Voyager 1 Finds Unexpected Wrinkles At the Edge Of the Solar System

Voyager 1 has been close to the boundary of the solar system for quite a while; we've mentioned that the edge is near a few times before, including an evidently premature report in 2010 that Voyager had reached a distance so far from the sun that it could no longer detect solar winds and another in 2011 that it had reached an "outer shell" of solar influence. It turns out that the boundaries of the solar system are fuzzier than once anticipated; the L.A. Times is reporting that "Toward the end of July 2012, Voyager 1's instruments reported that solar winds had suddenly dropped by half, while the strength of the magnetic field almost doubled, according to the studies. Those values then switched back and forth five times before they became fixed on Aug. 25. Since then, solar winds have all but disappeared, but the direction of the magnetic field has barely budged." Also at Wired, which notes "That's hard to explain because the galaxy's magnetic field is thought to be inclined 60 degrees from the sun's field. No one is entirely sure what's going on. ... [It's] almost as if Voyager thought it was going outside but instead found itself standing in the foyer of the sun's home with an open door that allows wind to blow in from the galaxy."

Comments

XKCD

[NobleSavage]

Obligatory XKCD

Re: XKCD

[tysonedwards]

The only thing that is shocking to me is the belief amidst the cited astrophysicists that once passing the heliosheath that there would be "uniform, high intensity cosmic radiation" as opposed to "non-uniform directional radiation". Our solar system is a very tiny dot versus a ginormous amalgamation of radiation sources at the center of our galaxy. It seems HIGHLY intuitive that the center of our galaxy would be a single, highly directional radiation source that would dwarf the very distant radiation sources.

Re:XKCD

[Anonymous Coward]

http://science.slashdot.org/story/13/06/30/1318227/voyager-1-finds-unexpected-wrinkles-at-the-edge-of-the-solar-system 30 June 2013
http://science.slashdot.org/story/13/03/20/1757256/voyager-1-officially-exits-our-solar-system 20 March 2013
http://science.slashdot.org/story/12/12/04/039257/voyager-1-so-close-to-interstellar-space-that-we-can-taste-it 03 December 2012
http://science.slashdot.org/story/11/12/07/2127247/voyager-1-exits-our-solar-system 07 December 2011
http://science.slashdot.org/story/05/09/26/1736216/voyager-1-sends-messages-from-the-edge 26 September 2005
http://science.slashdot.org/story/05/05/24/2334240/voyager-1-crosses-the-termination-shock 25 May 2005
http://science.slashdot.org/story/03/11/05/2019204/voyager-1-reaches-interstellar-space 05 November 2003

This has been going on for nearly 10 years. Arrghh!

Re: XKCD

[Anonymous Coward]

Our solar system is a very tiny dot versus a ginormous amalgamation of radiation sources at the center of our galaxy.

Actually, by analysis of cyclotron emissions, there are plenty of far more local galactic cosmic ray sources. The problem with something like Sagitarrius A* or something else near the center of the galaxy, is that is very far way for the energy scales being measured. Because cosmic rays are charged particles and there is a background magnetic field in the galaxy, such particles could not make a straight line from the center of the galaxy to here and instead would be trapped and susceptible to interaction with things in between. Even when you get into the TeV range of particles (the ones voyager was looking at was 2 MeV to 600 MeV), the gyroradius is on the order of dozens of AU.

This problem means that except at the highest of energies for extra-galactic cosmic rays, the direction of cosmic rays are scrambled and not pointing back to their source. The distribution of galactic cosmic rays has more to do with the magnetic field structure in the near by neighborhood. Additionally, in this case here, it has a lot to do with the interaction of high energy particles and shock waves in plasma, which is still a big, active area of research. This would determine how much is emitted or blocked by the heliosheath, but would also still depend on the structure of the area which is quite turbulent. An understanding of the interaction between the solar wind, very local sources like other near by stars and previous novas in the area is what this will come down to, and very little to do with the center of the galaxy.

It makes perfect sense.

[neoshroom]

Unexpected? You didn't think something 4.5 billion years old would have a few wrinkles?

Not too surprising

[Mr Z]

Someone else (who I think I saw here on Slashdot the last time Voyager was mentioned) had a great analogy for what we're likely seeing. I can't take credit for this at all, but I think it makes a lot of sense.

Suppose we're a small probe, making our way off an island, down the beach, and into the ocean. All we have is a wind-speed detector, and a water detector. As we near the water, waves start lapping over us. When they do, our wind-speed detector says "no wind", and our water detector says "we're wet." Have we entered the ocean yet? The answer is "not quite, but we're really darn close."

It doesn't seem surprising to me at all that the boundary neither perfectly uniform, nor stationary in time. I think we'll be in this transition band for a while.