Io’s footprint on Jupiter takes the lead

By Phil Plait | March 17, 2008 10:29 am

Jupiter’s magnetic field is enormous, which is fitting for the King of the Planets. It is far stronger and larger than Earth’s, and, not surprisingly, far more complex. Still, some parts of it are just like home: Jupiter has aurorae.

This has been known for years; the interaction of Jupiter’s magnetic field with its atmosphere creates the northern and southern lights in much the same way that it happens on Earth. But Jupiter has something we don’t: a volcanically active moon.

Io spews sulfur from a series of volcanoes on its surface. The sulfur atoms go up into space, get ionized, and interact with Jupiter’s magnetic field as well. Waves of electromagnetic energy are created, and these travel along the magnetic field lines, slamming into Jupiter’s atmosphere. Io is, in a way, connected to Jupiter, and you can see this connection, literally, as a bright spot of ultraviolet light on Jupiter.

Like on Earth, this happens in both of Jupiter’s hemispheres, producing a Jovian equivalent of northern and southern lights. As Jupiter rotates, the connection spot leaves a glowing trail that fades with time, so it looks like a spiral-shaped comet on the top of Jupiter’s atmosphere. By studying that spot and trail, scientists can learn about the planet, the moon, the magnetic field, and their interaction… and get a surprise or two in the process, too. A new paper just released shows that something unexpected has turned up in Hubble images of Io’s UV footprint: a leading spot, ahead of the main bright spot.

That’s weird! The bright spot is the place where Io is connected magnetically to Jupiter, so you simply don’t expect to see a spot ahead of that one. Yet there it is. The scientists noticed something else, too: when there is a leading spot in Io’s footprint in one hemisphere of Jupiter, there are multiple spots in the other hemisphere. This led to think that there is more going on here than previously thought. Evidently, there is some sort of magnetic connection between the north and south pole of Jupiter, directly from Io’s northern footprint to its southern one. Something like what happens in a CRT, beams of electrons are being guided from one pole of Jupiter to the other. Compared to the main connection to Io, the connecting beam is weak, so the leading spot is dim, but it’s there.

Here’s what they think is happening: Io blasts sulfur into space. This forms a torus, a doughnut-shaped region of plasma surrounding Jupiter (yellow-green in the illustration above). The magnetic field of the giant planet ionizes the sulfur. As Jupiter’s magnetic field whips past Io, it connects with the moon, and waves of energy flow from Io to Jupiter, creating the bright footprint spot and trail (not shown, but the stream is in blue). The spot is connected to its opposite-hemisphere counterpart by the electron beam (shown in red), and that’s what creates the leading, fainter spot.

This is all very complicated, of course. Jupiter makes a fiercely complex system, and studying it can be very difficult. Observations like this can really mix things up, but the good news is that new data always point us in the right direction, toward truth. And the better news is that in September astronauts will attempt to fix Hubble’s premier ultraviolet camera, called STIS (it’s the camera I worked on in Days Gone By). When it’s fixed, we’ll be able to get higher-resolution images that can see fainter spots, so the picture of Jupiter’s connection with Io will literally become clearer.

Comments (21)

Links to this Post

  1. paper moon | March 18, 2008
  1. Moose

    So, you’re saying that if we spacewalk in Jupiter’s orbit near Io, and we remove our helmet, space will stink for the however many seconds it takes us to die from exposure, asphyxiation, and the massive dose of radiation we’ll take?

    Cool.

  2. Donnie B.

    So does this magnetic interaction steal angular momentum from Io’s orbit? Is it destined to spiral down until it reaches the Roche limit and breaks up into a new ring?

  3. occam's comic

    Well, well, well, BA is comming very close to saying there is Electricity in Space and that it acutally does stuff. (Moving steams of charged particles is the definition of an electric current.)

    But I don’t think that it is the magnetic feild per say that is ionizing the sulfur, but the interaction with the plasma in the magnetic feild that is ionizing the sulfur.

  4. occam’s comic, please. The Electric Universe theory is totally wrong, and one way it’s wrong is that its devotees love to say that astronomers won’t acknowledge that plasmas are important. That’s a lie. Of course we understand about plasmas. We also understand that gravity is important, and on a large scale is generally more important. We also understand that large solid objects tend to be electrically neutral, an aspect EUers cannot seem to grasp.

  5. Donnie B, as I recall, the energy is ‘stolen’ from Jupiter’s rotation, which is what moves the field round. Since angular momentum is conserved I think that must mean that Io moves outwards (and presumably Europa and Ganymede move out, too, to maintain the resonance).

    However, there’s also the effect of the tides that Io raises in Jupiter’s atmosphere (also pushing Io out), and the effect of the tides raised by Jupiter in Io itself (as I recall, pulling Io in), and I’m not sure what the aggregate effect is.

  6. occam's comic

    OK BA, you are willing to say plasma and electrical phenomenon are important in astronomy, could you do a post(s) clarifying what phenomenon you think are plasma related and what are not? Also what evidence leads you to think that way?

    Now, the Electric Universe folks may be totally wrong, or right on some things and wrong on others. But they are presenting a theory that is falsifiable and I am happy to admit a theory is wrong when the evidence shows that is wrong.

    Some potential topics claimed to be explained as plasma phenomenon by the Electric Universe Theory:
    Northern lights
    Solar wind
    Suns Corona
    Suns power source
    X-Ray emissions from comets
    Structure of nebulas
    Heleopause
    Structure of the Galaxies
    “Volcanoes” on Io
    Structure of the Universe

    Now I know that I am asking a lot, but maybe semi regular posts could show us non professional astronomers why some explanations are wrong.

    (I have always learned more from my errors than from my successes.)

  7. andy

    Sun’s power source: nuclear fusion has an awful lot of evidence going for it: especially now there’s evidence that the neutrino weak eigenstates are not the same as the neutrino mass eigenstates (thus neutrino oscillations occur, which solves the solar neutrino problem). In fact, it is not entirely clear under plasma cosmology why the Sun should have had a fairly stable output for the past billions of years – if it drifted with respect to the cosmic plasma currents postulated under electric universe theory, the output of the Sun should have changed dramatically, thus making life on Earth impossible.

    Volcanoes on Io: energy production by tidal flexing is adequate to explain this activity, no need to invoke plasma physics. Besides, why isn’t Earth’s geology powered by plasma interactions, if all the rest of the geology in the solar system is?

    Structure of galaxies: I don’t know how the electric universe proponents get around it, but gravitational lensing theory seems to work pretty well.

    Structure of the universe: actually a failing of the electric universe: electric universe predicts large scale structure, however observations show that at scales of ~100 Mpc the universe is pretty isotropic.

    However, northern lights, solar wind, the corona and the heliopause are indeed magnetohydrodynamic phenomena. This is no problem in standard cosmology. On the other hand, the electric universe goes too far in ascribing everything to plasma phenomena.

  8. Of course there’s electricity in space. How else would they power an iPod on the shuttle?
    If Io is constantly blasting sulfur into space, does that mean the moon is shrinking?

  9. occam's comic

    Andy, I agree the electric universe folks go too far in ascribing everything to plasma phenomena.

    Structure of the galaxies, I agree the degree of gravitational lensing matches up to missing mass (dark matter/ dark energy) theories and not to the electric universe theory.

    Why do I think that “Volcanos” on Io might be caused by electrical currents, to quote BA
    “Evidently, there is some sort of magnetic connection between the north and south pole of Jupiter, directly from Io’s northern footprint to its southern one. Something like what happens in a CRT, beams of electrons are being guided from one pole of Jupiter to the other”

    Now this current may not be strong enough to “electro machine” material off the surface of Io but I think worth testing to see if it does or does not explain what is going on.

    As for rest of the geology of the solar system my view is that some of the features in some places might be caused by plasma. I think the Electric Universe guys go too far in see plasma responsible for everything (kind of like when you first use a hammer all the world becomes a nail ;-)

    Power source for the sun, if the neutrino problem has truly been solved that resolves many problems. Oh well, it was fun thinking about fusion occurring in the sun’s corona rather than inside the sun and the parallels to Bussard’s fusion work.

    Andy, you did not mention the structure of nebulas, could this be an area that needs an explanation that includes magnetohydrodynamic phenomena, because it hard for me to see how gravity and simple fluid flow could create what we see.

  10. LeeTheAgent

    Did you ever read 2010? Clarke wrote some very imaginative descriptions of the interaction of Io and Jupiter, very vivid and beautiful. If you read those descriptions, what, as a modern day astronomer, do you think of them? Reading this blog really reminded me of that part of the book.

  11. Captain Swoop

    [quote]Now, the Electric Universe folks may be totally wrong, or right on some things and wrong on others. But they are presenting a theory that is falsifiable and I am happy to admit a theory is wrong when the evidence shows that is wrong.[/quote]

    Where is the Theory they have presented? All we ever see are a few suppositions and claims on web sites. Or do you mean ‘Theory’ in some non scientific meaning of the word?

  12. Come on, folks! It’s THE SCHWARTZ! Don’t they teach kids anything these days?

  13. OneHotJupiter

    Those photographs are amazing , FSM bless the Hubble Repair mission!

  14. Tom Marking

    “The magnetic field of the giant planet ionizes the sulfur.”

    Huh? I’d like the mechanism for this explained a little bit better. Isn’t it a whole lot more probable that the protons and electrons buzzing around in Jupiter’s magnetic field slam into these sodium atoms and knock electrons off of them. How could the magnetic field directly ionize the sodium atoms?

    Also, the green torus of sodium ions in the image makes no sense to me. Once these sodium atoms are ionized they will spiral around Jupiter’s magnetic field lines and go back and forth between the north Jovian magnetic pole (or directly above it) and the south Jovian magnetic pole until they interact with the Jovian atmosphere and get absorbed. This is similar to how protons and electrons interract with earth’s magnetosphere to generate the aurora borealis. The main point is that the sodium ions will not be constrained to a toroidal region since there is nothing keeping them in that region of space. So the whole picture looks wrong to me.

  15. Torbjörn Larsson, OM

    “electro machine” material off the surface

    That is bona fide sputtering, and is analogous to solar wind sputtering of atmospheres.

    But the volcanoes on Io is volcanoes.

    Btw, the sputter rate of electron beams is ridiculously low, as electrons have 1/2000th of hydrogen mass. Instead they vaporize material due to induced heat.

  16. Torbjörn Larsson, OM

    I should qualify the electron beam description, as in most cases the acceleration mechanism puts as much energy into the current as a comparable ion current. But sputtering, even with multiple knock-on collision cascades, is very dependent on mass matching between sputtering particle and target particles.

    Thus, physical sputtering with electron sucks.

  17. B. Bonfond

    Thank you very much to BA to summarize our paper in such an exciting manner. It’s so motivating to see that our work has some echo on the web.

    I would like to answer to one or two questions raised in the comments.
    -First of all, volcanism at Io is pretty well explained by the effect of tidal forces without the need of any electric current. That fact is that Io is very close to a giant planet and that it orbits quasi-exactly twice faster than Europa and four times faster that Ganymede. This resonance perturbs Io’s orbit and huge tidal forces distort Io, which generates heat and thus volcanism.

    -What ionizes the SO2 neutral gas is both UV radiation (from the sun) and electron impact.

    -The confinement of the torus particles is an observational fact (Earth observatories and various probes passing by pictured and measured it). Ions are frozen on their field line and can only spiral along it. Since they rotate around Jupiter as fast as the magnetic field (10h instead of 42h for Io), they experience strong centrifugal forces that confine them as far as possible from Jupiter, i.e. in the plasma torus.

  18. Tom Marking

    “-The confinement of the torus particles is an observational fact (Earth observatories and various probes passing by pictured and measured it). Ions are frozen on their field line and can only spiral along it. Since they rotate around Jupiter as fast as the magnetic field (10h instead of 42h for Io), they experience strong centrifugal forces that confine them as far as possible from Jupiter, i.e. in the plasma torus.”

    “and these travel along the magnetic field lines, slamming into Jupiter’s atmosphere.”

    First of all, I misspoke. I said sodium ion when I meant to say sulfur ion. Now if you consider the two paragraphs above you can see that they are contradictions. If the ions are confined to the torus far away from Jupiter then they obviously cannot slam into the Jovian atmosphere in the polar regions. It’s got to be one or the other. The magnetic field lines do not run parallel to the green torus in the picture but rather perpendicular to it (roughly north-south but arcing around to connect with both the Jovian north magnetic pole and the Jovian south magnetic pole). Charged particles follow the magnetic field lines which would take them in and out of the torus.

    The torus might well be made up of neutral sulfur atoms expelled from Io which have not yet been ionized. They would tend to follow the same orbit as Io and would essentially be tiny moons of Jupiter following along the same orbit. Once they become ionized they follow the magnetic field lines which take them out of the torus. But of course, this was never explained in the initial post although it’s a reasonable conclusion. And the initial post had the erroneous statement that Jupiter’s magnetic field directly caused the ionization to begin with.

  19. Torbjörn Larsson, OM

    @ Tom:

    Charged particles follow the magnetic field lines which would take them in and out of the torus.

    Remember our own Van Allen belts, where AFAIK particles are confined from the poles by magnetic mirroring. (I.e. when the field lines converge they force gyrating particles to revert.)

    I assume the post was short on details as the physics seems to be well established. The flux tube is a magnetic flux tube similar to the ones on the suns surface. This is what confines the electric current along the tube.

    You should not assume that plasma currents necessarily is due to individual ions, and consequently that the density of a plasma must reflect the density of a current through parts of it. In fact, I note that these particular currents are known to have particles typically coupled by way of fields I wouldn’t know that, because I haven’t studied these specific phenomena. But it is a recurring phenomena.

  20. brant

    Since when does a magnetic field ionize anything?

    That would be the job of the electric field accelerating the particles…..

    And since the flux tubes are flows of charged particles, that constitutes a current flow.

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