From NASA Science News January 15, 2010: Last year, when NASA’s IBEX (Interstellar Boundary Explorer) spacecraft discovered a giant ribbon at the edge of the solar system, researchers were mystified. They called it a “shocking result” and puzzled over its origin.
Now the mystery may have been solved.
“We believe the ribbon is a reflection,” says Jacob Heerikhuisen, a NASA Heliophysics Guest Investigator from the University of Alabama in Huntsville. “It is where solar wind particles heading out into interstellar space are reflected back into the solar system by a galactic magnetic field.”
Heerikhuisen is the lead author of a paper reporting the results in the Jan. 10th edition of the Astrophysical Journal Letters.
“This is an important finding,” says Arik Posner, IBEX program scientist at NASA Headquarters. “Interstellar space just beyond the edge of the solar system is mostly unexplored territory. Now we know, there could be a strong, well-organized magnetic field sitting right on our doorstep.”
The IBEX data fit in nicely with recent results from Voyager. Voyager 1 and 2 are near the edge of the solar system and they also have sensed strong* magnetism nearby. Voyager measurements are relatively local to the spacecraft, however. IBEX is filling in the “big picture.” The ribbon it sees is vast and stretches almost all the way across the sky, suggesting that the magnetic field behind it must be equally vast.
Although maps of the ribbon (see below) seem to show a luminous body, the ribbon emits no light. Instead, it makes itself known via particles called “energetic neutral atoms” (ENAs)–mainly garden-variety hydrogen atoms. The ribbon emits these particles, which are picked up by IBEX in Earth orbit.
Above: A comparison of IBEX observations (left) with a 3D magnetic reflection model (right). More images: data, model.
The reflection process posited by Heerikhuisen et al. is a bit complicated, involving multiple “charge exchange” reactions between protons and hydrogen atoms. The upshot, however, is simple. Particles from the solar wind that escape the solar system are met ~100 astronomical units (~15 billion kilometers) away by an interstellar magnetic field. Magnetic forces intercept the escaping particles and sling them right back where they came from.
“If this mechanism is correct–and not everyone agrees–then the shape of the ribbon is telling us a lot about the orientation of the magnetic field in our corner of the Milky Way galaxy,” notes Heerikhuisen.
And upon this field, the future may hinge.
The solar system is passing through a region of the Milky Way filled with cosmic rays and interstellar clouds. The magnetic field of our own sun, inflated by the solar wind into a bubble called the “heliosphere,” substantially protects us from these things. However, the bubble itself is vulnerable to external fields. A strong magnetic field just outside the solar system could press against the heliosphere and interact with it in unknown ways. Will this strengthen our natural shielding—or weaken it? No one can say.
Right: An artist’s concept of interstellar clouds in the galactic neighborhood of the sun. [more]
“IBEX will monitor the ribbon closely in the months and years ahead,” says Posner. “We could see the shape of the ribbon change—and that would show us how we are interacting with the galaxy beyond.”
It seems we can learn a lot by looking in the mirror. Stay tuned to Science@NASA for updates.
h/t to Leif Svalgaard
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Leif, thanks for the nice animations. The solar equatorial plane is around seven degrees off the invariant (orbital) plane at the moment, but the tilt looks to be considerably more. Why is that and what pulls the sheet back into line further out? And when it get’s pulled back into line, is it pulled back into line with the ‘orbital’ plane of the planets, or into line with the solar equatorial plane? And why does the HCS only exhibit this with the two lobed HCS and not when it is four lobed? Is it something to do with relative dominance in the dipole and quadrupole magnetic fields of the Sun?
Lot’s of questions…. sorry.
And a rogue apostrophe! Aaaargh!
Vukcevic,
I think we have been arguing over semantics. You say magnetic field lines do not exist, but I have not yet seen you argue that magnetism does not exist. You have not yet disagreed with my statement that magnetism from a star will fly away from it if the star collapses inside an event horizon.
Incidentally, your analogy with isobars is not a good one, since an isobar is just a line connecting points having the same pressure. There is no physical reason why we cannot plot an isobar of 1019.5 instead of 1020. This is not the case with magnetic field lines. The magnetic influences are concentrated along those lines and there is no smooth gradient between them as there is in isobars.
I’m no physicist, but I figured that out on my own just by thinking about it.
corrected version
kadaka (14:49:28) :
Oh, I’ve been glancing through the magnetism discussion. So a magnetic field in space does not “switch off” once the underlying current that generated it ends, once established it simply remains there until something “taps into” it, disturbing the field?
I have been thinking on this:
1) looking at Maxwell’s equations B=constant is a solution,( but I will check it with a theoritician.)
2) a magnetic field carries energy . In a superconducting magnet for example, all hell breaks loose if there is a short ( recent LHC short) . This happens if there is matter around. If there is no matter around the field? Conservation of energy says the field remains until it meets some matter. I could imagine a strong magnetic field of a star remaining after the star is swallowed in a black hole, like the grin of the Cheshire cat in “Alice in wonderland”. Or is it “through the looking glass”?
3) I can see a very long wave electromagnetic field, a standing wave in the universe, this would be independent of its source but would imply that it would have a corresponding electric field perpendicular to it .
Oh well, I was hoping we’d all be five times smarter once the Solar System got out of the interstellar cloud. 😉 Good dream while it lasted.
BTW sir I don’t understand why others find your style brusque. I’d be happy to learn from you.
tallbloke (00:49:57) :
The solar equatorial plane is around seven degrees off the invariant (orbital) plane at the moment, but the tilt looks to be considerably more. Why is that
The invariant plane has nothing to do with the ’tilt’
and what pulls the sheet back into line further out? And when it get’s pulled back into line, is it pulled back into line with the ‘orbital’ plane of the planets, or into line with the solar equatorial plane?
solar rotation is responsible, so the equatorial plane is the only one that counts.
And why does the HCS only exhibit this with the two lobed HCS and not when it is four lobed?
It is instructive to look at the historical record of how we figured out that there was a HCS. A good place to begin is http://www.leif.org/research/Model%20Polar-Sector%20Solar%20Magnetic%20Fields.pdf then http://www.leif.org/research/Sun%20Magnetic%20Sector%20Structure.pdf and finally: http://www.leif.org/research/A%20View%20of%20Solar%20Magnetic%20Fields%2C%20the%20Solar%20Corona%2C%20and%20the%20Solar%20Wind%20in%20Three%20Dimensions.pdf
In the last reference we put it all together and it marks the birth of our modern understanding of the HCS.
In a certain sense, it is incorrect to talk about a tilt [although we used the word ourselves]. To get a mental image of the situation consider a Sun that was not rotating and had four sectors of equal latitudinal extent. Then it is clear that you have a wavy brim around the Sun and a ’tilt’ is a misnomer. Now slowly make one of the four sectors weaker, i.e. decrease its latitudinal extent. This has the effect of making the brim lopsided [’tilted’], but the physics has not changed. The brim is just a bit asymmetrical. Then let the sector grow again and the brim rights itself. Now, all this takes place in the corona near the Sun. The solar wind carries the shape of the brim with it radially outwards.
Now, introduce solar rotation. First consider the four-sector case. A stationary observer near the solar equatorial plane [e.g. the Earth which can be considered almost stationary as it moves 14 times slower than the Sun rotates] would then be above the brim for a week [i.e. in a region with one magnetic polarity – that of the North Pole of the Sun], then below the brim for the next week and in the opposite polarity, then again above and finally below the last week of the four [a solar rotational period is about four weeks]. Let us assume that the latitudinal extent of the sectors were 30 degrees, then as long as we were less than 30 degrees away from the Sun’s equatorial plane we would see this alternation of polarities or sectors. If we were more than 30 degrees away from the equatorial plane we would be ‘above’ all this mess and see no sectors of changing polarities at all. This is what the Ulysses spacecraft going over the poles indeed observed, so a fine confirmation of our model. At the Earth, the rotation has only carried the warps about 60 degrees around the Sun [more correctly: the sun has rotated 60 degrees away from where it was when the solar wind we observe at Earth was emitted. If we move the observer out to six times the Earth’s distance [just a tad beyond Jupiter], the Sun would have rotated 6×60 = 360 degrees, i.e. the brim has wrapped itself once around the Sun. Out at 15 times that distance [15*6=90 AU] it would have been wound 15 times around [and for a four sector structure we would have had 4*15 = 60 crossings of the HCS moving from the Sun to the Heliopause].
Note that no ’tilt’ is involved. Now, as before, make one of the sectors weaker. The whole structure doesn’t tilt over, all that happens is that the latitude to which the weaker sector reaches is a little lower, say to 20 degrees. So, if we were observing at 27 degrees above the equatorial plane, instead of running into the brim four times as when all four sectors extended to 30 degrees, we would be skimming above the one that only reaches to 25 degrees and we’ll only run into the brim twice rather than four times. Now make the one sector even weaker [e.g. to the point where it has gone away] and you’ll see that we still only run into the brim twice [e.g. have a two-sector structure], but no tilt is involved, so as far as the ’tilt’ is concerned, the number of sectors doesn’t make any difference. The brim [or the HCS] is really NEVER tilted in any sense of the word because the Sun rotates so we’ll see whatever structure there is appearing all the way around the Sun, and multiple times as we move farther away. This, of course, means that there can be no ‘signature’ or mark of the HCS out where the Ribbon is, because the HCS moves around the Sun every 25 days, as in http://www.leif.org/research/HCS%20projected%20onto%20Heliopause.png
because the HCS moves around the Sun every 25 days, …
Note that the Ribbon does not move, it sits around the nose in a direction given by the movement of the Sun through the interstellar medium.
[Thanks Leif, I corrected the original for you already. RT – mod]
Leif Svalgaard (04:34:16) :
[Thanks Leif, I corrected the original for you already. RT – mod]
You actually read this stuff? 🙂
because the HCS moves around with the Sun every 25 days…
So if you were sitting on the Ribbon, you would see the HCS go by every week [for 4 sectors] or every two weeks [for 2 sectors]. And if the HCS is rather flat [as it is right now] you might be skimming over it and not see the HCS go by at all, just as Ulysses didn’t see any sectors [i.e. being overtaken by the HCS] when it went over the poles. Reading my long post, I see that I used the wording ‘running into the brim’. This is not the best way of expressing what happens: rather, it is the rotating brim that overtakes [or runs into] the observer. The end result is the same, of course.
Hi Leif, thanks for the detailed reply. I appreciate the point about the revolution of the waviness of the HCS every 25 days, I just wondered why you cited the spiral wrapping as a disproof of Vukevic’ interpretation.
I agree that since the ribbon curves more or less symmetrically around the nose of the heliosphere, it’s more likely something to do with the motion of the heliosphere wrt the interstellar medium. However I note Vuk’s comment about the current opposition between Jupiter and Saturn, whilst further noting that they are currently roughly in line with the nose and tail of the heliosphere, and as Vuk said, above and below the Solar equatorial plane. I don’t discount possibilities until enough data are in, so I hope the ribbon will continue to be monitored over the next few years while Jupiter does a 90 degree section of it’s orbit. Even though they unlikely to be the main cause of the waviness of the ribbon, it will be interesting to see if any modulation we can pick out coincides with their motion or not.
Regarding the waviness of the HCS in relation to the solar equatorial plane, I completely understand what you are saying about the closeness of Earth’s orbital plane to the plane of the HCS, but I still think your earlier comment about the ‘buckling’ and ’tilt’ of the HCS in the inner part of the solar system then returning to alignment further away from the Sun merits further investigation. I think the distinction of whether this is alignment with the orbital plane or solar equatorial plane is interesting and potentially important.
Further discussion getting underway here too for anyone interested.
http://tallbloke.wordpress.com/2010/01/18/force-orientation-in-our-part-of-the-galaxy/
tallbloke (05:02:17) :
Hi Leif, thanks for the detailed reply. I appreciate the point about the revolution of the waviness of the HCS every 25 days, I just wondered why you cited the spiral wrapping as a disproof of Vukevic’ interpretation.
Then I lost you too 🙁 The spiral is an effect of rotation. The same effect as I have just described. Nobody has said that the solar wind or the HCS moves in a spiral shape. [Although Solar Energetic Particles does follow the spiral as any particle that is not part of the solar wind expansion will have to do, as it is frozen to a field line and field lines have the spiral shape].
I think the distinction of whether this is alignment with the orbital plane or solar equatorial plane is interesting and potentially important.
No, this is not important. The alignment is completely determined by the local balance between magnetic and gas pressure and is observationally tied very strongly to the equatorial plane. The Rosenberg-Coleman effect is strong proof of this. See http://www.leif.org/research/Model%20Polar-Sector%20Solar%20Magnetic%20Fields.pdf and
http://www.leif.org/research/Asymmetric%20Rosenberg-Coleman%20Effect.pdf
The effect arises because of the 7 degree angle between the two planes and would disappear if the brim is aligned with the orbital plane rather than with the equatorial plane.
Wilcx and Scherrer’s analysis of this effect http://www.leif.org/EOS/JA077i028p05385.pdf shows that the phase of the effect is tied very strongly [‘to within a few days’ they said] to when the Earth crosses the solar equatorial plane.
So, there is no doubt that the HCS is aligned with the equatorial plane. This is an observational fact. BTW, analysis of the the ~40 years of data since the Wilcox/Scherrer paper fully confirms their conclusion.
tallbloke (05:02:17) :
I just wondered why you cited the spiral wrapping as a disproof of Vukevic’ interpretation.
Further on the spiral: if you could actually ‘see’ the HCS it would be a spiral wrapping around many times, just as in my original depiction: http://wso.stanford.edu/gifs/helio.tiff
The disproof comes from the fact that the spiral moves outwards all the time so its intersection with the heliopause sweeps around in 25 days, while the ribbon stays put. Now, it is possible that I have overestimated people’s ability to think things through, hence the very long explanation. I fear that for Vuk, the argument is too long to follow and that we’ll have to take very small steps so not to overtax available mental capacity.
Leif Svalgaard (05:43:22) :
Wilcx and Scherrer’s analysis of this effect http://www.leif.org/EOS/JA077i028p05385.pdf shows that the phase of the effect is tied very strongly [‘to within a few days’ they said] to when the Earth crosses the solar equatorial plane.
So, there is no doubt that the HCS is aligned with the equatorial plane. This is an observational fact.
Or to be more precise, it’s an observational fact at Earth’s orbital distance.
Thanks for the link, I’ll take a read. And by the way, I’ve been ploughing through the stuff you wanted me to read on Baryonic Acoustics. Fascinating.
tallbloke (06:14:25) :
Or to be more precise, it’s an observational fact at Earth’s orbital distance.
The solar wind is radially outwards from the Earth and out, so the alignment will be preserved. We know this from Ulysses and Voyagers and from the orientation of comet ion tails. There are no forces acting on the solar wind to change the orientation in the short time [~1 year] it takes to traverse the Heliosphere.
Leif Svalgaard (06:05:24) :
I fear that for Vuk, the argument is too long to follow and that we’ll have to take very small steps so not to overtax available mental capacity.
You were doing well up to this point. There is no need for this type of personal comment.
Clive E Burkland (06:50:56) :
You were doing well up to this point. There is no need for this type of personal comment.
I was expressing my fear [based on his past performance] and my willingness to accommodate him. I have always said that if one really understands something, one can explain it to a six-year old.
Leif Svalgaard (06:35:00) :
The solar wind is radially outwards from the Earth and out, so the alignment will be preserved.
Light is bent by gravity, so why not much heavier and slower particles in the solar wind?
Leif Svalgaard (07:18:34) :
Clive E Burkland (06:50:56) :
You were doing well up to this point. There is no need for this type of personal comment.
I was expressing my fear [based on his past performance] and my willingness to accommodate him. I have always said that if one really understands something, one can explain it to a six-year old.
Clive, I’ve been asked by Vuk to put up a thread for this topic on my blog where he won’t have to deal with this kind of comment.
http://tallbloke.wordpress.com/2010/01/18/force-orientation-in-our-part-of-the-galaxy/
tallbloke (07:21:41) :
Light is bent by gravity, so why not much heavier and slower particles in the solar wind?
We are now moving into pseudo-science. There is no gravity pulling a particle towards the invariant plane, because the solar wind particles [as I carefully explained] do not stay long enough in inner solar system for planetary perturbations to add up. Now, if a solar wind particle would hang around in the inner solar system for some millions of years that would be different, but as it doesn’t…
Leif Svalgaard (07:29:39) :
tallbloke (07:21:41) :
Light is bent by gravity, so why not much heavier and slower particles in the solar wind?
We are now moving into pseudo-science. There is no gravity pulling a particle towards the invariant plane
Uh Huh. Small perhaps, but non-zero. So, not pseudo-science at all.
My other question for you today is this:
Why does the Sun’s equator rotate faster than the polar latitudes?
In terms a six year old can understand please.
tallbloke (07:21:41) :
Light is bent by gravity, so why not much heavier and slower particles in the solar wind?
Apart from the forces being too small [you have to get really close to, say Jupiter – and you can’t because of its large magnetosphere], one might entertain the idea that Jupiter, for example, would act as a gravitational lens and concentrate the solar wind onto the Sun-Jupiter line. That might give rise to a point of enhanced density at the Heliopause, but not a ribbon. But, more importantly, the Heliopause is so far away that Jupiter would take up such a minute portion of the sky [less than 1/6000 of what it takes up seen from the Earth] that the effect [if it were there] would be infinitesimal. But, I realize that rational arguments may not carry much weight in this discussion.
tallbloke (07:39:45) :
Uh Huh. Small perhaps, but non-zero. So, not pseudo-science at all.
The pseudo-science comes in with precisely that argument. The gravitational effect on the Earth of a planet orbiting a star in a galaxy 10 billion light years away is also not zero, but believing that it will have any measurable effect is pseudo-science.
Why does the Sun’s equator rotate faster than the polar latitudes?
In terms a six year old can understand please.
The current understanding of this can be found in section 4.3 of http://solarphysics.livingreviews.org/Articles/lrsp-2005-1/
I quote the first few lines [where I have replaced the equations by ‘…’]
“The angular momentum per unit mass is defined as … where … is the angular velocity of the rotating coordinate system and … is the moment arm, … . An evolution equation for … may be derived from the zonal component of the momentum equation, averaged over longitude, and the result may be written as … The right-hand-side includes contributions from the meridional circulation, Reynolds stress, Maxwell stress, mean magnetic fields, and viscous diffusion. Complete expressions for each of these flux terms are given in Appendix A.4. The first term represents the advection of angular momentum by the mean meridional circulation, having the form … . The uniform rotation component of this, … , represents the Coriolis force which redirects meridional flows into zonal flows.” etc.
Now, this is not good enough for a six-year old [or for you or Vuk], but each term used can be explained in simpler terms and those, in turn, by yet simpler terms until it is simple enough. All that is required is immense patience on the part of both teacher and six-year old [the latter is the hard part].
Now, I don’t think you really meant what you asked for. If you did, I’ll be glad to educate you on angular momentum, Reynolds stresses, magnetic fields, etc [I have tried in the past – with perhaps minimal success …].
tallbloke (07:39:45) :
Why does the Sun’s equator rotate faster than the polar latitudes? In terms a six year old can understand please.
There are two possibilities, either you were being facetious [the most likely], or you genuinely want to know. If the latter this may be a bit OT, but we can hope that the moderators will et it pass. As I said, “The current understanding of this can be found in section 4.3 of http://solarphysics.livingreviews.org/Articles/lrsp-2005-1/ ”
Study that carefully and when you are stumped the first time, we can discuss that point, etc.
Leif Svalgaard (07:50:59) :
“Light is bent by gravity, so why not much heavier and slower particles in the solar wind?”
one might entertain the idea that Jupiter, for example, would act as a gravitational lens and concentrate the solar wind onto the Sun-Jupiter line. That might give rise to a point of enhanced density at the Heliopause
I might elaborate on this a bit. A point is probably not correct as there is no guarantee that the focus will be at the Heliopause. So, perhaps, we’ll get an Einstein Ring [as the gravitational field of Jupiter is not lumpy], so a good pseudo-scientist would say “Aha, the Ribbon is a gravitational Einstein Ring due to Jupiter”. Now there should then also be similar rings due to Saturn, Uranus, and Neptune [the other planets are probably too small to create enough lensing]. So we confidently predict such Rings and, there is more: predict that they will move as the planets move.
tallbloke (07:27:31) :
asked by Vuk to put up a thread for this topic on my blog
Now, I really meant what I said about a step-by-step explanation that he could understand. Apparently he was not interested.