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Voyager 2 Detects Peculiar Solar System Edge
ClickOnThis writes "CNN reports that Voyager 2 has detected evidence of the magnetic edge of the solar system (aka the heliopause) at 76 AU (1 AU = 93 million miles), much closer to the Sun than the location of 85 AU found by Voyager 1. From the article: 'This implies that the heliosphere, a spherical bubble of charged low-energy particles created by our Sun's solar wind, is irregularly shaped, bulging in the northern hemisphere and pressed inward in the south. [...] The researchers think that the heliosphere's asymmetry might be due to a weak interstellar magnetic field pressing inward on the southern hemisphere.'"
I believe from the Voyager I expedition that Voyager I detected and eventually cross the heliosphere where it was detected a year later. So the idea that the size stayed steady during the time then quickly switched sizes as Voyager II approached is unlikly... Unless the excape of Voyager I has upset the Gods... Then we are all doomed!
no, we've been taking data over many years along two different parabolic trajectories, that's a HUGE difference from sampling at two little data points. And we'll keep taking data along these curves; expansion or contraction and other variations could possibly be detected
Hmmm, irregular and off-center. If the sun is moving at a given speed, the overall shape of the heliosphere would appear warped and off center... probably egg shaped. That might explain the difference.
North and south also refer to magnetic poles. North is generally assumed to be the positive pole, and south the negative, though when poles flip, as happens on earth (every one million years I think), and the sun (every 11 years or so, sometimes refered to as a period of solar maxima), common usage north and south probably won't switch. Wikipedia has a bit more info.
There's also galactic north and south, which are imaginary axes perpendicular to the the plane of the galaxy. Again, wikipedia has more info.
I'd hazard that what this article refers to as north is probably some assumed "solar north" roughly parallel to Earth's north.
Actually there is more information available than just two data points. There is the a priori knowledge of how magnetic fields and plasmas behave, the cumulative measurements of the two Voyager probes up to now along their trajectories, the measurements of other spacecraft over many decades of space research, and other observations of particles in interstellar space. All of this contributes to the model one infers for the shape of the field. Also, see my earlier post.
If it weren't for deadlines, nothing would be late.
Could it not simply mean that it changes in size? I'd be surprised if it *didn't* change in size, based on all the variable energy in the solar system. The sun changes, the planets change place, etc.
That's actually very likely taken into account. When Voyager 1 found the heliopause, they were pretty sure that the termination shock was moving inward fairly rapidly due to it being past solar max, and so Voyager 2 would catch it pretty soon. This sounds like it happened quicker than their predictions expected. See here for more details. Note that they thought at the time that Voyager 2 might encounter the shock in 2005, but it might actually not catch it at all (as it might start moving outward again).
I saw the guy mentioned in the article (Ed Stone) give a talk on Voyager 1's results, so I'm pretty sure he'd know, especially since he, y'know, mentioned it.
Yup.
Someone once explained the heliopause neatly by pointing to the splash-disk of water in a sink, with the tap turned on full. The water coming from the tap pushes out, while the water already in the sink is trying to return to the middle to go down the drain.
Hence, you get a 'circle' where the energy of the tap water (coming out from the center) = the energy of the material trying to fall back into the center. The circle isn't perfect; it moves as the tap outpouring is not uniform and varies quite a bit.
It's actually a pretty good analogy, since the topagraphy of the sink (as a parallel to the gravity environment) also affects that 'circle' significantly.
Much like that, I suspect that the heliopause is hardly static; it probably bulges and deflates dynamically with solar activity (once that reaches the periphery, of course).
-Styopa
It's fun to list a bunch of possibilities, but to answer the original question, the "southern hemisphere" is simply the part of the sky with negative Declination.
...from a far less clueless source.
Here is an illustration of the phenomenon.
-mcgrew
Can someone explain the slew of Global Warming related snarks and references? I mean, what the hell is similar between this and the other?
Global warming, we have a well understood and physically justified model whose conclusions are gradually confirmed by more and more evidence.
Heliopause, we have a naive model based on little evidence, whose conclusion - uniformity of the Heliopause based on lack of apparent altering factors - is refuted by two pieces of probably not very significant evidence. We have no historical evidence of how the heliopause has altered in the past for us to compare our data.
Global warming, we have a reasonable selection of known factors, and by seeing what effects they have on our model, we find that we cannot statistically reject GH gases as a significant issue.
Heliopause, we have almost no known factors that can cause this distortion, and on the basis of this, we only know that the present factors appear insufficient based on our conventional assumptions.
Global warming, we have a broad scientific consensus shown in all peer reviewed publications, questioned by only a few with dubious records of intellectual integrity and whose arguments have been shown to have hilarious errors over and over again.
Heliopause, we have no consensus, because this is a new question that no one has tried to answer yet. All anyone can do is throw hypotheses up in the air. And no, 'human effect' is not one of them because the Earth goes around and around so any effect on the heliopause would be averaged out, and because we don't exert any measurable influence that could affect such a massive thing. (Inverse square law applies, and everything)
So, in summary, I don't get the joke. If this is at all like climatology, then the analogy would be with climatology in the 19th century, where we've only just begun to try to understand the weather. In that case, history shows waiting a few years will not be enough. A century, maybe...
I forgot whose talk I heard yesterday (they changed the speaking order; session was SH22A) but basically: V1 passed the termination shock (NOT the heliopause; summary is wrong) at the end of 2004; this was the big announcement at last spring AGU meeting. Before that, they were seeing foreshock signatures (plasma and magnetic). V2 is now seeing those signatures, but seeing them a fair bit closer in than V1 was observing them. So, V2 has not passed the heliopause, nor even the termination shock, but appears to be nearing the TS closer to the Sun than V1 did. This is a surprising/interesting result, but not huge overturning of theory or anything. Learning the structure of the outer regions of the Solar System is the whole point of these exercises (and the upcoming IBEX mission).
The only reason comets have tails is because there is an outward pressure that forces ejected particles away from their source. Likely, the biggest way that such a 'tail' would form in the heliopause is if there was an external force pushing on it.
Think: Earth's magnetic field.
The magnetic field of the earth is shaped very much like a comet, but it is always pointed away from the sun and ripples as solar output changes. There is a website that seeks to model the fluxuations of the magnetic field, but I forget where it's at. If you can locate a source of what might be pushing on the the solar system's magnetic field, then it may be similarly shaped.
You expect the termination shock to be symmetric, with the Sun at the centre. There will be interstellar influences, but the Voyagers are still only a tiny fraction of a percent on their way even to Alpha Centauri.
Yes, there aren't many data points, but when the first two show the termination shock is not symmetric, so close to the solar system, there is clearly something else going on.
This Is Interesting (tm).
...laura, who was in high school when Voyager 2 was launched. Sigh.