder. (Voyager 1 was launched in 1977, and yes, it records its data on an 8-track. Don’t knock it, that thing has lasted 36 years and counting.)
JPL put out a short video explaining this magnetic highway, which went a long way toward helping me conceptualize it. This is weird and very cool stuff. Voyager 1 has been turning everyone’s expectations on their heads for a year now, and it’s a story that is still being written.
(Top image from NASA/JPL.)