Rosetta and Philae find comet not magnetised

This new result was just presented at EGU2015 and is published in Science Express today. The text is mirrored from our news story on the main ESA web portal

Measurements made by Rosetta and Philae during the probe’s multiple landings on Comet 67P/Churyumov-Gerasimenko show that the comet’s nucleus is not magnetised.

ESA_Rosetta_Philae_RPC_ROMAPStudying the properties of a comet can provide clues to the role that magnetic fields played in the formation of Solar System bodies almost 4.6 billion years ago. The infant Solar System was once nothing more than a swirling disc of gas and dust but, within a few million years, the Sun burst into life in the centre of this turbulent disc, with the leftover material going into forming the asteroids, comets, moons and planets.

The dust contained an appreciable fraction of iron, some of it in the form of magnetite. Indeed, millimetre-sized grains of magnetic materials have been found in meteorites, indicating their presence in the early Solar System.

This leads scientists to believe that magnetic fields threading through the proto-planetary disc could have played an important role in moving material around as it started to clump together to form larger bodies.

But it remains unclear as to how crucial magnetic fields were later on in this accretion process, as the building blocks grew to centimetres, metres and then tens of metres across, before gravity started to dominate when they grew to hundreds of metres and kilometres in scale.

Some theories concerning the aggregation of magnetic and non-magnetic dust particles show that the resulting bigger objects could also remain magnetised, allowing them to also be influenced by the magnetic fields of the proto-planetary disc.

ESA_Rosetta_Philae_trajectoryBecause comets contain some of the most pristine materials in the Solar System, they offer a natural laboratory for investigating whether or not these larger chunks could have remained magnetised. However, detecting the magnetic field of comets has proven difficult in previous missions, which have typically made rapid flybys, relatively far from comet nuclei.

It has taken the proximity of ESA’s Rosetta orbiter to Comet 67P/Churyumov-Gerasimenko, and the measurements made much closer to and at the surface by its lander Philae, to provide the first detailed investigation of the magnetic properties of a comet nucleus.

Philae’s magnetic field measuring instrument is the Rosetta Lander Magnetometer and Plasma Monitor (ROMAP), while Rosetta carries a magnetometer as part of the Rosetta Plasma Consortium suite of sensors (RPC-MAG).

Changes in the magnetic field surrounding Rosetta allowed RPC-MAG to detect the moment when Philae was deployed in the morning of 12 November 2014.

Then, by sensing periodic variations in the measured external magnetic field and motions in its boom arm, ROMAP was able to detect the touchdown events and determine the orientation of Philae over the following hours. Combined with information from the CONSERT experiment that provided an estimate of the final landing site location, timing information, images from Rosetta’s OSIRIS camera, assumptions about the gravity of the comet, and measurements of its shape, it was possible to determine Philae’s trajectory.

The mission teams soon discovered that Philae not only touched down once at Agilkia, but also came into contact with the comet’s surface four times in fact – including a grazing collision with a surface feature that sent it tumbling towards the final touchdown point at Abydos. This complex trajectory turned out to be scientifically beneficial to the ROMAP team.

“The unplanned flight across the surface actually meant we could collect precise magnetic field measurements with Philae at the four points we made contact with, and at a range of heights above the surface,” says Hans-Ulrich Auster, co-principal investigator of ROMAP and lead author of the results published in the journal Science and presented at the European Geosciences Union General Assembly in Vienna, Austria, today.

ESA_Rosetta_Philae_ROMAP_collisionThe multiple descents and ascents meant that the team could compare measurements made on the inward and outward journeys to and from each contact point, and as it flew across the surface.

ROMAP measured a magnetic field during these sequences, but found that its strength did not depend on the height or location of Philae above the surface. This is not consistent with the nucleus itself being responsible for that field.

“If the surface was magnetised, we would have expected to see a clear increase in the magnetic field readings as we got closer and closer to the surface,” explains Hans-Ulrich. “But this was not the case at any of the locations we visited, so we conclude that Comet 67P/Churyumov-Gerasimenko is a remarkably non-magnetic object.”

Instead, the magnetic field that was measured was consistent with an external one, namely the influence of the solar wind interplanetary magnetic field near the comet nucleus. This conclusion is confirmed by the fact that variations in the field that were measured by Philae closely agree with those seen at the same time by Rosetta.

“During Philae’s landing, Rosetta was about 17 km above the surface, and we could provide complementary magnetic field readings that rule out any local magnetic anomalies in the comet’s surface materials,” says Karl-Heinz Glassmeier, principal investigator of RPC-MAG on board the orbiter and a co-author of the Science paper.

If large chunks of material on the surface of 67P/Churyumov-Gerasimenko were magnetised, ROMAP would have recorded additional variations in its signal as Philae flew over them.

“If any material is magnetised, it must be on a scale of less than one metre, below the spatial resolution of our measurements. And if Comet 67P/Churyumov-Gerasimenko is representative of all cometary nuclei, then we suggest that magnetic forces are unlikely to have played a role in the accumulation of planetary building blocks greater than one metre in size,” concludes Hans-Ulrich.

“It’s great to see the complementary nature of Rosetta and Philae’s measurements, working together to answer this simple, but important ‘yes-no’ question as to whether the comet is magnetised,” says Matt Taylor, ESA’s Rosetta project scientist.

 

Notes

“The non-magnetic nucleus of Comet 67P/Churyumov-Gerasimenko,” by H.-U. Auster et al. is published in Science Express on 14 April. (http://www.sciencemag.org/lookup/doi/10.1126/science.aaa5102)

Overall, the data show that the comet has an upper magnetic field magnitude of less than 2 nT at the cometary surface at multiple locations, with a specific magnetic moment of < 3.1 x 10^–5 Am^2/kg, less than known values for lunar material and meteorites measured on Earth.

About ROMAP: ROMAP is the Rosetta Lander Magnetometer and Plasma Monitor. The contributing institutions to ROMAP are: Institut für Geophysik und Extraterrestrische Physik, Technische Universität Braunschweig, Germany; Max-Planck Institut für Sonnensystemforschung, Göttingen, Germany; Hungarian Academy of Sciences Centre for Energy Research, Hungary; and Space Research Institute Graz, Austria. The co-principal investigators are Hans-Ulrich Auster (Technische Universität, Braunschweig) and István Apáthy, KFKI, Budapest, Hungary.

About RPC-MAG: RPC-MAG one of six instruments comprising the Rosetta Plasma Consortium. The fluxgate magnetometer (RPC-MAG) is led by Karl-Heinz Glassmeier, Technische Universität, Braunschweig, Germany.

Comments

90 Comments

  • Phil Stooke says:

    Re: the comment about the second bounce (why is it higher than the first) on the trajectory image – remember the nucleus has a very irregular shape and gravity field, so the height of the bounce is not likely to be intuitive – it’s not like a bouncing ball on Earth, losing energy at each bounce but in a constant gravity field with the same geometry each time.

  • harvey says:

    There is something else this rules out (not that it needed to.)

    Lets take a *really feeble* discharge current, say 1mA/cm^2 or 10A/m^2. That is very low by Lab standards & certainly wont do anything dramatic, let alone shift masses of neutrals & dust.
    Take, say, a 50m radius carrying 1mA/cm^2, and say 1km away.

    The resultant field is around 2*10^-5T
    The reported field is <2*10^-9T, some ten thousand times weaker.
    You can mess with the assumptions as you like; no way willl you drop the field by 10^4 – and the current density I've used is extremely low, you could argue for a thousamd or more times that.

    So maybe Philae was at the exact centre, or several fields *exactly* vector cancelled at both craft, or whatever; there is certain to be an explanation 🙂

    • originalJohn says:

      A discharge current occurs Harvey at the points of discharge, which are the regions of jet emission. Elsewhere where there is no visible discharge the current would be expected to be as low as you are surmising or lower, ie zero. So it would be reasonable that the current near these points on the surface might not be too different from the current and therefore the magnetic field strength 17 km above the surface where the orbiter was. It seems more likely that the lander touched down each time in one of those low or zero current areas as it was bouncing about on the small lobe when most of the discharge activity was in the neck region. No conclusion can be drawn about likely discharge current ( or associated magnetic field) until the typical jet current is known. If it has been measured it has yet to be published.
      Also random single point measurements are not of much value when trying to asses a magnetic field. A magnetic field is a three dimensional continuum and many points all around the nucleus must be measured to provide even a low resolution map of strength and distribution.
      Finally let us be clear here precisely what else has been demonstrated by this result. As the title of the post says the comet (nucleus) is not magnetised, within the sensitivity and resolution of the instruments. It does not therefore contain significant quantity of permanently magnetised material. This does not however preclude the possibility of the existence of a magnetic field associated with the nucleus. Refreshingly it is acknowledged that the solar wind has its own magnetic field which also acknowledges its electric current nature. It is the modification of the solar wind current and therefore magnetic field by the presence and behaviour of the comet nucleus that would establish the magnetic field associated with the nucleus. No enlightenment on this yet.

      • Gerald says:

        http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html
        B = mu_0 I / (2 pi r), with mu_0 = 4 pi 1e-7 T m / A

        Hence I = 2 pi r B / mu_0
        Set r = 2000 m, B = 2e-9 T, as upper bound according to magentometer measurements.
        We get I = 2 pi 2000 m 2e-9T / (4 pi 1e-7 T m / A) = 1000 m 2e-9 A / 1e-7 = 20 A.

        Hence the maximum possible total current in at least 2 km distance is 20 A to be consistent with the magnetometer measurements.

      • Harvey says:

        Of course the solar wind and the interplanetary field are linked, that’s been known for decades. It hardly needs ‘acknowledging’, it’s common knowledge.

        This discharge is supposedly moving LARGE amounts of neutral material out from the comet. We are never given an estimate of the currents involved by the EU ‘theory’, nor is the mechanism which accelerates the neutrals ever explained. (The ions are going the wrong way if the comet is negative as we are told!) So in default of anything from the ‘theory’, which never, ever gives quantitative values, I simply use a ridiculously low number.
        1mA/cm^2 is an EXTREMELY feeble discharge. It is simply not remotely credible it could produce the large scale matter transport Involved; you could run that off an uncooled electrode for years without a problem. Yet even this, over areas small compared to the so called ‘visible discharges’, at a credible distance, would produce a field vastly larger than that observed.
        Electric currents produce magnetic fields; fields at such a minute level, nT, identical at the two positions, over the bounce track of Philae, are a very good demonstration that there are no large currents anywhere nearby.

      • Harvey says:

        “Finally let us be clear here precisely what else has been demonstrated by this result. ”
        Indeed, let’s.
        What has been demonstrated is that there was no current of any significance within a small number of km of Philae at that time – barring bizarre and extremely improbable ‘cancellations’ etc.
        Gerald reaches exactly the same conclusion.

      • sjastro says:

        @originaljohn,

        In the context of an electric comet, your argument fails because of the assumption a magnetic field is only associated with a current.

        If the comet is carrying an electric charge, the comet’s electric field is simply the sum total of the individual electric fields of each charge on the surface.

        When the comet discharges at particular points, the electric field IN SPACE changes with time and a magnetic field is induced.
        Neither Philae nor Rosetta have to be located at a point of discharge or jet emission respectively, because the induced magnetic field is not caused by a current.

        The bottom line is the lack of an induced magnetic field is body blow to the existence of electric comets.

        • harvey says:

          Basically, nonsense; We have already demonstrated multiple times that the charge on the comet is negligible or it would have a ridiculous voltage.
          If discharges powerful enough to move significant amounts of material – by still utterly unexplained mechanisms – were present, both Gerald & I have shown what order of magnetic field might be expected under EXTREMELY conservative assumptions.
          The ~2nT at both Philae & Rosetta is fatal to this nonsense, not that anything will actually kill it off.

          • sjastro says:

            Just to make sure there is no point of confusion here Harvey, my post was directed against origiinaljohn’s claim that Philae and Rosetta needed to be located at a specific location in order to measure the magnetic field.

            Of course the charge on the comet would be ridiculously small.

            I want to make sure your use of the term nonsense is directed towards the right person.

          • harvey says:

            sjastro Sorry, the way this works its sometimes a bit unclear what a reply refers to. ‘Nonsense’ referred to the usual complete incomprehension of how plasma physics & electrical circuits work routinely displayed by our EU friends.

    • Kamal Lodaya says:

      originalJohn: I have read the electric theorists argue that electrons are stripped from the comet’s surface when it is in a negatively-charged environment far from the Sun (which is itself positively charged), to the point where one can see bright spots of current jetting out of the surface. The comet’s surface below the jet is therefore burnt out black. These electrons form a charged head around the comet.

      Are you saying there is no negatively-charged environment away from the Sun? Are large regions of the solar system always electrically neutral?

      • Harvey says:

        ‘Space’ (ie the tenuous interplanetary plasma) is neutral on a scale length greater than the Debye length. In interplanetary space, typically of the order on 10m. This scale length falls in regions of higher plasma density. This has been established times over by direct spacecraft measurement.
        If a local region becomes say electron deficient, it develops a positive charge, attracts electrons and self neutralises, and vice versa.
        On a scale less than the Debye length you start to see local fluctuations of both signs, until ultimately you are seeing single particles.

      • originalJohn says:

        Kamal Lodaya, the field is more strongly positive close to the anodic element, the Sun, and more strongly negative close to the cathode element, the heliosphere boundary. The comet would be expected to loose electrons and tend to acquire a more positive charge as it approached the Sun and gain electrons and acquire a more negative charge as it approached the cathode region, and so on with each orbit.

        No regions of the solar system are electrically neutral. It is permeated by the solar wind plasma, a stream of charged particles constituting an electric current that establishes the field. Despite what Harvey says, and I have explained it to him elsewhere, the Debye length determines the charge separated nature of the plasma.
        And although no instruments have been there it is thought also to apply to both the interstellar medium and the intergalactic medium. In other words the whole universe (or 99.9% of it) consists of charge separated plasma. It is rather unlikely that no electric current is flowing in it.

        • Kamal Lodaya says:

          originalJohn: So after peihelion, when the comet is moving away from the Sun, it has to gain electrons? Is the tail at that time the electrons moving into the comet nucleus?

          • originalJohn says:

            Whether it would gain electrons Kamal Lodaya would depend on what happened to its charge state during its passage through perihelion. If the discharge voltage ceased, and this has happened to other comets, it would have become balanced with the charge near the Sun, ie neutralised, then perhaps subsequently positively charged. Then as it moved away and if the negative potential gradient was strong enough it would be expected to discharge by absorbing electrons at the nucleus surface. Any surface reaction would be initiated by these electron collisions and positive ions would be discharged. It is however also possible that the nucleus remains negatively charged through perihelion and therefore continues to discharge in the same way as the approach phase until its charge equalises with the solar wind environment and the potential disappears briefly. It is never though going to become more charged (positive or negative) than its immediate environment. So it will only discharge by moving into a region of different charge, and there is a potential gradient in the solar electric field all the way to the boundary of the heliosphere.
            In at least two of its previous visitations the maximum intensity of discharge for 67P, including dust, occurred weeks after perihelion (as measured from Earth).

            The direction of motion of ions in the tail, as in any plasma would be positive ions and negative ions ( including electrons) in opposite directions, regardless of which way the tail was pointing. Which direction for each would depend on the charge on the nucleus..

            What is actually happening will be measurable by the orbiter.

          • Kamal Lodaya says:

            originalJohn: So the electric theory cannot explain whether a comet’s tail should be pointing towards the Sun or away from the Sun. According to the electric theory it all depends on what the difference in potential is at
            different times and at different places in the solar system environment, about which you seem coy to put yourself to the test (fair enough, I can’t even see how you would go about testing it). Your supposition is that at perihelion there is a huge transfer of positive ions from the Sun to the comet, and after perihelion it is these positive ions which form the tail. But what are these ions? According to the electric theory before perihelion the comet’s head is full of electrons, and after perihelion the comet’s head is full of positive ions. No mass difference is detectable, so does the theory predict that there is a huge discharge of positrons from the Sun to a comet at perihelion?

          • Kamal Lodaya says:

            Reading some more of the electric theorists, I think they would predict a difference. Before perihelion we have a tail made up of electrons. At perihelion the Sun packs the comet head with lots of positively charged hydrogen (which is the same as protons). So after perihelion there should be a tail made up of protons.

          • originalJohn says:

            I notice Kamal Lodaya that it appears to be a tactic of those who oppose the electrical explanation to try and “catch out” those who present it, as though that would nullify the whole paradigm. You do it but of course not only you. You would do better to consider your own beliefs a bit more carefully and try and catch yourselves out, because mostly you are simply believing what you are told.
            Perhaps you are aware that the comet coma and tail combination is an extremely complex phenomenon and in general poorly understood. There is also much rubbish talked in trying to define and describe it. I, having no more information than the next person, do not pretend to have a definitive explanation but I will give you my understanding in line with what I have said to you so far, and see if you catch me out.

            There are three discharge possibilities I can think of at and after perihelion. The first is that the discharge we see on approach, of the negatively charged nucleus, continues at and after perihelion. This is the most likely. In this case the tail ( which is an extension of the coma) will continue to point away from the Sun. The second is that the discharge will stop as the nucleus becomes equalised with the immediate solar environment.. Then there will be no visible coma or tail. The third is that the nucleus will collect sufficient positive charge near the Sun, after fully discharging, that it will start to discharge again as it moves, though decelerating, into the region of increasing negative potential further from the Sun. In this case it would be attracting electrons and discharging positive ions. So the question is which way would the tail point. My understanding is that it would still point away from the Sun, because the tail, itself a plasma, is formed by ions picked up from the coma by the solar wind current and the solar wind proton current, and some electron drift, always flows away from the Sun.
            There is also the more curved dust tail and this will always point away from the Sun.
            Finally I will remind you that some comets have displayed two ion tails, one normal one pointing away and a shorter one pointing towards the Sun. The shorter one has been held, as I understand, to be caused by electrons and other negative ions and the longer one by positive ions. Both however would consist of plasma and both would be carrying sufficient current to be in glow mode and thus visible..

            Oh and irrespective of the tail there is another discharge possibility which is explosive disintegration of the nucleus. This could happen at any time but with some past comets has usually occurred as the comet retreats from the Sun.

          • Kamal Lodaya says:

            No hard feelings, OriginalJohn, my tactic is in response to people who immediately start asking how the “sublimation theory” will explain this or that, whereas they have known everything all along.

            Kamal

        • harvey says:

          ” ……the field is more strongly positive close to the anodic element, the Sun, and more strongly negative close to the cathode element, ”
          “Fields” are described by vectors; they have a magnitude and a direction; they are not ‘positive’ or ‘negative’, terms primarily ascribed to scalars. So I have no idea what this means. If you cannot get basic physics/math terminology right, there is little hope for anything more complex.

          “The comet would be expected too……………”
          This of course just makes multiple assumptions, that the sun *is* positive, that there *is* some mysterious electron source in the ‘cathode region’ and some mechanism for that charge to accumulate & not self neutralise. *AND* it fails totally numerically; we are back to the comet ‘storing charge’ in outer orbit regions; to store enough to run a significant discharge even for minutes requires insane voltages as has been demonstrated numerically times over.

          “No regions of the solar system are electrically neutral. It is permeated by the solar wind plasma, …………….”
          The *definition* of ‘plasma’ which can be found in many places requires it to be approximately neutral. So this sentence is self contradictory.
          The first one to hit:
          http://dictionary.reference.com/browse/plasma
          ” Physics. a highly ionized gas containing an approximately equal number of positive ions and electrons. ” (Bit crude; some ions could be >1+)

          A homogeneous plasma is electrically neutral on a scale of a number of Debye lengths. Inhomogeneous plasmas (eg, wrt temperature) or those carrying currents can certainly build up charge separated regions, double layers etc, on a scale of maybe ten, a few tens, of Debye lengths or so. Beyond that scale, much beyond a few100m typically in interplanetary space, it’s neutral.

          • originalJohn says:

            The field exists because of a potential difference Harvey. Positive charge at the anode, negative at the cathode. with a potential gradient in between. The vector nature of a field is irrelevant to this.
            The electron source in the cathode region, flowing from the interstellar medium, is acknowledged by astronomers and astrophysicists. It is only mysterious to you.

            As for plasma you are relying on dictionary definitions but they are often wrong. A plasma is not a gas, It is a distinct state. Once the gas becomes ionised ( even partially) it is no longer a gas. It is a plasma and has properties and behaviour which no gas has. One of those properties is that it is a charge separated mediium despite having numerical neutrality. You do not understand this because you do not understand what Debye length is and its significance. I have explained this to you now several times so no more lessons from me. You have convinced yourself of an opposite meaning for Debye length and everything you say about plasma that follows from that is wrong. You need to read it up again and this time think a bit more about it and what would make sense.

            The active region of the Sun is itself a plasma and plasma does not self neutralise, because of the Debye length constraint.

          • harvey says:

            Unfortunately every single professional plasma physicist thinks otherwise.

            One of hundreds:
            http://homepages.cae.wisc.edu/~callen/chap1.pdf
            “On length scales longer than the Debye length a plasma responds collectively to a given charge, charge perturbation, or imposed electric field. The Debye
            shielding distance is the maximum scale length over which a plasma can depart significantly from charge neutrality””

            We can’t paste formulae here; I can I’m afraid do the math; it means exactly what this says.

  • logan says:

    There’s something I don’t understand: When initial magnetic data on the landing were provided by IGEP from TUB, the Institute included a graph showing B[nT] on the hundred level for ROMAP.

    • harvey says:

      Logan
      If I recall correctly those were the actual measurement, uncorrected for the field Philae itself generates.
      They were useful because as Philae bounces etc, the arm holding the magnetometer moves in Philae’s own field & provides information.
      These are the true fields with Philae’s contribution removed.
      I’m pretty sure that is correct, but have not browsed back to check.

  • Kamal Lodaya says:

    If I understand what is said correctly, the observed magnetic field cannot be attributed to the comet nucleus, it is possibly of an interplanetary nature. Earlier we had a few posts on the “song of the comet”. If that is attributed to the comet environment where is it coming from? Is it also something of an interplanetary nature?

    • THOMAS says:

      I suggest that it may indeed be coming from the “comet environment” and more precisely from the “magnetosphere” which is reported to have formed around 67P (http://blogs.esa.int/rosetta/2015/01/22/watching-the-birth-of-a-comet-magnetosphere/), detected with some surprise as early as last October at the latest (and presumably much earlier even, since the ‘Science’ article reporting the result was only “received for publication” on 10 October 2014: http://www.sciencemag.org/content/347/6220/aaa0571.abstract).

      In the EU model, the so-called “magnetosphere” is better known as a “double layer” or “plasma sheath”, which, as described by the 1970 Physics Nobel Prize-winner Hannes Alfven (http://en.wikipedia.org/wiki/Hannes_Alfv%C3%A9n), self-organizes to separate regions of positive and negative charge in certain regions of space. The consequent electrical activity is likely what is producing the comet’s “song”.

      • Kamal Lodaya says:

        Thomas: Where precisely did Alfven say that a double layer self-organizes to separate regions of positive and negative charge in certain regions of space?

      • Kamal Lodaya says:

        Hannes Alfvén described double layers in several contexts, but not in the context of comets. Alfvén took it for granted that dust and gas from the comet nucleus formed the comet’s “coma” (head) and the
        comet’s dust tail was formed due to radiation pressure. Alfvén was interested in how ion tails of comets formed as a result of interaction with (what we would today call) the solar “wind”.

        I have not been able to find a reference to Alfvén
        speaking about self-organization of double layers in the context of comets. So the assertion that there is such a self-organization which separates positive and negative charges in certain regions of space in the vicinity of a comet should be attributed to Thomas and not to Alfvén. Thomas also thinks therefore there is electrical activity which is likely to produce the comet’s “song”.

        • THOMAS says:

          @ Kamal Lodaya

          “Hannes Alfvén described double layers in several contexts, but not in the context of comets.”

          I never claimed he did: kindly re-read my comment above.

          “… the assertion that there is such a self-organization which separates positive and negative charges in certain regions of space in the vicinity of a comet should be attributed to Thomas and not to Alfvén.”

          Ditto. This is a simple Straw Man argument, Kamal Lodaya. Alfven obviously did not speak of double layers/plasma sheaths “in the vicinity of” COMETS, quite simply because he died well before we had acquired the images of comet nuclei we now have. I never said he did. It is I (among others) who am making the link between double layers and comets, as was perfectly clear in my initial comment. It was simply Alfven’s insight about the existence of double layers in space, above all with respect to the Sun (see: http://www.holoscience.com/wp/alfven-triumphs-again-again/) which made this connection possible. Please quote more accurately in future.

        • Kamal Lodaya says:

          Thomas, if I may quibble with you, I have not found a reference to Alfvén speaking about self-organization of double layers at all. Perhaps that can also be attributed to you and not to him. To quote him:

          “The sun acts as a unipolar inductor … producing a current which during odd solar cycles goes outward … in even solar cycles the direction of the current is reversed.”

          So Alfvén is not saying anything about the Sun being the anodic element as the EU people have been saying on this blog. My guess is that the sunspot cycles were a problem of great interest to him. But that is a little far from comets.

          Kamal

          • THOMAS says:

            @ Kamal Lodaya

            Quibble away, by all means.

            If your search for “a reference to Alfvén speaking about self-organization of double layers” proved to be fruitless, it’s quite simply because you didn’t look in the right place….

            The best place to go was to the abstract of one of Alfvén’s own articles entitled “Double layers and circuits in astrophysics”, published in IEEE Transactions on Plasma Science , vol. PS-14, Dec. 1986, p. 779-793.

            (Incidentally, in this abstract, he also takes a swipe at the steadfast refusal of “mainstream” astrophysicists to take any account of indisputably challenging findings in plasma cosmology which, in 1986, had already been known, on the basis of *observational* evidence, for “50 years”).

            I quote:

            “ABSRACT: A simple circuit is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to THE PREDICTION OF TWO DOUBLE LAYERS ON THE SUN’S AXIS which may give radiations detectable from earth. Double layers in space should be classified as a new type of celestial object. It is suggested that X-ray and gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). The way the most used textbooks in astrophysics treat concepts like double layers, critical velocity, pinch effects and circuits was studied. It is found that students using these textbooks remain essentially ignorant of even the existence of these, although some of the phenomena were discovered 50 yr ago” (my capitals for emphasis)
            (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1986ITPS…14..779A&db_key=AST&data_type=HTML&format=&high=42ca922c9c02197).

            If it’s the term “self-organizing” that you are quibbling with, the only fault that can be found with it is that it is a tautology: double layers are, by definition, “self-organizing” with respect to the oppositely charged particles, hence the electric currents, which are present in the area of space where they form.

            You continue:
            “So Alfvén is not saying anything about the Sun being the anodic element as the EU people have been saying on this blog.”

            What he actually said in the body of the article I give the abstract of above, about his prediction of “two double layers on the sun’s axis” is:

            “Since the time of Langmuir, we know that a double layer is a plasma formation by which a plasma — in the physical meaning of this word — protects itself from the environment. It is analogous to a cell wall by which a plasma – in the biological meaning of this word – protects itself from the environment. If an electric discharge is produced between a cathode and an anode THERE IS A DOUBLE LAYER, CALLED A CATHODE SHEATH, PRODUCED NEAR THE CATHODE that accelerates electrons which carry a current through the plasma. A positive space charge separates the cathode sheath from the plasma. Similarly, A DOUBLE LAYER IS SET UP NEAR THE ANODE, protecting the plasma from this electrode. Again, a space charge constitutes the border between the double layer and the plasma. All these double layers carry electric currents.” (my capitals for emphasis)

            I feel flattered and honoured that you should wish to attribute the idea to me but, as you see, I was beaten to it by Hannes Alfen, who was awarded the Physics Nobel Prize for his work in this field way back in 1970.

            As for your 3-line quotation from Alfven’s writings, are you seriously claiming that what he says in these three lines in some way belies or cancels out the rest of his pioneering work in plasma physics, including everything he wrote about double layers? If so, could you please explain how? In reality, there is absolutely no contradiction between the ideas he is expressing. If you truly wish to serve the standard theory cause, I advise you to do a lot more research and a little more thinking before embarking on further “quibbles” like this one.

          • Kamal Lodaya says:

            Thomas: All I pointed out is that you are misappropriating Alfvén for your cause. The quotes you have given from his work do not convince me otherwise. It is a pity that the Soho missions happened just after he passed away in 1995. He would have liked the new data and the lovely pictures we have of the Sun’s activity now.

            I am no crusader. I am curious about comets and delighted by what I am learning from this mission.

          • Gerald says:

            In 1986 the source for GRBs was pure speculation.
            No big deal, that Alfvén has been wrong.

            “Hundreds of theoretical models were proposed to explain these bursts in the years following their discovery, such as collisions between comets and neutron stars.[6] Little information was available to verify these models until the 1997 detection of the first X-ray and optical afterglows and direct measurement of their redshifts using optical spectroscopy, and thus their distances and energy outputs.”
            http://en.wikipedia.org/wiki/Gamma-ray_burst

          • THOMAS says:

            @ Kamal Lodaya

            I don’t have a “cause”, except to make a little more widely known the perfectly respectable, well-documented and scientifically sound discipline of plasma cosmology of which Alfven was one of the major founding fathers and which I (along with many others) believe the behavior of comets to be a spectacular manifestation of. Accusing me of “misappropriating” Alfven in suggesting the principle of double layers to be applicable to comets would be like accusing someone of misappropriating Einstein in his applying the hypothesized principle of curved spacetime to so-called gravitational lensing…

      • martin says:

        thomas said: “In the EU model, the so-called “magnetosphere” is better known as a “double layer” or “plasma sheath”, which, as described by the 1970 Physics Nobel Prize-winner Hannes Alfven (http://en.wikipedia.org/wiki/Hannes_Alfv%C3%A9n), self-organizes to separate regions of positive and negative charge in certain regions of space. The consequent electrical activity is likely what is producing the comet’s “song”.”

        One can only reply with Pauli here: this is not even wrong
        (http://en.wikipedia.org/wiki/Not_even_wrong)

    • logan says:

      Even if not generating magnetism of her own, 67P is not ‘transparent’ to it. Has to be some kind of play in [ambient] magnetism scattering back to ROSETTA in its slow transit. Also diffraction and absorption being issues.

      Already we have seen geometry being relevant at Coraline’s general structure. This could bring patterns and regularities to the magnetic ‘songs’.

      interesting question. Hopping to see more comments on this.

      • harvey says:

        Logan
        In fact the body of 67P probably is pretty much ‘transparent’ to magnetic fields. Terms like scattering, diffraction, & absorption apply primarily to propagating EM (& other) waves, not to static fields. We now know it has no large-scale field; it seems likely its permeability is close to one; we expect (& CONSERT data, limited) confirms, its an insulator. In these circumstances the solid body of the comet has little or no effect on the field.

        The plasma around the comet is another matter, because it is photoionised & so conducting, expanding & moving supersonically through the interplanetary field & plasma which, if outgassing is strong enough, generates a bow shock & strongly distorts the field.

        • logan says:

          Thanks for answering, Harvey 🙂

          How do you interpret the pattern delta between RPC and ROMAP at the green graph?

          On making use of the exception of scales < 1m, I am allowing myself to differ, and stand on 67P being slightly conductor and capacitive.

          "…not [apply] to static fields.": From 67P's frame even the interplanetary magnetic field is not static.

          Fully accepting your comment about local magnetosphere being the dominant field here.

          Nowadays, A 4 min graph doesn't have a lot to say about it. What a 4 min graph says is about 67P itself.

          • harvey says:

            Logan
            A propagating wave satisfies the wave equation, & has its only velocity & dispersion curve. These are the things to which diffraction etc primarily apply.
            The fact that 67P itself is moving through the interplanetary field accompanied by its photoinised plasma & generating a bow shock (possibly by now) is quite different. no propagating wave is involved.
            Static, non ferromagnetic conductors such as copper are also ‘transparent’ with a permeability of ~1.
            If moving through a nonuniform field, or if the field is time varying (same thing) eddy currents in the conductor are generated whose fields then modify the local field. However 67P is pretty certainly far too highly resistive for that to be significant.

            Essentially the ‘sold body’ of 67P will have essentially no effect on the local field; its surrounding plasma does.

          • logan says:

            Hi, Harvey:
            “…However 67P is pretty certainly far too highly resistive for that to be significant [eddy currents].”
            Couldn’t find where you jumped to this one.

        • logan says:

          What if there were parasitic ALTERNATE currents at 12h per cycle?

          Could think of layers acting as capacitors: As a post accretion/grow feature, the space in between should be lower on dust, and act as insulator. [Could also imagine of conducting/insulating/capacitive structures at the micro scale].

          Sounds extremely slow. Nothing able to pound a magnetometer needle. But If extremely refractory materials added into the model, Then heat could accumulate at profound.

        • originalJohn says:

          Logan, as you and I know photoionisation as the predominant source of plasma in the coma is a hypothesis. Photoionisation is a weak effect. A much more likely source of most of the plasma is the production in the plasma discharge we see in the jets. In due course the jets will be measured and analysed and this will be obvious.

          • originalJohn says:

            Oh and bow shock Logan we have touched on before. It is a ridiculous but often invoked mechanical concept. Those who go on about how low the density of the heliosphere is conveniently forget it when they want to. And they forget how small a proton is ( 10 power 22 protons in a gnat is a good way to think of it). The chances of any collision between particles influencing the boundary of coma are virtually non existent. Plasma effects however are a different story.

          • harvey says:

            The fact that we’ve flown spacecraft right through bow shocks & seen structures pretty much as expected is a slight problem of course.

            And you seem to have forgotten protons are *charged*; hard-body collisions are relevant to the LHC, not to bow shock formation. However in fact astrophysical bow shocks are largely collision less.

            http://en.wikipedia.org/wiki/Shock_waves_in_astrophysics
            http://en.wikipedia.org/wiki/Bow_shocks_in_astrophysics

            Photoionisation as the driving force is supported by a huge body of data & modelling; but as usual, you know better.

          • sjastro says:

            “Photoionisation is a weak effect…….”

            Perhaps you would like to explain the existence of the Earth’s ionisphere if photoionization is a weak effect.
            If the effect is weak one would expect atmospheric gases to extend well beyond the ozone layer.

            “Oh and bow shock Logan we have touched on before. It is a ridiculous but often invoked mechanical concept. Those who go on about how low the density of the heliosphere is conveniently forget it when they want to. And they forget how small a proton is ( 10 power 22 protons in a gnat is a good way to think of it). The chances of any collision between particles influencing the boundary of coma are virtually non existent.”

            You seem to have ignored the fact that Lorentz forces play a significant role in the bow shock mechanism and is independent of the collision cross sections of particles.

          • logan says:

            Protons extremely punctual and electrons even more. The ‘hitting’ more probably performed by 67P’s escaping molecules.

            [At some point those two come together. Heliopause? ]

          • logan says:

            Electrons more probably deflected by molecular electron cloud. Protons more probably ‘going trough’.

            On general panorama this phenomena ‘decants’ an upper layer of lightweight electrons, while heavyweight protons slowed and absorbed* ‘deeper down’, trough several dozen kilometers.

            Here you have your dipole. Sort of.

          • logan says:

            This ‘decanting’ causes a very sharp electronic excess above, in the solar wind side. Also a very diffuse protonic excess below, in the coma.

            As in Terrestrial auroras, the excess protonic charge going all the way down, to 150-300 km from surface on Earth. To surface itself on 67P.

            67P is positively charged 🙂

          • harvey says:

            Bow shocks.

            Sorry the second link was supposed to be this one:
            http://www.scholarpedia.org/article/Collisionless_shock_wave

            There are some 300 papers in the literature mentioning ‘bow shock’ in the title which are astrophysical, & at least 30 with both ‘bow shock’ & ‘comet’ in the title; actually that will be a big underestimate as many use the name of the comet.
            Each has multiple authors, most with a PhD (some will be students.) I’d guess *at least* a hundred individual, qualified authors involved, all the papers in this database will be refereed. Also of course many conference presentations, opportunities to ask questions and argue.
            They contain both analytical models, computer models, & a wealth of data from comet fly-bys compared to the models. In fact they were a predicted phenomenon.

            Now of course the world believed in phlogiston once, but I rather think by now someone would have made his/her career by pulling the rug. And as it happens I have the math etc to examine it, & I see no fundamental problem.

            But, apparently I’m supposed to accept the unsupported assertion that this is all ridiculous, no formulae, no model, no comparison to data, no numbers, just an assertion.
            Now I have no data on the qualifications of those making the assertions; lets just say there is evidence their physics & especially math is….rather weak.

            Like much of pseudo science, there is a little core of reality in there. Double layers, Birkeland currents, sheaths etc, all exist, they exist & have importance in an astrophysical context. They are simple taken wildly out of context.

        • logan says:

          Thanks for the Reply, Harvey. Aren’t those ‘wave’ attributes?

          • harvey says:

            Sorry Logan its got a bit confused; which things have ‘wave attributes’?

            In physics, we *generally* reserve the use of the word ‘wave’ to phenomena which satisfy the ‘wave equation’. Whilst this is most often in vector form, which needs vector calculus, the simplest one dimensional scalar form is
            d^2u/dt^2=c^2 d^2u/dx^2 where c is the wave velocity.
            http://en.wikipedia.org/wiki/Wave_equation
            This can for example be derived (usually in vector form) from Maxwell’s equations to give the EM wave.

            This leads to a propagating disturbance we know as a ‘wave’, of the general type u(t,x)= exp(j(w.t+k.x))
            If its not a solution to that equation (& many, many things are!) we generally would not call it a wave. It leads to a dispersion relationship, basically how c depends on frequency, which is crucially important in the wave’s behavior via k(w). If k is real, the wave is not attenuated with distance, if it contains an imaginary part, it is.

            For a simple unattenuated wave
            k, frequency & velocity c are linked by
            k(w)=w/c
            wavelength= c/f
            w=2Pi.f (the ‘angular frequency’)

            ‘Evanescent waves’ are a rather special case you might come across
            http://en.wikipedia.org/wiki/Evanescent_wave

            Its too hard to do this here, just look up the wave equation, reams about it on the web! Aside from the more rigorous mathematical description, there are more ‘pictorial’ ones if that’s easier.

          • logan says:

            Hi Harvey. i am not a scientist. Could be saying just a bunch of non-sense 🙂

            Key issue here -as you say- is propagation. There isn’t. On static fields.

            But we are on relativity issues.

            Air-travel along a frozen ocean and we are seeing waves.

            Imagine a ‘static’ multi-spiral many dozen meters drawn in your parking lot. Set at the center and start spinning. You see ‘waves’ coming in, or out.

        • logan says:

          Hi OriginalJohn. Agree with you on photo-ionization not being enough. ROSETTA mission is fully prepared for this aspect of cometary activity and she is going to give us lot of knowledge.

          The impacting presumably occurs along several dozen [hundred?] kilometers. Why is improbable?

          Other plausible phenomena not discarded as far as energy budgets are not provided [Maybe not at this mission].

          Following with great interest every new clue contributed by the Teams and Out-Reach and also the following comments and contributions by all of You 🙂

          • harvey says:

            It is really not very meaningful to say photoionisation is ‘weak’ or ‘strong’ in isolation.

            There are two aspects to this.

            Firstly ‘weak’ or ‘strong’ *compared to what?
            In this case, compared to the interplanetary ion density, which, in absolute terms is really rather small, typically less than ten/cm^3. For comparison, there are ~2.7*10^19 neutral molecules/cc at one atmosphere 300K.

            I’m strong compared to a newborn; weak compared to an Olympic weightlifter; the former might be the closer analogy for interplanetary space 🙂

            Secondly, the rate of photion production depends on the product of three terms:
            the photoionisation cross section
            times
            the relevant photon flux
            times
            the target gas density.
            1. The first is a fixed property of the material (photon energy dependent.)
            2. The second increases as we approach the sun as a square law.
            3.The third increases dramatically as we approach the sun & the comet degasses..

            So out in the distant parts of the solar system I entirely agree; terms 2 & 3 are small, & photoionisation is negligble compared to background.
            Close to the sun, 2 & 3 increase dramatically, & photoionisation becomes a very strong effect indeed.

          • logan says:

            You are right Harvey: Personally is just a bet born of my expectation about important under-surface electric activity [on the micro level] 😉

    • Martin says:

      The singing comes from an interaction of the newly formed ions and the solar wind plasma and magnetic field. The paper explaining it is currently under review.

      • Kamal Lodaya says:

        Martin: Can I tease a little more out on this? The ion tail is also formed from an interaction of the newly formed ions and the solar wind. Can one expect the song to persist in some form in the tail, to an observable distance? As Harvey says below the effect is very weak, so let us say that if one had a spacecraft going through the tail (did Giotto do this?) behind the comet could it detect the song?

        Thanks, Kamal

    • Gerald says:

      Without warranty:
      If I understood it correctly, it’s interpreted as kind of a resonance effect sustained by an interaction of the comet with the interplanetary field, in some sense similar to string excitation by bowing.
      http://hyperphysics.phy-astr.gsu.edu/hbase/music/stringa.html#c2

      Since the observation is rather new, I’d expect, that it will take some more years until a fully satisfying answer is completed.

    • harvey says:

      The degassing material is photoionised by the sun, generating a tenuous plasma which is travelling through the interplanetary plasma & magnetic field, distorting it. There are also interactions with the solar wind. Instabilities in those processes give rise to the oscillations.
      However its important to realize this is a *very* tenuous plasma & a *very* low field. They measure ~2nT, for comparison earth’s field at the ground is ~50,000nT and even that is a ‘weak field’ in a technological sense; in the lab we routinely use fields to well over 10T (five thousand million times greater than 2nT) and far higher fields have been generated, especially for short pulses.

  • masanori says:

    Apart from this big finding of not being magnetised, what made me excited is Philae’s sharp bounce angle at the first touchdown.

    If my listening ability was enough, I think Dr Ulamec at EGU presentation suggested about the reason for this sharp angle bounce and told something like it might have been happened by subsurface slope. I thought/think that explains that bounce very well. But another thought came up to my mind:

    Is there really already no possibility that the harpoon actually did fire but “partially”, and happened to “kick” the surface towards unexpected direction??

    Sorry if already someone mentioned about this, as I don’t read many of previous comments.

  • logan says:

    Gas ‘blobs’, ‘waves’ and ‘jets’ are the most massive objects of the galaxy and surroundings. Would like to think they have precedence to gravity as ‘compactors’ of dust clouds.

  • logan says:

    Not only comets could be ‘layered’. Dust clouds could be, too.

  • logan says:

    ‘Decanting’ causes a very sharp electronic excess above, in the solar wind side. Also a very diffuse protonic excess below, in the coma.

    As in Terrestrial auroras, the excess protonic charge going all the way down, to 150-300 km from surface on Earth. To surface itself on 67P.

    67P is positively charged 🙂

    • logan says:

      This electronic excess at the solar wind side is rebalanced at the bow perimeter. Solar wind itself acts itself as an ‘infinite’ discharging pole.

      Not the case with the protonic excess. They go very deep, into that molecular ‘bubble’ [The coma]. They are protected, electrically isolated.

      How much do they travel before being stooped? Don’t know. But once stopped, those charges constitute the inner POSITIVE envelope of 67P core.

      The electric re-balance of that protonic excess is going to occur way down.

      Maybe along tails, and that is another ‘terra incognita’.

      ……………………..

      The core has charge ‘inertia’ and is always following up his inner POSITIVE gas envelope [by loosing electrons].

      Far, far away, When sublimation not being a relevant issue, envelope becomes a mere token, Then 67P core balances charge with solar wind [accepting electrons].

      • logan says:

        After perihelion, 67P’s orbital speed is going eventually to diminish. Also the strength of its ‘bow shock’.

        Also the ‘total protonic charge’ accumulated at that gas envelope. It’s field strength is going to equate strength of the more steady core. Negatively inducted surface charge is going to disappear at that [|those] moment[s].

        Nothing to ‘push up’ Solar UV freed electrons trough. So, they’ll enter an even more speculative ‘slow diffusing’ mode 😉

      • logan says:

        … And that could be a moment for electricity to show its beauty at surface.

    • logan says:

      Comets have an amazingly high amount of surface. Capacitance could go along.

    • logan says:

      This ‘loosing’ of electrons at 67P’s surface as it increases activity could start as a static charge accumulating at surface. There the charges could be ‘trailed up’ by dust departing.

      Don’t know if adding to this budget electrons freed by UV impacting at surface.

    • logan says:

      If adding freed by UV impacting electrons, Then we are seeing ‘a little more’ than dust at those jets 🙂

    • logan says:

      Those surface’s UV freed electrons quickly accelerated upward by the negative charge accumulation there. [Positive ions slowly going under]. Accelerated electrons making sublimating gas along its path to ‘glow’ 🙂

    • logan says:

      Of course, those departing electron paths are ‘affected’ by the ‘MAS’ magento-atmo-sphere.

  • logan says:

    Jets are auroras, literally 🙂

  • logan says:

    Easy physics clue:

    Radial-ism of jets should INCREASE the further they are from nucleus.

  • logan says:

    Another physic clue already contributed by SovereignSlave? is the iso- potenciality of the jets.

    http://blogs.esa.int/rosetta/2015/04/22/crescent-comet-cometwatch-15-and-16-april/

    • logan says:

      There is simple math to ‘ambient’ luminosity. If the light from those jets where just reflection from sun an surface on particle-o-sphere Then it wouldn’t diminish so quickly.

  • Robin Sherman says:

    Much as I have enjoyed the discussion above, this result makes one thing perfectly clear. The magnetic fields measured at the surface and and in orbit are rationally explained as being almost entirely due to interplanetary sources, the Solar Wind and the Solar Magnetic field.

    The corollary to that is the magnetic field due to magnetisation of materials in or around the comet is negligible. Moving electric charges in the vicinity of the comet, or a charged comet itself, would create a separate, measurable, magnetic field. Ergo the motion of electrically charged objects in the region between Philae and Rosetta at the time of these measurements is negligible. End of story. NO electric currents, surface gouging discharges or streams/jets of charged particles.

    The regions further out where photoionisation has been shown to be the primary vector for producing moving charged particles, interactions with the Solar Wind and Solar Magnetic field take place. Here, separate and measurable oscillating magnetic fields are found, the “singing comet”. To me this seems rational and consistent with results and measurements from other interplanetary bodies. The unknown is in the particular circumstances that produce this particular oscillation pattern, not how the magnetic fields are produced. As Harvey says that particular riddle may take some time to unravel, particularly as there are so many variables yet to be adequately constrained by in situ measurements.

    • harvey says:

      Agreed entirely.
      The only thing I would add is that the oscillation is unsurprising. Instabilities of this kind are commonplace in plasmas. The *detail*, full explanation, certainly requires much work.
      But the existence of such phenomena is routine.

    • THOMAS says:

      @ Robin Sherman

      “Moving electric charges in the vicinity of the comet, or a charged comet itself, would create a separate, measurable, magnetic field. Ergo the motion of electrically charged objects in the region between Philae and Rosetta at the time of these measurements is negligible. End of story. NO electric currents, surface gouging discharges or streams/jets of charged particles.”

      Perfectly true, Robin, if you are indeed speaking ONLY of “the region between Philae and Rosetta at the time of these measurements”. But you somehow give the impression of wanting to generalize this observation, as if you wished to claim that it demonstrates the absence of magnetic fields *anywhere* on the comet, at *any time*. That would be a logical fallacy of course, given the purely LOCAL nature of the data being presented. Particularly since the region where Philae landed then bounced three more times was presumably chosen precisely for its observed lack of “jetting” activity which could have endangered it.

      The spectacular jets constantly observed in the neck region since Rosetta arrived at the comet were over a kilometer away, so if they are indeed the result of electrical discharge activity, their associated magnetic fields could not possibly have been detected by Philae and Rosetta. A valid analogy would presumably be a 40KV overhead power line on Earth: even with this sort of power, if you take magnetic field measurements from 100 metres away, nothing will be detected and you might think the power had been switched off… The magnetic fields generated by electric currents are necessarily LOCAL.

      We still await the disclosure of the magnetic field data which ROSETTA has presumably also acquired in close proximity to the jets. (The detailed study of the properties of the jets must have been one of the absolute priorities of the mission, since the nature of the jets producing the coma of a comet have been the most intriguing, not to say enigmatic aspects of the behavior of comets since the first image of a comet nucleus (Halley) was acquired back in 1986).

      For the moment, AFAIK, rather strangely, nothing has yet been published by the ROSETTA mission scientists on the precise properties of the 67P jets, apart from the intriguing “700m/s” velocity announced immediately after ROSETTA’s arrival at the comet nearly 9 months ago.

      Far from being the “End of story” you seem to be claiming, the magnetic field data around the jets, once finally disclosed, will actually prove to be the start of a brand new chapter in our understanding of the forces at work in the Solar System and beyond.

      • harvey says:

        The analogy to a power line is quite simply wrong.
        Firstly the whole reason we use high voltage power lines is to reduce the current.

        But far more importantly, you have, crudely put, both live and neutral there; the current is going one way in one wire & the other way in another wire close by. (Actually its generally a 3 or 6 phase system, but the principle is the same.) In this case the two fields do cancel well at a distance large compared to the separation of the wires. That why we use ‘twisted pairs’, twin cables with L & N close together.

        Now we have *never* been given a coherent description of the ‘circuit’ in which these discharges are supposedly part. Sometimes it seems its just discharging a charged comet – numerically ridiculous – sometimes apparently its magically both an anode & a cathode at the same time, with electrons moving through an insulating comet without causing power dissipation we can see………….
        But for the ‘no field near a power line’ analogy to be correct, we need a ‘return connection’ to the comet carrying the same current in the opposite direction.
        Where is it? ‘Why’ is it?

      • sjastro says:

        “The spectacular jets constantly observed in the neck region since Rosetta arrived at the comet were over a kilometer away, so if they are indeed the result of electrical discharge activity, their associated magnetic fields could not possibly have been detected by Philae and Rosetta. A valid analogy would presumably be a 40KV overhead power line on Earth: even with this sort of power, if you take magnetic field measurements from 100 metres away, nothing will be detected and you might think the power had been switched off… The magnetic fields generated by electric currents are necessarily LOCAL.”

        A very poor analogy.
        A capacitor in a circuit would be a far more relevant example, after all an electric comet is an oversized capacitor which is being charged and discharged.

        What do you think happens when we place magnetometer across the insulator component of a discharging or charging capacitor.
        A magnetic field is registered despite the fact there is no current flowing through the insulator.
        So much then for the magnetic field being associated with a local current.

        Did I not mention on a previous occasion you should become acquainted with Maxwell’s equations.

        “…. (The detailed study of the properties of the jets must have been one of the absolute priorities of the mission, SINCE THE NATURE OF THE JETS PRODUCING THE COMA has been then most intriguing not to say enigmatic aspects of the behavior of comets since the first image of a comet nucleus (Halley) was acquired back in 1986)…..”

        Are you serious or do you actually mean “Since the nature of the jets PRODUCED BY the coma?

        “Far from being the “End of story” you seem to be claiming, the magnetic field data around the jets, once finally disclosed, will actually prove to be the start of a brand new chapter in our understanding of the forces at work in the Solar System and beyond.”

        “Argumentum ad Ingnoratiam” where a speculation is treated as a fact.

      • Kamal Lodaya says:

        Thomas: Let us turn things around and imagine that a magnetic field had been detected. What model would we use to understand what is going on? For example, recently lightning was seen at the eruption of the Calbuco volcano. Would one, therefore, conclude that volcanoes are powered by electric forces? How does that explain the processes seen on a volcano? I suspect the electric theorists would say that lightning is a complex mechanism not well understood by the standard theory and hence the electric explanation has to be the correct one. There are many complex things we do not understand, but making them mystical explanations of everything that is happening does not solve the problem.

      • ianw16 says:

        Thomas said:
        “Far from being the “End of story” you seem to be claiming, the magnetic field data around the jets, once finally disclosed, will actually prove to be the start of a brand new chapter in our understanding of the forces at work in the Solar System and beyond.”
        How do you know? Had advance notice of the results? Brave statement, given that there may be an ESA mission scientist sat there analysing these results right now, seeing these comments and saying to himself “Oh no they won’t!”
        Despite all its claims, EU has only one piece of evidence to so far bring to these discussions, and that an argument from pareidolia, i.e. “It looks like a rock.”
        Lenticular clouds look like UFOs, but I don’t go on meteorology websites claiming they are in, or about to be in, possession of evidence that these really are UFOs.
        I’ve always thought EU followers have a certain faith based behaviour in their attitude to anything (translate as everything) that shows their beliefs to be wrong.
        Now we can add the power of prophecy to this.

      • Harvey says:

        “The magnetic fields generated by electric currents are necessarily LOCAL.”
        B=u I/(2 Pi R).
        For an infinite conductor carrying a current I a distance R away. First year physics.
        The field decays as R^-1
        It is not local.

        • Robin Sherman says:

          Thanks for your comments Harvey. The measurements referred to took place from the time Philae left Rosetta to its final touchdown. A period of over 9 hours, or put another way covering three quarters of the comet and the volume of space enclosed by Rosetta’s orbit during that time. I specifically added the qualification to make it clear that I was not making a generalisation and indeed in the next paragraph stated that it did not apply to the whole region surrounding the comet. Generalisations are for speculation and theories, conclusions from experimental results require stated boundary conditions. As a practicing engineer/scientist I am sure Thomas is well aware of this. At no point did I claim this falsified EU theory either, that is an inference made by others for their own reasons.

          Arguments about the amount of Photoionisation are mute too as it is matter of public record, at the AGU and in the related publications, that the Rosetta science team have shown that the overwhelming source of charged particles in the areas of the comets coma measured up to that time, were due to photoionisation, specifically because of the forbidden transitions seen in electromagnetic spectra taken by the ALICE instrument. Further calculations carried out and detailed in the published articles, confirmed this by deriving the the levels of charged particles from impact cross sections and measured solar wind flux. These proved to be negligible compared to the actual measured charged particle densities. The other source of charged particles, those generated by collisions within the moving material of the coma, are of course a variable linked to the activity of the comet, but at the time of the published conclusions the density of the coma was such that this contribution was also deemed negligible compared to the levels resulting from Photoionisation. As Perihelion approaches that contribution will change and may become significant depending on how and where charge separation takes place as Logan and Kamal addressed.

          • harvey says:

            We do not appear to differ technically; its clear the data is currently consistent with photoionisation, & one publication said so explicitly.
            Off course the magnetic field data applies at the time & place it was taken. Over what range one can infer no significant current depends on what the current is supposed to be; which we are never told. But given the scale of the supposed discharges & inefficiency of discharges in moving neutral gas, a range of km is a conservative estimate.
            I know nothing of the profession or qualifications of those espousing EU views; however I would say the views expressed here by its adherents are utterly incompatible with being “a practicing engineer/scientist”.

    • logan says:

      Hi Robin. Needing energy well below a few hundred meters for cryo-volcanoes 🙂

  • logan says:

    A gigantic magnetic dampener. This document is simple and fun:

    http://scitation.aip.org/content/aip/journal/jap/117/18/10.1063/1.4919366

    “…the shield described in this manuscript is, to our knowledge, the by far strongest existing large-scale magnetic shield in terms of magnetic damping. In addition, its observed residual field, even with environmental distortions and built-in experimental hardware, is <1 nT.."

    • logan says:

      Thematic relevance being that magnetometer’s Terrestrial copies could be accurately calibrated in dampening chambers like this one.

Comments are closed.