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At System’s Edge: The IBEX ‘Ribbon’

Studying the heliosphere and its interactions with the interstellar medium isn’t easy, which is one among many reasons we follow the fortunes of the Voyager probes with such continuing fascination. They’re pushing up against the boundary between the Sun’s local ‘bubble’ and deep space beyond, where charged particles from the solar wind are no longer a factor and the deeper rhythms of the galaxy take hold. Now our other probe of this exotic region is back in the news in a new paper. IBEX (the Interstellar Boundary Explorer) is telling us much about how our system interacts with the interstellar medium and the effects of the galactic magnetic field upon the heliosphere.

IBEX has provoked much discussion in these pages — I was amazed to see I had written fully thirteen articles on the mission in the last six years, going back to pre-launch speculations. The mission caught my eye because it was the first ever sent with the express purpose of studying the outer edges of the Solar System. The Voyagers, obviously, are powerful tools, but exploring the heliopause was not their primary mission, nor are they optimized for this kind of work. What IBEX gives us will tell us much about the strength of the interactions in the heliosheath at system’s edge.

Recall that despite its target, the IBEX spacecraft itself orbits the Earth (with an apogee of 322,000 kilometers and a perigee of 16,000 kilometers), studying the heliosphere’s boundary by examining energetic neutral particles (ENAs) that help to define it. These ENAs are swept up and scattered by the solar wind in the boundary between the edge of the heliosphere and interstellar space. IBEX has created maps based upon those ENAs that go on to pass near the Earth, telling us much about the structure of the heliosphere, and discovering that the ENA emissions do not resemble what previous models had predicted.

IBEX principal investigator David J. McComas (SwRI) commented on the most newsworthy of the IBEX results back in 2009:

“The IBEX results are truly remarkable, with emissions not resembling any of the current theories or models of this never-before-seen region. We expected to see small, gradual spatial variations at the interstellar boundary, some ten billion miles away. However, IBEX is showing us a very narrow ribbon that is two to three times brighter than anything else in the sky.”

Image: This graphic illustrates one possible explanation for the bright ribbon of emission seen in the IBEX map. The galactic magnetic field shapes the heliosphere as it drapes over it. The ribbon appears to trace the area where the magnetic field is most parallel to the surface of the heliosphere (the heliopause). Credit: SwRI.

The ribbon feature was an unanticipated finding, one that required the development of a method to separate the ribbon from background emissions to obtain clearer resolution. In the new paper, Nathan Schwadron (University of New Hampshire) describes the process. Schwadron says that isolating and separating this ribbon of energy from the IBEX data was ‘like pulling the drapes from our window to discover the landscape at the edge of the solar system.’

One useful result of this work is that by learning more about the physical properties of the heliosphere, we will have a better idea how galactic cosmic rays operate both outside and inside the heliosphere, with obvious implications for planetary radiation environments not only in our system but in those around other stars. This is a murky area, and while we know that the most powerful galactic cosmic rays can penetrate the Earth’s magnetic fields and atmosphere, we have much to learn about how the heliosphere protects the Solar System from less powerful background cosmic rays.

The maps IBEX is making are probing unexplored terrain and, as the energy ribbon shows, contain surprising features.

Schwadron again:

“There are many theories about how the ribbon is created, and we don’t understand exactly what we’re seeing but it seems to be telling us something about how the local galactic magnetic field interacts with the heliosphere. This galactic magnetic field may be a missing key to understanding how the heliosphere protects the solar system from galactic cosmic rays.”

Other features of interest from the IBEX data are a ‘tail’ of emissions at the boundary — one that seems to be deflected in the direction of the galactic magnetic field — and the ‘nose’ of the heliosphere, which Schwadron likens to the “bow wave in front of a ship, which shows us how our motion through the galaxy compresses and deflects the material of the local galactic medium around our heliosphere.” But it’s worth noting that what IBEX has shown us so far differs greatly from what mission planners had expected. The crucial role of the galactic magnetic field now becomes apparent as our planetary system interacts with the galaxy.

The paper is Schwadron et al., “Separation of the Interstellar Boundary Explorer Ribbon from Globally Distributed Energetic Neutral Atom Flux,” Astrophysical Journal 731 (10 April 2011), p. 56 (abstract).


Comments on this entry are closed.

  • Alex Tolley April 4, 2011, 10:14

    Does this finding add any information to the possible 62 million year extinction rate cycle as proposed by Muller?

  • ljk April 4, 2011, 14:47

    How will these new findings affect interstellar vessels moving through those regions of space? Will they be a detriment or danger or will a way be found to make traveling to other star systems easier by their existence?

  • Rob Henry April 4, 2011, 19:57

    I was thinking along the lines of Alex Tolley, and recalled a disaster novel by Fred Hoyle; The Inferno. In it our galaxy had just become a quasar, and most scientists on Earth remained adamant that our galaxies magnetic field would protect us from the worst parts of its charged ion radiation. The hero however, pointed that the energy of such an explosion was more than sufficient than that required to completely disrupt this protective shield, and so we could have no confidence in what would happen next.

    This whole story relied on two ‘facts’. Firstly that the various celestial magnetic fields surrounding us provide far more protection than the casual observer realises, and second that the nature of these fields is hard for us to model sufficiently well to forecast their behaviour accurately. I always hoped that Hoyle was using writers licence there but, with articles like this one, I am starting to feel that he wasn’t.

  • John Freeman April 4, 2011, 20:08

    Its intuiging that the ribbon runs perpendicular to the direction of the galactic magnetic field…. Oh for a targeted mission that could get that far out in less than decades….

  • Michael Kirsch April 17, 2011, 11:44

    Every time we send up a new satellite, we discover that what we thought we knew was wrong. The fact that the galactic magnetic field has a highly structured relation to the heliosphere, really just goes to show how little we know about the structure of the heliosphere. This also relates to recent findings that the magnetic fields of galaxies have played a much bigger role in the formation of galaxies, and that galactic magnetic fields can’t be explained by the dynamo theory.

    Alex Tolley is right on the money, and I wonder more what he’s thinking on the implications this has 62 myr fossil biodiversity cycle. Mellot’s 62 myr cycle of our solar system bobbing through the galactic plane is the most compelling explanation for Muller’s fossil cycle and this finding by Schwadron provides a clue that the structure of the galactic magnetic field that we are interacting with at different parts of the 62myr cycle and 140 myr cycles through our galaxy could provide insight for fossil biodiversity.

  • Michael Kirsch April 17, 2011, 13:38

    John’s wish is not in vain, and is a correctly placed expectation. In the 1950’s, space agencies were working on nuclear rockets, and helium 3 fusion rockets(which we could build via some moon mining), could get us to mars in a week!

    Correction above. I meant to write: “this has –for the–62 myr…”