Watching the birth of a comet magnetosphere

Based on the press release of the Swedish Institute of Space Physics summarising the results of the Rosetta Plasma Consortium’s (RPC) Ion Composition Analyser (ICA) that are presented in the journal Science today, and on follow-up discussion with Hans Nilsson, RPC-ICA principal investigator.

The RPC-ICA instrument onboard Rosetta has been watching the early stages of how a magnetosphere forms around Comet 67P Churyumov-Gerasimenko as it moves closer to the Sun along its orbit and begins to interact with the solar wind.

How a comet grows a magnetosphere 1. The comet approaches the Sun 2. Water molecules sublimate from the comet as it thaws 3. The water molecules are ionised by ultraviolet light from the Sun 4. Newborn ions are accelerated by the solar wind electric field and are detected by the RPC-ICA instrument 5. The solar wind accelerates the water ions in one direction, but is itself deflected in the opposite direction Credits: ESA/Rosetta/RPC-ICA

How a comet grows a magnetosphere
1. The comet approaches the Sun
2. Water molecules sublimate from the comet as it thaws
3. The water molecules are ionised by ultraviolet light from the Sun
4. Newborn ions are accelerated by the solar wind electric field and are detected by the RPC-ICA instrument
5. The solar wind accelerates the water ions in one direction, but is itself deflected in the opposite direction
Credits: ESA/Rosetta/RPC-ICA

As the comet gets warmer, volatile substances, mainly water, evaporate from the surface and form an atmosphere around the comet. The Sun's ultraviolet radiation and collisions with the solar wind ionizes some of the comet's atmosphere. The newly formed ions are affected by the solar wind electric and magnetic fields and can be accelerated to high speeds. When the comet gets close enough to the Sun, its atmosphere becomes so dense and ionized that it becomes electrically conductive. When this happens, the atmosphere starts to resist the solar wind and a comet's magnetosphere is born – a region surrounding the comet that is shielded from the solar wind.

"The comet environment is a laboratory for scientists; we can see what happens when the solar wind streams through an atmosphere," says Associate Professor Hans Nilsson at the Swedish Institute of Space Physics (IRF) in Kiruna. Hans Nilsson is responsible for the instrument Ion Composition Analyser, ICA, developed and built in Kiruna. The instrument measures positively charged ions and is one of five instruments in the Rosetta Plasma Consortium.

Hans explained that studying the interaction of the solar wind with a comet's atmosphere in this way could shed light on how the solar wind interacted with the planets during their early formation. "In the young Solar System, the planet’s upper atmospheres were strongly heated and extended far into space. The solar wind should have streamed through the outer part of these extended atmospheres in a way that resembles its passage through the comet atmosphere for this low activity stage," he explains.

At 67P/C-G, Rosetta’s RPC-ICA instrument detected low velocity water ions in data collected on 7 August 2014, one day after arriving at the comet at a distance of 100 km.

"It was an unambiguous signature of the comet, a clear detection of ions from the comet's atmosphere," confirmed Hans.

Rosetta is a unique space mission. Previous spacecraft that have studied comets have rushed past them at a great distance and at speeds of tens of kilometres per second. At the time of these previous spacecraft-comet encounters, the comet magnetosphere had been fully developed. By comparison, Rosetta is currently orbiting around 67P/C-G at a distance of just a few tens of kilometres, and at low speed. Importantly, the mission arrived at the comet in time to watch the very early stages of the magnetosphere formation.

“For the first time, we can see what happens before the comet atmosphere resists the solar wind," says Hans. "We discovered that the comet atmosphere affects the solar wind more than we thought it would at this early stage. We are also surprised how much structure we see in our data – the comet atmosphere appears to be very unevenly distributed around the nucleus.

"We are still in the early stages of analysing and modelling our data, but perhaps the energy transfer from the solar wind to the atmosphere is less efficient in removing an atmosphere than we originally thought.
As the comet moves closer to the Sun along its orbit, Hans and his colleagues will see the transition from this early phase to the growth of a well established comet magnetosphere.

"That transition is likely the most exciting part," he says. "It can happen any day now. Every morning we keep looking at the new data which have just arrived. What will we find today?"

"Birth of a comet magnetosphere: a spring of water ions," by Hans Nilsson et al., is published in 23 January issue of Science

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Editor's note: On previous blog entries, some of you have been discussing about the formation of the comet's bow shock – a question I put to Hans, who says:

"We do not know for sure at what distance the bow shock is formed. At the distance we are right now [30 km from the comet] we can see that the solar wind is not shocked, and it does still permeate the comet atmosphere down to where Rosetta is located. So we do know that the magnetosphere has not formed yet, and we would at least indirectly see when it is formed. According to the models, the bow shock should form quite far away, so we would need rather large excursions away from the comet to observe it in situ."

Comments

67 Comments

  • Prof Harvey Rutt says:

    Many thanks for answering the question!

    • originalJohn says:

      Ah, Harvey, you are happy now , because you have been informed that the mere presence of ionised material will signal the existence of a magnetosphere, a magnetic field, in association with this comet nucleus, and you see this as a vindication of something. In which case I am sorry to disappoint you Harvey but this is nonsense and I strongly advise you to dissociate yourself from it. It is not a magnetosphere if it is a magnetic field generated by a remote, isolated current flow because of a potential at some point in the plasma of the coma. I can also assure you that it is not a requirement for the plasma to become "dense and ionised" to become electrically conductive. It would be electrically conductive and display all the properties of plasma if it was only 1% ionised and at virtually any density.
      So, as soon as it is established with certainty that this comet nucleus has its own magnetosphere it will be solid, cast iron, indisputable proof that there is an electric current not only flowing to it but through it. So you are right, it would be a vindication but not of what you thought. And it would confirm once and for all that we are dealing with an electric comet. And this of course could be taken as more than a subtle hint that you, Harvey, are living in an electric universe.

      • Gerald says:

        The solar wind accelerates the water ions (forming in the coma from sublimated ice) in some direction. Only a small fraction of this will eventually hit the nucleus, since the coma is much larger than the nucleus.

        The 20 keV must be some misunderstanding, since keV is a unit often used for energies of individual elementary particles, atoms, molecules, or ions; it's not an electric potential. But I don't know which context the number comes from.
        I thought, the electric potential of Rosetta is about -6V.
        That way there is a chance to collect ions in the sub 10 eV range.

        • Gerald says:

          Sorry originaljohn, this post has been intended as a reply to Robin Sherman below.

  • daposter says:

    very cool indeed
    now that the paper is written, maybe there will be a release of more than just the condensation of the paper...
    just to see the dynamics and how this all changes over time from the first measurements to the current ones....

  • daposter says:

    are there any data you can add on the particle density and velocity of the solar wind at that distance?

    • Graham Hall says:

      The papers are online and freely downloadable from the science website.

  • bretagne22 says:

    Is the word "magnetosphere" the right one ? Generally a magnetosphere around a celestial body implies that this body has a magnetic field.

    • Gerald says:

      Yes, they refer to the magnetic aspect for the deflection of part of the solar wind.

    • Ross says:

      The comet is a moving, rotating charged body. It has a magnetic field, which focuses the jets to persist in the neck region.

  • Bill Harris says:

    The new ions are accelerated by the solar wind electric field, so the effect appears to be electrostatic. But, OTOH, if you move a conductor through a magnetic field, it will move electrons in the conductor (ie, voltage, and if you apply a voltage to the conductor, the electrons will move, creating a magnetic field. And a plasma is a conductor It's a blurry line.

    --Bill

    • originalJohn says:

      What potential, Bill, do you attribute the cause of the solar wind electric field to ?
      And, beyond dispute, a flow of current (not only electrons, any ions) in a conductor generates a magnetic field, or a magnetic field interacting with a conductor generates a flow of current, establishing a potential. But whereas a potential and therefore a current flow can occur in many ways, a magnetic field can only be generated in one way, by the flow of an electric current. A magnetic field is therefore a specific indicator of current flow.
      A magnetosphere is the magnetic field of body and that field originates at the body, so is envisaged as connected to it. The electric current necessary for the generation of that magnetic field must therefore also flow through the body.
      The body in the case we are referring to is the comet nucleus with its own magnetic field, or magnetosphere, should such a field be discovered, generated by the required flow of current through it. The current would be carried to the body in the surrounding plasma, in self induced filamentary form (each filament incidentally, with its own, self induced magnetic field).
      Crystal clear isn't it?

      We should remember, by the way, that there is a limited class of materials, called ferromagnetic (or the very much weaker paramagnetic) materials that are either naturally magnetic or in which magnetism (and therefore a magnetic field) can be induced without the necessity for continuous current flow. Plasma is not one of that class. Should the nucleus turn out to consist of one of those natural materials or contain a significant amount of it then it would be an alternative source of a magnetosphere, which could be the sole source or superimposed on an electromagnetic source. If the possibility of the presence of such a material in the nucleus was eliminated, then electromagnetism would be the sole possible source.

      • Gerald says:

        "The electric current necessary for the generation of that magnetic field must therefore also flow through the body."
        That's wrong. Take a piece of paper and place it between a horseshoe magnet. This works with a ferromagnet as well as with an electromagnet.
        There is no need for an electric current flow through the piece of paper, neither through the comet nucleus.
        The magnet can be formed entirey in the surrounding plasma.

        • originalJohn says:

          In which case it is not a magnetosphere. It is a random magnetic field.
          I don't see the point of the horseshoe magnet analogy. An electromagnet conductor induces a magnetic field centered on and surrounding the conductor form in which the current is flowing. Placing a ferromagnetic material in the field simply intensifies the field. The current therefore must flow though the conductor, the nucleus in the case in question. The field, if a magnetosphere, passes through the nucleus in the same way the Earth's field is depicted as entering at the south pole and emerging at the north (magnetic) pole, or the bar in the case of a bar magnet field. And the Earth's field (magnetosphere) is detectable at sea level all over the surface of the planet, by compass needles. If a current passes through an approximately spherical body it will induce a dipolar magnetic field centered on that body.

          • Gerald says:

            The point is, that you're confusing cause and effect.
            An effect doesn't prove the cause, since several causes can result in the same effect.
            Here, a current surrounding an insulator can cause a magnetic field within the insulator. No current is needed within the insulator.
            In the case of the cometary magnetic field, the comet is an insulator, and the surrounding plasma is a conductor.
            Silicate dust, water ice, carbon dioxide ice are very poor conductors in contrast to plasma. So just forget the negligible currents withing the comet, and look at the almost perfect conductor we know of, the surrounding plasma.

  • TomsThumbs says:

    Only one problem: There is no water (or ice) on the comet, soooo sublimation is out. Methinks its the other way around and the water ions detected are hydroxyls created as a byproduct of electrical interaction with the solar wind.

    • Gerald says:

      There is no unique detection of water ice in the top-most few micrometers; that's not really surprising in contact with vacuum, since water ice sublimates rapidly in the vacuum at temperatures above about 100 Kelvin; surface temperatures are now much higher at sun-exposed locations, and have been even higher through the previous perihelion.
      The water ice, as well as ices of carbon dioxide and carbon monoxide are below the top-most layer, mixed with dust, or if the silicate, sulfide and organic material is more spongy, in pores.

      Btw.: How could carbon dioxide gas form from silicate or iron with protons from the solar wind?

    • originalJohn says:

      A magnetic field "within" the insulator.? You think the nucleus is behaving as an insulator, I think it is behaving as a conductor and the conductivity is essential to generate the field.. Do you think the planet Earth is an insulator? In which case what is the relationship between the Earth and its magnetosphere. The magnetosphere forms because the Earth is a conductor.
      If the comet nucleus is an insulator and the surrounding plasma is a conductor and has a magnetic field that field has no connection with the nucleus, The simple cause and effect is that the flow of current in a body generates a magnetic field of that body.

      • Prof Harvey Rutt says:

        You 'think it is behaving as a conductor'?
        It is one, or it isn't one.
        Rock and ice, whichever, are rather good insulators.
        The earth has a darn great (conducting) nickel-iron core; and an observed magnetic field at the surface typically in the tens of uT.
        No shred of evidence for such a core in a comet, vast evidence against, and directly observed fields are just the interplanetary field distorted by the comet's plasma, in the nT region.

      • Gerald says:

        Yes, of course the comet body is an insulator. Did you ever try to conduct a current through rock or ice, particular in the presence of a conductor (here the surrounding solar wind plasma and ionized gas, but you may take copper wire, compare the currents with and without the surrounding conductor)?
        And Earth's magnetic field is well-known to be mostly generated by its rotating iron-nickel core.
        It's modified by solar wind interaction.
        Earth's crust is no good conductor, most rock is better called an insulator. Salty water of the oceans is a conductor, but with quite some resistance.
        If there would be a considerable electric current in the oceans, they would heat up by Joule heating (http://en.wikipedia.org/wiki/Joule_heating), and they would be electrolyzed into hydrogen and oxygen. This effect isn't observed.
        Hence assuming significant electric currents through the Earth is pure nonsense.

        The magnetic field isn't constrained to the magnet, or to the conductor in case of an electromagnet. It can easily penetrate nearby insulators.
        Hence it can well be caused by the conductive plasma and penetrate the electrically insulating comet nucleus.

        • Gerald says:

          More explicite: The plasma is the body with the current causing the magnetic field of the magnetosphere, not the nucleus.
          The Earth analog doesn't hold, since the much stronger magnetic field of the Earth is mostly caused by Earth's metallic and partially liquid core.
          Details of geomagnetism in Wikipedia:
          http://en.wikipedia.org/wiki/Earth%27s_magnetic_field#Physical_origin

        • originalJohn says:

          Electrons are gathered from the surface of rock bodies over large distances to points of lightning discharge. On a body the size of a comet this effect could occur pole to pole.

          • Gerald says:

            If you would argue by rapid charge separation by emitted dust in jets, I could consider a build-up of an electric field at the source regions of jets. This might work particularly well after an insulating atmosphere is established. So if you like to look for discharges I'd consider this settings as most promising.

            For the pole-to-pole scenario I don't see a convincing mechanism thus far. But since the comet is an insulator, different electric charging of some moderate level may be possible. But at some point the solar wind plasma will start to level out most of the potential difference.

  • Robin Sherman says:

    Hi depositor. There are some figures for proton and alpha particle fluxes in the Solar Wind in the supplementary material published with the report. There are details of how the collision cross sections with water molecules could be used to estimate the number of H2O+ ions that would be created.

    What I hadn't realised is that the ions the Solar Wind creates and those produced by ionising radiation are accelerated TOWARDS the comet by the energy of the Solar Wind and its electric field. So instead of the theory that the Solar Wind causes water loss from the comet and hence the coma, the opposite is true, the Solar Wind returns the water in the coma to the surface of the comet, at least water and other ions found in the coma.

    Others have said about Rosetta acquiring a charge or at least a potential, the figures here say that Rossetta has a negative Potential of about 20KeV. This actually helps them detect very slow moving, or cold ions, that it finds hard to detect, they are in effect accelerated enough to actually reach and show up on the detectors.

    This article does not discuss the interaction of the coma with the Sun's magnetic field, just the magnetic fields of the plasma making up the Solar Wind. That electromagnetic interaction was responsible we were told for the "singing comet". It would have been interesting to hear about progress of that investigation as well.

    • Ross says:

      The comet nucleus is a negatively charged body moving towards the sun, a positively charged entity. The increasing heat is unsubstantial in the mechanism which produces the coma and tail, evidenced by comet Lovejoy's recent survival through the corona with a disrupted tail. Sublimation is NOT the source of water to be photodissociated into ions. The hydrogen ions are accelerated toward the nucleus, reacting with the silicates to produce hydroxyls which accelerate away from the comet, forming water molecules. This leaves the Corbin skeletons to react with bombarding hydrogen to form hydrocarbons. Sublimation of unobservable ice is NOT required. Ockham's razor please!

      • Ross says:

        "This leaves the carbon..." not Corbin.

      • Gerald says:

        Silicates usually don't contain carbon. Where do those carbon skeletons come from?
        If it's silicates depleted of oxygen, there should form silicon-hydrogen species instead, like silane. They have not been detected.
        Instead carbon oxides have been detected, more abundant even than water, at some locations.

        If the nucleus would be negatively charged to allow for significant acceleration of solar protons, there should be a strong electrostatic field. This doesn't exist. The field strength has been about 1 V / km, hence very weak in terms of local particle acceleration ("The energy of the ion directly corresponds to the travel distance along the solar wind electric field, which is expected to be of the order of 1 V km^−1 or less.", http://www.sciencemag.org/content/347/6220/aaa0571.full).
        If the field would have been stronger, they would have measured much higher water ion energies.

        Don't apply Occam's razor on wrong assumptions.

        • Gerald says:

          Btw.: Even more obvious: If the comet nucleus would be charged strongly negatively, the positively charged water ions (O+, and H3O+) couldn't have left the nucleus.

          • Ross says:

            That's because you assume the water came from the nucleus. The hydroxyls are created first and would be abundant in the cathode jets. They then form water molecules away from the comet and may fall back towards the nucleus in rare circumstances (evidenced by Tempel 1). Hyperion was recently confirmed to be electrical during Cassini's fly-by; if a moon can sustain a charge then why couldn't a comet?

          • Gerald says:

            It could be charged by solar wind particles or uv radiation. But there isn't a planet with a strong magnetosphere near the comet to amplify such a charging, and the measured ion energies make a strong electric field unlikely.
            Even if we assume a negatively charged comet, for an instant, the proton flux would be much too low to explain the quantity of water ions measured.
            And we still have the silicon skeleton, which isn't observed. Nor is the sublimating carbon dioxide explained.
            Why doesn't our moon produce large amounts of water vapor, although electrostatically charged and closer to the Sun than 67P/C-G?
            There are simply much too many gaps and inconsistencies in the electric universe approach to be able to finally result in a conclusive explanation.

    • Gerald says:

      The 20 keV must be a misunderstanding, since that's an energy, not an electric potential; original full post unintentionally linked as a reply to originaljohn above.

      • Robin Sherman says:

        Sorry Gerald, my interpretation of the figures in the paper and the explanation that the potential of Rosetta was attracting low energy particles toward it, seems to have been confused. Trying to take in all that information at once I guess. It does make more sense if the 20 KeV referred to the energy of the ions it could attract.

        I am sure, as you say, many of the accelerated H2O+ ions would miss the nucleus, my intention was to indicate that they would be deflected back at an angle in the general direction of the comet, as one of the diagrams indicated, with the Solar Wind ions deflected at another different angle away from the comet. The point being, once the coma reaches a certain density, ions in the Solar Wind do not reach the comet. The suggestion of the team is that point should be somewhen about now.

        The use of the word "magnetosphere" did seem odd, since it is usually defined as being produced by an object's own magnetic field. I guess it is correct in the sense that the developing ionosphere in the comet's coma and the resulting magnetic fields, are generated by the object, since the coma is an integral part of the comet. The difference is only that the magnetic fields are created external to the solid part of the object, rather than internally in the case of planets like Earth, Jupiter and Saturn. Stars have magnetospheres and they contain only plasma so there is a generic meaning to the word which is being applied here, that is, "a magnetic field surrounding an object in space".

        • Gerald says:

          In the paper I've only found a 20 km/s number corresponding to 40 eV for "water" ions from the comet. Some solar wind ions may be at 20 keV. Maybe the upper bound of the instrument for ion energies?

          Great to see a ionosphere/magnetosphere emerge, for the first time! I'm sure, the next release of papers will be even more interesting, as the the comet gets more active.

  • masanori says:

    Glad to know that Rosetta arrived when the magnetosphere has not formed yet, so that we can see it happens. Hope we outside supporters are informed when it happens, instead of being informed some months later. From this blog or from RPC Twitter account or whatever we can find. Thank you and have fun!!

  • logan says:

    Very grateful to Emily for using his limited time with the investigators in conveying our wanders.

  • Prof Harvey Rutt says:

    Can I suggest
    http://www2.ku.edu/~kuspace/aeronomy/comet-tutorial.pdf
    As a little light reading. It's largely verbal, with little detailed maths to trouble you.
    Some might also find this helpful
    http://en.m.wikipedia.org/wiki/Electronvolt

    • THOMAS says:

      Hi Prof,

      You say:
      "Can I suggest
      http://www2.ku.edu/~kuspace/aeronomy/comet-tutorial.pdf
      As a little light reading. It's largely verbal, with little detailed maths to trouble you."

      Thanks first for your solicitude for those whom you consider to be numerically and/or conceptually challenged…

      The obvious problem with this "tutorial" is that the most recent paper among those cited dates from well over a decade ago, in 2003 (13 hits, with 0 hits for anything later).

      In their concluding paragraph ironically entitled "Future Prospects", the authors state:
      "Rosetta was scheduled for launch in January 2003, and arrival at comet 46P/Wirtanen was originally expected in 2011. Unfortunately, the Ariane launch vehicle is having difficulties and the launch has prudently been delayed. The most likely new comet target is comet Churyumov-Geramisenko."

      I’m sure you know that since then, we have learnt a lot more about the surprising properties and behaviour of comets, above all through the ‘Stardust’ and ‘Deep Imapact” missions….

      Methinks your ‘tutorial’ needs a little updating.

    • logan says:

      Thanks a lot Prof Harvey Rutt. Reading avidly. The tutorial easy. Jumping some formulas from the second 🙂

  • dave says:

    Its certainly interesting, Harvey, and it even quotes Alfen as a ref in the first paragraph.

    I guess then we have to wait for the measurements from the Rosetta team of which there should be many based on the equipment they have (as mentioned in the summary) before we make up our minds what is happening.

    I hope you're not crossing sides or we will need somebody else to do the debunking

    • Prof Harvey Rutt says:

      You jest! What on earth gave that impression?
      I have no problem with quoting Alfven, he did important work and did indeed suffer from the old school prejudices against novelty.
      The crazy distortions of that are another matter altogether.
      I'm kind of tired of 'doing the debunking'.
      Essentially we have three groups here.
      The 'conventional', the religiously committed 'EU' and the interested but not knowledgeable in detail, seeking information. The danger of course is that the last group will be mislead by the confident assertions of the 'EU' community, despite their complete disconnection from real physics.
      So I guess I'll chip in occasionally - but that third group have a problem, how do they decide which of the other two is right?

  • Prof Harvey Rutt says:

    Regarding the effects of solar wind on the surface of the comet which is illuminated, pre bow shock formation.
    Discussion tends to focus on proton illumination of basically silicate minerals; this itself may be inappropriate, as we seem to have a dark 'organic' layer on 67P which solar wind protons would probably not penetrate, it doesn't need to be very thick. Not present on the moon or asteroids of course.
    But, for the moment, thinking about broadly silicate rocks irradiated by protons at a few keV, broadly what might one expect?
    I've run some SRIM/TRIM simulations to support the speculation.
    Firstly, very low sputter yields, due to the low proton mass.
    Very little back scatter.
    More sputtering at high angles of incidence.
    All SRIM/TRIM confirmed.
    So sputtered off material is the substrate material, plus sputtered 'historically implanted' protons when equilibrium is reached. Naively, eventually one should reach an in=out equilibrium as the implanted concentration rises, but could take a very long time and other process can, probably do, prevent that equilibrium being reached.

    I would *not* expect sputtered OH to be common, possibly to exist at all, due to its low binding energy compared to projectile energies and 'escape' requirements. I can't find evidence on that either way., I could be wrong. SRIM/TRIM does not predict this detail.
    It should be in the SIMS literature I guess.

    So you might think the implanted protons will largely end up as OH captive in the thin surface layer. There has at times been support for this.
    But I found the fairly recent paper below, saying very clearly and convincingly, not so. Very nice SIMS, XPS and IR data. However I'm not clear what this means the ultimate fate of the protons is!

    Real physics based input welcome.

    (To be crystal clear, this whole mechanism is umpteen orders of magnitude too weak to explain the water emitted by comets in their active phase, and there is no credible mechanism to form neutral water molecules on the scale required by it.)

    http://onlinelibrary.wiley.com/doi/10.1029/JZ071i020p04855/abstract

    • Gerald says:

      Thanks a lot for investing that much of your precious time to provide an overview of basics of the comet - solar wind interaction!

      Here a 2014 LPSC paper about the fate of protons implanted into silicates:
      http://www.hou.usra.edu/meetings/lpsc2014/pdf/2004.pdf
      If I understand it correctly, the proton uses to end up as the H in SiOH for hydrogen-free silicates.
      A pair of protons (provided as (H2)+ ion) can end up as H2O, both by breaking SiO2 bonds. Either O+ or Si+ ions are produced. Unclear, what happens with these new ions.

      • Harvey says:

        Gerald - thanks.
        Something odd has happened re the link - its not the one I intended. I'll try & rediscover the link I meant it to be!
        The paper you cite (thanks) is pretty much what I would have expected, & what Ive seen in other papers - but the one I *intended* to cite contradicted it, & included XPS & SIMS data.

        If an H2+ ion arrives, I would expect the two protons to 'go their separate ways' on impact, as the binding energy is far less than the impact energy, & there are a very large number of (mainly small angle) scattering events before it comes to rest. Can it really end up as H2O in that way to a significant extent? What fraction are H2+ as opposed to H+?

        Re time, more than usual available, as I'm at home recovering from surgery & strictly banned from working 🙁
        I wonder if some lingering after effect made be make the missleading pit about electron density & forget thats unfair without mentioning scattering rates, silly mistake.

      • Harvey says:

        Gerald, Ok, the link I meant to post was this one, Burke et al:
        http://www.sciencedirect.com/science/article/pii/S0019103510004264
        Its conclusion is:
        "5. Conclusion
        Laboratory simulations of keV proton irradiation of ilmenite and anorthite give an upper limit of 0.5% in band depth at 2.8–3 μm for lunar material. This implies that there is no evidence to support the hypothesis that solar wind protons impacting the lunar surface combine with oxygen in the regolith to form significant amounts of –OH/H2O. In particular, we find proton bombardment alone cannot form enough O–H bonds to explain the 3–14% depth of the 3 μm absorption in the recent spacecraft observations."

        This seems very different to what one might expect, & many, many papers such as the recent Schaible et al 2014 & the one you cite seem to say the opposite. His conclusions are (partial):
        5. Conclusions
        Irradiation of silicate solids with 2–
        10keVH+ions leads to the formation of SiOH complexes which can be identified using transmittance FTIR spectroscopy around 2.8μm (SiO-H stretch) and 9.9
        μm (Si-OH stretch).There is no evidence for the formation of water. The probability of formation of OH bonds per incomingproton is close to one for a pristine surface and falls exponentially with fluence as fewer oxygen are available to form new bonds.
        http://onlinelibrary.wiley.com/doi/10.1002/2014JE004650/abstract
        Schaible references Burke a fair bit & points to differences, H2+ v H+ & grain size for example, & R v T IR measurements.

        The Burke & Schaible papers are both UHV & avoid air exposure, a potential concern in some other work, indeed S highlights that fact.
        Whilst I cannot really reconcile two apparently contradictory papers, (which Ive not read every word of to be fair) the weight of evidence seems to be in favour of an SiOH fate for the protons, as one might expect. But a lot of that 'weight' seems to originate in non-UHV exposure, often with transfers in air, & so potentially suspect?
        However Burke et al use UHV, no exposure & add XPS & SIMS, not just FTIR, & is seems odd; maybe Ive misunderstood/missed something., I'll blame the anaesthetic if so 🙂
        If you have further comments Id be most interested.

        Again, to be clear, nothing here supports this mechanism as the origin of neutral water in the coma.

  • Prof Harvey Rutt says:

    Plasma physics is a rather complex subject.

    There is a tendency here for it to get rather grossly over simplified; unfortunately, not everything is in fact simple.
    These comments 'take no sides', they simply point out factors you really must take into account if arguing about plasma physics.
    To do this properly needs a rather thick book; several in fact; this is of necessity a very short violently incomplete summary, written whilst at home whilst unwell!
    Where good references exist I will leave the reader to get the detail there.
    Numerical examples are strictly *order of magnitude*.

    I'm sure some will complain Wiki references are outdated etc; frankly nonsense; these are references to absolutely basic, firmly established physics, accepted by everyone in the field - Alfven included! Not just 'astro plasma physicists, all plasma physicists.

    A concept absolutely central to plasma physics is that of Debye length, never mentioned here.
    It is well explained in Wiki.
    http://en.m.wikipedia.org/wiki/Debye_length
    Essentially the Debye length is the scale over which the plasma must be electrically neutral. On smaller scales, you 'see individual particles', on larger scales you 'see plasma'.
    Many plasma phenomena are on a scale related to the Debye length - double layers for example are typically around ten Debye lengths across. On scales short compared to it, neutrality can be violated.
    In interplanetary plasmas, Debye lengths of order tens of metres might be typical. In a simple lab glow discharge, far shorter, order 10^-4m but very varied. Near 67P the Debye length will probably fall, further out rise to that ~~10m scale.

    There is confusion about 'currents' as opposed to 'wind'.
    A current implies a net flow of charge. If we pass a current through a plasma between two electrodes in the lab, and complete the circuit with a power supply, electrons move one direction, positive ions the other. In every volume a few Debye lengths on a side, it remains neutral, electrons and ions entering and leaving to keep it so. There is a net current flow, mainly carried by the much lighter electrons.
    Importantly, this can generate a magnetic field.
    But consider a case where the plasma is permitted to expand isotropically into a larger space. At the front edge the lighter, faster electrons 'get ahead' and are 'pulled back by' the slower ions, and there is a structure on a Debye length scale. (See ambipolar diffusion, http://en.m.wikipedia.org/wiki/Ambipolar_diffusion) but behind that it remains neutral on the Debye scale; electrons and ions expand *together* to maintain neutrality; its a plasma, it's a flow - but there is no net charge transfer, so no net current, and no magnetic field is generated to first order, away from that leading edge Debye length scale region.

    If there is an externally imposed magnetic field, as is the case in interplanetary plasmas with the solar field, it really goes beyond what I can do here. Perhaps the most crucial thing to look up is the Parker spiral, see
    http://en.m.wikipedia.org/wiki/Heliospheric_current_sheet

    It is often asserted that plasma is a conductor - it is, but not a perfect one, and the concept is complex in the presence of a magnetic field.
    In the absence of a field, the conductivity scales linearly with the electron density. The electron density in copper is some 8*10^22/cc, the solar wind density of order typically less than ten.
    So it's 'a good conductor' compared to hard vacuum, not compared to copper, or even a Tokamak plasma with ne maybe 10^20 (which is why ohmic heating is hard and needs huge currents.)
    With no magnetic field, conductivity is a simple single number, a scalar. So very low density plasmas typical of interplanetary space, with very low particle densities, are actually not very good conductors - but do indeed conduct. It's a relative term.
    Once you add a magnetic field, it gets complicated; the conductivity becomes a tensor, and depends on the orientation of current flow relative to the electric and magnetic fields. In general the values are lower than those with no field, highest for I//B. The best simple description I found is here; but for this, math is unavoidable.
    http://theory.physics.helsinki.fi/~xfiles/plasma/07/lect07/Collisions_conductivity.pdf
    A final matter, which relates not only to plasma physics, but much that goes on the the coma, is that of (energy dependent) cross sections for processes.
    There are a virtually infinite number of processes one can suggest, of the form A+B->C or A+B->C+D etc. The question is, which ones actually happen at a significant rate? Here A,B,C,D could be charged particles, photons, neutrals, ions, molecules. Note that if both A and B are massive particles, it is difficult to simultaneously conserve energy and momentum for a single product C.
    Which processes happen is determined by the densities of the species A and B *and their energies*. The probability it then determined by the 'cross section' for that process, which has units of m^2.
    Description of how cross sections are used in beam on target processes can be found here
    http://en.m.wikipedia.org/wiki/Cross_section_(physics)
    And in reacting species here
    http://en.m.wikipedia.org/wiki/Collision_theory
    Cross sections can depend extremely strongly on energy; in a thermal situation, one averages over the spectrum. There are often resonances in the spectrum. A relevant example would be that if a product species has a low binding energy, a negative ion, a molecule, it is unlikely to form in a high energy collision - low cross section - much more likely in a low energy - high cross section.
    Basically, one can suggest any process; but without reference to the densities, energy spectra, and cross sections for the reaction, one can say little or nothing about its likely importance. Many have been measured in the lab and are well known.

    Discussions which simply ignore the above factors are frankly little more than so much hot air. None are remotely contentious, all supported times over in a huge variety of situations.
    I may of course have slipped up somewhere, I'm not infallible, physics based corrections welcome.

    • Gerald says:

      Not a correction, but some short hint about tensors: A tensor is a generalization of vector and matrix to n-dimensional "number cuboids / hyperrectangles", together with rules of arithmetic.
      In the case of the current it's a 3x3 matrix. Such a matrix is defined for each point in the considered space, sometimes called a tensor field.

  • Prof Harvey Rutt says:

    One correction to the above, a point which I've made misleading to the extent of being partially incorrect, sorry.

    Conductivity is only proportional to ne for a constant electron-neutral collision frequency. The very low neutral background density will push the conductivity back up in very low density regions - but it will fall in the higher neutral density regions close to the nucleus.
    Which just emphasises the complexity.
    However the approximations used in deriving the conductivity will break down at 'high' current densities (actually,rather small) and reduce the apparent conductivity; it's the zero J limit.

    • Harvey says:

      There is a free program that might interest some here. It is very widely used & well established. It uses Monte Carlo methods, & I usually run it on a rather brutal work PC, but it does run acceptably on my decent but more normal home machine. I dont think it makes good use of the big machine in fact. To start to get any real idea of what is going on I'd run at least 1000 input ions; to get any accuracy on low yield sputter events etc, that might be100,000 & could be overnight.

      **I TAKE NO RESPONSIBILITY AT ALL IF YOU MESS UP YOUR PC OR CATCH A VIRUS DOING WHAT FOLLOWS*! It worked fine for me on several machines, but you try *AT YOUR OWN RISK - IF IN DOUBT *DON'T*

      The program is TRIM
      http://www.srim.org/
      It comes as a self extracting .exe & installs ok.
      The 'pro' version does 3D plots, bigger & slower but is still free.

      There is a frequent problem with it, many machines do not have the file Msvbvm50.dll which it needs. If you download Msvbvm50.exe *FROM MICROSOFT*
      http://support.microsoft.com/kb/180071
      into a temp directory & run it there, it will extract the .dll & put it in the right place. I strongly advise *AGAINST* downloading that file anywhere else than Microsoft; if you do at best you will pick up a load of irritating trash, at worst something really nasty.

      The TRIM interface is clunky, but pretty obvious & intuitive. You set up your substrate (which can be layered) , implant ion, & energy, & off it goes; it can take a while. You will need to fool around with it, changing scales, enrgies etc, but its really not difficult. To see sputtering you need to change the option in the DAMAGE window.
      SRIM produces a table of ranges, not pretty Monte Carlo plots. You may need to use a bit of imagination if you use to drop down lists of target materials to approximate what you want, or 'synthesize it' from the periodic table & %'s.

      Of course its not perfect, its an approximation etc etc etc - but it is a very widely used code & generally pretty reliable in my experience (I have used it for real stuff, not just plaing here.)

      I stress again; AT YOUR OWN RISK; if nervous, or less than computer literate, DON'T DO IT.

  • Gerald says:

    I think, I've identified a possible root cause for the misunderastndings regarding the electric universe model.
    The key sentence is found in the article
    http://en.m.wikipedia.org/wiki/Heliospheric_current_sheet :

    "The electric current in the heliospheric current sheet has a radial component (directed inward) as well as an azimuthal component, the radial circuit being closed by outward currents aligned with the Sun's magnetic field in the solar polar regions."

    The radial component of the circuit is closed, such that the Sun plays the role of anode AND cathode. This avoids the huge electrostatic charges and strong fields, which could have lead to the discharging proposed by the electric universe model.

    Although I think, that the referenced Wikipedia article is a much simplified idea with respect to the actual heliosphere. We'll certainly get closed current loops completely outside the Sun, entangled with closed magnetic field "lines".

    • THOMAS says:

      @ Gerald

      “I think, I've identified a possible root cause for the misunderastndings regarding the electric universe model.
      The key sentence is found in the article
      http://en.m.wikipedia.org/wiki/Heliospheric_current_sheet »

      Why not, but I’m not convinced that three lines from a fairly succinct Wikipedia article will be sufficient to undermine the foundations of the electric universe model. You actually seem to intuit this problem yourself in your conclusion:

      “Although I think, that the referenced Wikipedia article is a much simplified idea with respect to the actual heliosphere. We'll certainly get closed current loops completely outside the Sun, entangled with closed magnetic field "lines".

      As you probably know, the electrical engineers who make up the bulk of the EU theorists find the whole notion of “magnetic field lines” on the Sun and their alleged propensity to “reconnect” causing solar flares and CMEs complete and utter nonsense.

      Out of curiosity, I’ve just read through the Wiki article on “Magnetic Reconnection” http://en.wikipedia.org/wiki/Magnetic_reconnection and found the following paragraph:

      “A current problem in plasma physics is that observed reconnection happens much faster than predicted by MHD in highLundquist number plasmas: solar flares, for example, proceed 13-14 orders of magnitude faster than a naive calculation would suggest, and several orders of magnitude faster than current theoretical models that include turbulence and kinetic effects. There are two competing theories to explain the discrepancy. One posits that the electromagnetic turbulence in the boundary layer is sufficiently strong to scatter electrons, raising the plasma's local resistivity. This would allow the magnetic flux to diffuse faster. »

      Houston, we have a problem… “13-14 orders of magnitude” sounds rather a lot to me and in any self-respecting scientific method would be sufficient to not only falsify the theory (of “Magnetic Reconnection”) but to totally ridicule it. (No problem of lack of numbers or equations here, presumably, to give the “13-14 orders of magnitude” finding…).

      What astounds me most in this paragraph, however, are the last 3 sentences, starting with “There are two competing theories to explain the discrepancy.” The problem is that only “one” of these two “competing theories” is then actually summarized. I kid you not! I have not amputated the text: you can go and see for yourself in the article (http://en.wikipedia.org/wiki/Magnetic_reconnection).

      One is left to assume that the *other* “competing theory” is *NOT* summarized because it is literally unmentionable (a veritable Voldemort-style “theory-that-must-not-be-named”…!): immensely powerful electric currents (with catastrophic overload/short circuits regularly causing solar flares and CMEs).

      Unless anyone knows of another possible explanation….

      • Gerald says:

        Sometimes a basic misunderstanding can be pinned down to three lines, or even to 1 bit.

        About the 13 to 14 orders of magnitude:
        That has been the introduction and motivation to the theoretical approaches that follow (the "competing theories"). Just read on.
        The paragraph about collisionless reconnection closes the residual gap.
        http://en.wikipedia.org/wiki/Magnetic_reconnection#Collisionless_reconnection
        Although I wouldn't be surprised about future refinements, since it's a rather complex topic.

      • Prof Harvey Rutt says:

        How do you 'undermine the foundations of' something that simply doesn't have any foundations? There simply is, in the normally accepted scientific meaning of the word, no 'EU theory'. I suppose one might call it a conjecture, a hypothesis. A 'theory' in such a context is a body not only of words, but equations, often computer models, numerical results compared to observation, quantifyably testable predictions etc. In fact none of this exists for the 'EU theory'. All we have is (lots of) words.

        When I first encountered this, I browsed the Thunderbolts web site. Very glossy; virtually content free. Lots of textbook equations; no development of them, no numbers. Forty minute talks with no equations at all, full of egregious errors. Much time attacking the conventional theories, almost none developing their own. The 'neutrino problem' is an excellent example. There is no neutrino problem any more; essentially solar physics lead to a new understanding of neutrino physics. Importantly, *that has been confirmed times over by independent terrestrial measurements*; that's how we do things in *science*. The standard solar model is now in good agreement with measurements. In contrast there is no detailed EU prediction of neutrino production at all to compare to experiment. Yet somehow this gets distorted into support for the EU camp.

        It's clear the EU camp has no understanding at all of the extensive body of work on space plasma physics. A senior member stands up and say 'magnetic reconnection doesn't exist' (more or less verbatim.) No, in electrical engineering it doesn't. In plasma physics it most certainly does, the equations predict it (in the presence of finite resistivity), it's observed in multiple scenarios, in the lab, in space - there are even dedicated experiments on it. But, apparently, it doesn't exist, just because he says it doesn't, no other evidence at all.

        Another thing one might look at is the qualifications of the 'leading lights'. None of them has a substantial academic pedigree in this field in terms of qualifications, publications, Fellow of major Societies etc. So either they are brilliant Mavericks, bravely carving out a new route - or those who couldn't make it in real science, living in a fantasy world, running content free, incestuous conferences where no one ever asks difficult questions, with a distinctly commercial look to them.

        I'll stick with real science.

  • Prof Harvey Rutt says:

    He simply means Sweet Parker v. Petschek..
    if the EU community spent the time on developing real models it spends on conspiracy type theories, it might get somewhere.
    It is fully acknowledged this is a problem area for the standard models; nobody denies that. However no real competing EU model has ever been presented that I can find, just hand waving words. Please point me to a proper, developed model with numerical results and comparison to data.

  • Prof Harvey Rutt says:

    It is interesting that you highlight the dominance of electrical engineers in the EU 'theory'. That is indeed one of its problems.

    Magnetic reconnection, and indeed many other space plasma phenomena, do not happen in any 'electrical engineering context'. That is the world of iron cores and copper coils, which have current paths and physical positions strictly constrained. Currents are purely electron carried. There is nothing analogous to these effects in 'that world'.

    These are *plasma* phenomena, and there is no doubt whatever about their existence and that they satisfy the rules of magneto hydrodynamics etc. It's amusing that they miss the whole point about the very medium whose importance they stress.

    It happens that I trained as an electronic engineer, and later half converted into a physicist. There is no conflict whatever.

  • logan says:

    Just mMaybe here we have part of the missing profound energy budget. Not a magnetosphere in the custom way, but more of a 'magneto-atmosphere'. Let's call it MAS along this arguments.
    MAS is static relative to Sun and gyratory relative to 67P. MAS is the magnet, and conductive dust in 67P is the wire. You don't need planetary conductivity. You don't even need macro conductivity. You just need micro conductivity [MAS acts as gyrating magnet!]. Even more, you need resistivity [more than conductivity] in order to generate internal heat.
    So, here we have our 'cooking method': magneto-inducted, parasitic currents, micro scales, pressure bags, etc. 🙂

  • Prof Harvey Rutt says:

    Capta problems.
    Logan
    At 1AU, Earth or bit radius
    Solar radiation power density about 1.3kW per metre squared.
    Solar wind power density, around microwatts, tens of microwatts, per metre squared.
    Please check my sums, anyone including me can slip up.

    So radiation is fourteen or fifteen orders of magnitude larger. Which seems the more likely source of power?

    But solar wind could concentrate, solar radiation cannot. That would give huge signals in the magnetic field, plasma signals, Ampnd optical spectra, none of which is seen.
    The comet has virtually no magnetic field itself; it's moving plasma distorts the interplanetary field, very weak, nT.

    • logan says:

      Thanks for answering, Prof Harvey Rutt 🙂

      I was thinking of 10 orders of magnitude. Why are you making it ten thousand times smaller? 😉

      Are you considering the size of the comet's bow shock? That's the size of the magneto-focusing lens. [Fig. 3, Page 6 of the the comet-tutorial.pdf]. And it's quite a strong lens according to this figure.

      Should not dismiss so easily this 'focusing' effect of what eventually would become a paraboloid on starting the shock. [Right now 67P 'MAS' should have at least one big, ellipsoidal, soft focus zone, the second probably magneto-turbulance erased] Just remembering that neck's zone formerly called 'the singularity' and now this second one in the Comet watch 16 January. Also throwing into the speculation hat the highly refractive nature of the material's structural framing. Even if little, localized heat [and pressure] should eventually capitalize across months of high activity.

      On 'winding' by your side, that 'MAS' focal zone could be well outside of 67P surface, [at this moment, as it falls faster into our Sun, the argument could not hold on. Here you have a 'necking' mechanism].

      Adding too, the 'Great Walls' quite probably are more solid, dense and structurally crystalline than the 'core' material. If so, they could be relatively efficient transporting agents of heat, or energy, in a general way.

  • logan says:

    When the shock bow forms eventually, solar wind power delivered at surface will be negligible. Arguments will have to be about acting field forces, their geometry and density. [And -of course- the EM spectra].

  • Steven says:

    Now we just need to stop pretending the water originates from "hidden ices" and accept how it gets there in the first place. Got half of it figured out - now connect the dots and realize no water is found on comets because it is created electrically in the coma from negative silicates machined of it's surface from proton bombardment.

    http://www.space.com/24422-solar-wind-makes-water-star-dust.html

    http://www.space.com/27377-moon-water-origin-solar-wind.html

    To be honest we should all realize no water has ever been detected on a comet except rare shallow patches of frost from condensation from the halo. OH not H2O is detected and they misconstrue that to mean water, when OH is naturally created from bombarding negative silicates with protons without water at all being present. And is why the OH is out or proportion to the H radicals if the source was indeed water.

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