Happy New Year!

We’re back! After a pause over the festive period to recharge our batteries (hoping that Philae will soon do the same), the Rosetta blog has now reopened for business. Welcome back to all of you!

Before we preview the exciting year ahead for Rosetta, we’d like to kindly remind you of some blog house rules:

  • Please keep all comments relevant to the blog post that you’re commenting on (repeated posting of similarly themed and irrelevant comments on multiple posts will be considered as spamming or trolling and will be trashed).
  • Please use respectful language when responding to other comments. If you disagree with something, that’s fine, but any comments that are considered aggressive or unnecessarily rude will not be published. Constructive criticism is welcome!
  • While speculation of what you see in the images is welcome (we, too, often speculate), please remember that confirmation of features, processes, etc., will only be provided in peer-reviewed papers, a process that often takes several weeks or months. As usual, we will report on any results presented in a peer-reviewed paper once they are published.
  • Comments including links to sites irrelevant to the post or to unpublished theories or non peer-reviewed papers will likely be trashed.

Many thanks for helping to make this blog an enthusiastic forum for interesting and relevant discussion and debate! And with that, let’s take a look at the year ahead (see next post!).

Wishing you all a very happy, healthy and prosperous 2015,

The Rosetta blog team



  • Jamie says:

    Happy New Year Rosetta team!
    You mention that Philae’s batteries are charging. Is this just an assumption or does the probe give a signal saying how much the batteries are charged. If so how many ‘bars’ does it currently have and when can we expect to hear from it again?

    • Harvey says:

      It says they *hope* they are recharging; not that they *are*.
      No new contact with Philae has been reported.
      Currently it will be using all the power available to warm the internal electronics, especially the batteries. Until they reach an adequate temperature, they will not charge.
      Estimates of when it might ‘wake up’ have varied wildly from as early as late January to as late as June. The absence of an *exact* location, enabling *precise* prediction of when its in sunlight, make this very uncertain. If its eventually found in OSIRIS images, the estimate should improve greatly in accuracy.

  • plata says:

    Will the comments for “Cometwatch – The Movie” be reopened? I’d still like to share my montages.

  • “[C]onfirmation of features, processes, etc., will only be provided in peer-reviewed papers, a process that often takes several weeks or months” – well, AFAIK exactly one peer-reviewed paper on Rosetta data obtained after arrival (which was exactly 5 months ago) has been published so far, the ROSINA study of D/H in the coma. I was told last November that a Nature special issue with many more papers – including OSIRIS hi-res imagery so far held back from the public eye – would come out “soon”: any hints when that will actually happen?

  • originalJohn says:

    Welcome back Emily. I hope you and your team are suitably refreshed. There is much to look forward to in the coming months including plenty of results from yourselves. It could be a momentous year.

    I see in your statement that you are rather preoccupied with peer review and publication with regard to theories and results. You should not be. When you are working at a frontier of knowledge, as indeed you are, you should not be unduly concerned with the peers. They represent existing and accepted knowledge which may of course be flawed, in which case peer acceptance would be a handicap. You may say that is the way of science but maybe that is why science is in a bit of trouble in many areas at this time, with surprise and incredulity expressed at every turn of the page.

    The Rosetta team need to be open minded and unbiased. The confident but unfounded expectation of hard packed snow for the lander should have taught them that. They need to consider all plausible alternative theories in their interpretations but mostly they need to present the raw data to the world and it will speak for itself.

    There is a general attitude in science in this era that we have all the answers to most things and we are just looking to tidy up a few loose ends, a rather arrogant and unjustified approach I am afraid and and not helpful in the quest for a true understanding of reality. The purpose of this Rosetta mission should not be to confirm existing beliefs. There have already been results at this early stage that should set a few alarm bells ringing and it will be interesting to see how things are dealt with as the journey of this comet progresses.

    • Prof Harvey Rutt says:

      The world wouldn’t have the faintest idea what to do with most of the ‘raw data’.
      It’s use requires detailed knowledge of the instrument design, pre launch calibrations, in flight calibrations and validations, removal of artefacts, nonlinearity etc etc.
      About the only ‘raw data’ which would be remotely understandable is the images; even those would be missleading without a lot of other input.
      CONSERT data would be especially difficult.
      Generally now science does require that the original data is eventually archived and accessible.
      But in practise, truly raw data will be a bit like much raw food; pretty indigestible.

      The lander team had to make assumptions based on the best knowledge at the time to design the system.

      Peer review is *not* about suppressing discordant results; it’s about removing errors; no decent editor is going to accept a referee’s rejection ‘because it doesn’t fit the standard model’, they will if, case in point from an earlier discussion, it points out dimensionally Inhomogeneous equations. It’s a quality check system, not some sort of closed Mafia as you imagine.

      • originalJohn says:

        Harvey, predictably your definition of raw with regard to the data is different from mine. In any event you underestimate the capabilities in the world. My definition would be the output of the instruments in recognised values or forms associated with those instruments, via the interface included for that transformation, as calibrated. No problem dealing with artifacts, non linearity etc etc.

        The Rosetta mission was launched in 2004 by which time there was evidence to suggest that comet nuclei are rock bodies. No evidence existed to suggest they might be hard packed snow. That was an invention of Whipple’s imagination.

        You choose the paranoid Mafia analogy. I neither implied nor imagine anything of the sort. It is not intent that filters out valid alternatives within the peer system. It is ignorance and preconditioning. It does not take much perception to see how a filter ostensibly as a quality control could effectively filter in other ways.

        • Prof Harvey Rutt says:

          That’s not ‘raw’ data; it’s processed data.
          The meaning of ‘raw data’ is clear; it’s the instrument output and associat d called gratification n etc files (both.)
          Certainly the wider community can do more with semi processed data, but some will probably then question the processing it’s already received.
          There is a spectrum.
          Images are relatively easy.
          Even, say, a mass-spec is not trivial; to interpret even that semi processed data, you need to understand the cracking patterns of the instrument; memory effects, the calibration data is complex. Few other than professional scientists could actually use it, but might stand some chance. Yes, I guess eventually it’s reasonable to give people access, but I seriously doubt anything useful will come of it.
          CONSERT is the other extreme. The semi processed data would itself be extremely difficult to make anything of at all. It’s not a simple pulse-time-delay system, it’s a PSK correlation system. I’m very sceptical anyone, and I include myself, could do anything with it.

          If it’s ‘rock’ where on earth do the vast quantities of water come from? There are multiple measurements on multiple commets by different techniques and teams of neutral H2O in the coma going back decades. We now have MIRO saying the same thing. In any case the measurements of OH are entirely convincing, and solar wind etc does not stand a moments review quantitatively, and is completely inconsistent with the behaviour of other bodies. Evidence of ‘hard packed snow’ specifically, no; evidence of water in some form in vast quantity, overwhelming. The craft then had to be designed from best guesses at the time.

          I entirely accept that you personally may not have a ‘conspiracy’ view, but others here have been absolutely explicit that they do. Every delay, etc is interpreted as ‘protecting the standard model’. In my experience science simply doesn’t work the way many here think. Decades ago, early in my career, there was a more ‘establishment’ attitude; now if you have a better interpretation, it will ‘out’ pretty quickly. Provided it’s real science that makes sense! The test is that, not that it fits some establishment model.

          • originalJohn says:

            Harvey, you are making a semantic issue about my use of the word raw and it is not important, except to you. Obviously releasing results as lines of binary code in isolation would be useless. The normal output interface of any instrument, whether it be graphical or some other form, is part of the instrument because without it the output would be unintelligible. It is a process but it does not change the values, therefore in my view it is still raw, just a different definition. Lets call it the raw results in an intelligible form. It is obvious that is what I meant.

            We have already discussed the likely origin of water in the heliosphere and I have told you that your numerical argument that there are insufficient protons to account for the observed water volumes (estimates at this stage) is invalid because you don’t know what the proton current density is in the vicinity of the comet. You have assumed a value that suits your argument. I have told you also that there are recognised effects in plasma that can increase the current density by many orders of magnitude and you have ignored that, to suit your argument. The interaction between incident protons and oxygen ions released from the rock is a plausible source of water in the coma. The generation of water from sublimation of non existent ice is not plausible, but promote it if you wish. I can add that the reactions within the coma itself between ions, neutral atoms and molecules are likely to be extremely complex and you know nothing about that either so anything you might say is selective speculation to support your argument. We can perhaps discuss this again in the future when further results are available.

            The consensus in science is very strong and difficult to break down. It is the way of science, that If most people support it it must be right. However that is not scientific. Truth has nothing to do with democracy. It is however difficult to escape the conditioning of your ( in an impersonal sense) education and the pressure of the consensus and remain truly objective, and why would you want to if it is your living, but that is the necessity. All valid arguments must be considered, exhaustively, and the consensus view must be continually questioned at every opportunity. In my view this has not been the case, at least for the last 15 or so years in several areas of science. Before that there seemed to be more open objectivity but perhaps that was an illusion. Anyway now we are in a situation of opportunity and the Rosetta scientists should take full advantage of it. The last thing they should worry about is peer approval.

            There have by the way been many pioneering scientists in the 20th century whose work has been virtually ignored or suppressed and I would name for example Nikola Tesla, Kristian Birkeland, Hannes Alfven and Halton Arp.

          • Harvey says:

            Its really rather pointless, because you dont ‘do numbers’ or consider real mechanisms.
            But the facts are that:
            – the quantities of water are a huge number of orders of magnitude too high for sputtering to be credible; no credible mechanism has been proposed to overcome that
            – thats partly because the sputter yield is very low
            – there are numerous observations of *neutral* H2O from multiple comets, including MIRO/67P, several comets, different methods, different instruments
            – if its sputtering oxygen in such quantities, it will have to sputter the other elements, mainly silicon, in similar quantity, & its not observed (*traces* of other sputtered elemets are easily observed; but not vast amounts of silicon.)
            – this mechanism should be operationg on many bodies exposed to the solar wind, not just comets, yet they dont have comas
            – the interaction between the solar wind, UV, & degassed species is indeed quite complex; but also fairly well (not completely) understood, & recent plasma results from Rosettta confirm it. Most of the required cross sections etc are well known from laboratory measurements.

            I’m ‘conditioned’ to look at the data. The results of doing that are crystal clear.

          • Gerald says:

            One may add, that stable water wouldn’t form from plasma at freeze-in temperatures of millions of Kelvins, just consider the repulsion of the atomic nuclei (protons and positively charged oxygen ions).

            The only way to do so would be at the very surface of the comet’s nucleus by proton implantation.
            But this would apply to silicon, too, forming e.g. silane (SiH4).
            Silane is volotile, but it hasn’t been detected togather with other volotiles of low boiling point.

          • Prof Harvey Rutt says:

            Gerald. You are absolutely correct that silicon would be sputtered off too, a point I’ve also made. But you would not get SiH4. At solar wind proton energies, it will mainly yield Si and ionised Si, and just possibly SiH (and ions.)
            Formation of SiH4 would be very difficult.
            The spectral signatures would stick out like a sore thumb.

  • Margarita says:

    Great to have you back, and I hope you all had an enjoyable and restful holiday break.
    Looking forward to sharing Rosetta’s journey with you during 2015!
    Best wishes

    • originalJohn says:

      Oh I do numbers Harvey but I also understand how they can be used selectively to promote a spurious argument. So in the absence of data I stick to plain language.

      As for mechanisms, the plasma effects I have referred to are well established and understood mechanisms. I choose not to name them or go into detail because I am not here to educate you. If you are interested you can investigate plasma behaviour for yourself. You will find that there are self inducing effects that can increase the ion flux by 20 orders of magnitude under some conditions, for example.

      What is the dust observed if it does not contain rock constituents principally silicon, ice dust ?

      And rather than asserting that the absence of a proton induced water “coma” around some planetary bodies shows that it cannot exist around comets, perhaps you should ask yourself what is different about comets that could account for the presence of a coma, and incidentally how is the coma retained by the nucleus.

      As I have said repeatedly there has never been a better opportunity to resolve these issues about comets than we have now. I am happy to wait for the results, particularly with regard to the precise composition of the jets near the surface of the nucleus, and also detailed mapping of the coma and changes in it over the coming months.

      • Prof Harvey Rutt says:

        So, please give us a numerically credible mechanism that generate huge quantities of neutral water molecules from the solar wind and rock – without producing a massive silicon signature, consistent with the Rosetta MIRO and plasma data, and measured cross sections etc. And consistent with the neutral water measurements on other comets, by different teams and instruments, decades ago. I have never yet seen numbers or formulae supporting these arguments; not one.

        No one is saying it is pure ice; it contains rock and organics; but solid rock, with a density of c0.4g/cc it most certainly cannot be. That rests on many months of detailed measurements, and is consistent with other comets, all low.

        No credible challenge to that density exists; ESA simply could not navigate, deliver Philae, if it was grossly wrong. The measurement is about as direct as it’s possible to conceive of for a comet; volume, and the gravitational force it exerts. F=G m1 m2/r^2
        Gravity has issues on huge scales, not on solar system scales, where (tiny, probably artifact, Voyager anomalies aside) there has never been evidence of an issue.

        • originalJohn says:

          Harvey, as you know the figure quoted widely for the water emission rate of the nucleus of comet 67P C-G was derived from the MIRO analysis by ESA(NASA) sometime in the middle of last year. That figure is e +25 water molecules per second. This would require 2. e +25 protons if the process of formation was proton bombardment of the rock surface of the nucleus resulting in combination of oxygen ions with protons.

          So, using the numbers in the ESA poster you linked in the blog, therefore assuming a proton density of 200 or 2. e +2 per cubic cm as typical of the general coma, and a solar current speed of 400 km/sec or 4. e +7 cm/sec, the number of protons impinging on each square cm of the surface of the nucleus is 8. e +9 per second.
          Assuming the projected area of the nucleus is 1 square kilometre or e +10 sq cm the number of protons that could uniformly impinge on the nucleus is 8 .e +19 or approx. e +20 per second.

          To fulfil the requirement the proton density must increase from 2. e +2 to 2. e +7 per cm cubed. An increase of this order is perfectly feasible in a moderate plasma pinch, as is evidently occurring at the surface of the nucleus, resulting from the Lorentz force acting on the filamentary plasma current.

          The pinch is indicated by the bright glow mode of the jets as opposed to the less bright, lower current glow in the coma and the dark mode elsewhere.

          • Harvey says:

            So, finally you agree the number of protons is orders of magnitude too small, & some mechanism is needed to ‘collect’ them over a vastly bigger area.

            The *solar wind* density is more like <10 BTW, you appear, again, to confuse the solar wind with the photoionised local plasma. So another factor of 20. I *think* a bow shock has already formed, it certainly will form, & then the comet is largely shielded from the solar wind anyway (some penetrates, you get some charge exchange etc with it.)

            On Halley etc orders of magnitude more *neutral water* was seen degassing, so the problems are even more acute.

            'perfectly feasible in a moderate plasma pinch'; of which there is absolutely no evidence from the magnetic field measurements of course, in the nT region; these are 5keV ish protons. There are *extensive* models of these magnetic field/plasma interactions, none show anything remotely like this.

            Sputter yields are *very* low; on a fresh surface you need several orders more to overcome that. So you'd have to argue it is in equilibrium, sputtering off previously implanted protons. Can we have some analysis of the kinetics of that?

            Even if you could collect the current, you won't form neutral H2O, which is copiously observed, and you must sputter of similasr amounts of silicon etc.which would show spectroscopically.

            How on earth does this current continue to flow? The sputter yield is small, the area 'illuminated' will rapidly charge up, just like an insulating sample in a SEM. Or is it not only rock, but conducting rock? Not common stuff.

            Why didnt Philae get blown appart? Why dont the RPG instruments show crazy results because the spacecraft potential is some massive value? Why isnt there all sorts of typical discharge noise all over the RF spectrum?

            Why arent all other rocky bodies exposed to the solar wind doing this, just comets? (yes, they *do* – on a minute scale, they dont pour out neutral water.)

            There would be a massive spectral signature from electronically excited species in the 'glow discharge' – which isnt seen.

            How about the H/D ratio? Have you checked the H/D solar wind ratio is *identical* to the mass-spec measured water H/D? It had better be.

            Aside from an orders-of-magnitude shortage of protons – now agreed it seems, with no credible way to remedy it, there are umpteen other issues.

            This will be my last post on this matter. If people are determined to believe it, no amount of evidence & physics is going to overturn it. In future I shall refrain from comment on all EU postings, it just takes up too much time & a rational discussion is impossible.

          • Gerald says:

            I’d accept 2 orders of magnitude increase of proton flux during an extreme CME. Still a factor of 1000 to fill in, which I can’t duplicate.
            Proton flux in CMEs e.g. here:

            Obvious correlation of outgassing with CMEs would support your hypothesis. Lack of this correlation would rather clearly rule out the hypothesis. As such, it’s at least a hypothesis which is testable,

    • origiinalJohn says:

      Gerald, the plasma temperature is probably not much more than 1 million Kelvin, and perhaps you would elaborate on what you mean by freeze-in.
      By the way oxygen ions are negatively charged.

      • Gerald says:

        The freeze-in temperature is the usual way to define temperature for solar wind, trying to get rid of the bulk velocity portion, see e.g. this paper:
        For oxygen ion – proton recombination, I’ve been referring to reactions within the plasma of the solar wind, where oxygen ions are charged positively.
        Neutral or negatively charged ions can only come from dust, cometary gas, or the cometary surface.
        But for (electrically neutral) gas, impacts by solar protons would immediately ionisize oxygen positively not just by the charge of the proton, but particularly by its high kinetic energy. So we’ve to look at dust and the very surface of the comet’s nucleus, which is accessible to solar protons.

        • originalJohn says:

          Thank you for the link Gerald. You were referring then to the rather special conditions in the solar corona and the plasma temperature there at which the density of excessively positively charged oxygen ions stops changing.
          The point of discussion was the conditions at the surface of the comet nucleus and the interaction between protons and oxygen ions originating from the rock.

      • originalJohn says:

        Thanks for the acknowledgement Gerald. Certainly the proton density would increase as a result of a CME. That correlation will be easier closer to perihelion when the arrival time is reduced. Increased nucleus activity coincident with CME s has been observed with recent comets. I well remember seeing such an event myself on the SOHO LASCO C3 image during the approach of comet ISON, indicated by an overall brightening.
        However there is no need to rely on CME s. The potential increase in current density in a plasma pinch is far greater, and the increase required in this instance is minor compared to the 25 orders of magnitude possible under some conditions. And there is nothing hypothetical about pinch effects. They are used extensively in fusion research. and represent the highest energy concentrations achievable, with any control.

        • Gerald says:

          The “pinch effect” is certainly possible under some specific conditions as e.g. in fusion reactors. But on the other hand, there are loads of data of the solar wind. These don’t show such an extreme enhancement in proton flux.
          I’d take this as a proof by contradistion (http://en.wikipedia.org/wiki/Proof_by_contradiction), that extreme pinching doesn’t take place in the solar wind with relevant probability.
          Consider, how difficult it is to build a fusion reactor. This is an indication, that these conditions don’t tend to form by chance.

  • Judy Hawkins says:

    I really appreciate your work keeping this forum focussed, it makes reading through the comments worth doing, and I’ve enjoyed following the on-topic links that people post.


  • LUIGI says:


  • Terran says:

    And Navcam images, from the other instrument teams there’s rather sparsely any information, which is understandable

  • Marco says:

    Hi Rosetta outreach team. The house rules appear to have expanded to disallow links to unpublished theories, etc. There are a couple of links, one to a photo metric demonstration of where Philae must be (outside of the supposed narrowed area, but it appears Philae is not there!?)
    The other is a link to overwhelming evidence that 67P has stretched into its current shape, rather than eroded or lobes collided.
    These represent very good citizen science and should be part of the conversation, even if they might embarrass the mission scientists by being a couple of steps ahead.

    • Harvey says:

      According to EU ‘theorists’, it is made out of rock.
      According to the ‘conventional community’, it is some sort of ice/dust/porosity composite, TBD.
      At the comet temperatures, both these materials undergo brittle fracture; they do not elognate significantly before they break.True ‘a fortiori’ of rock!
      Nobody’s theory has it made out of plasticine or bread dough.(which would also be brittle at comet temperatures>)

      How can it stretch to this shape if its rock etc?
      (Quite aside from stability & magnitude of the force arguments.)

      • originalJohn says:

        Harvey, one way the rock material of the nucleus could attain plasticity is by at some time being at a much higher temperature than it is now. It is established that this must have been the case with other comets from analysis of the mineral content of the nucleus eg Wild 2.

        • Prof Harvey Rutt says:

          If it stretched when plastic, why does it show supposedly matching features which must result from a brittle fracture? You can’t have your cake and eat it 🙂 if it was plastic when it stretched, why would it show sharp matching features?

          Somehow it had a plastic core, which kept it together, and and outer surface that underwent brittle fracture – (when the forces are far too small, and a constant angular momentum is stable against this mechanism.)

          It’s very easy to find apparent matches in two surfaces formed by similar processes. It would need a proper statistical analysis to show that the similarity had any significance. If the match in fact exists, we are a long way from a credible explanation.

          • Marco says:

            To answer your first two questions – I am not proposing that our physics is wrong – A plastic centre core and a brittle “mantle” is perfectly consistent with a variety of materials that we can model. There is no case to answer because the matching features is the observation side of this “science”. Philae’s bounce on Agilkia certainly indicated the outer is hard and brittle.

          • Marco says:

            It is NOT easy to find 3D matches in surfaces that are formed by the same process. Further images of the same area would look less and less like matches on every single new image. This is the case for things that look like faces, for instance. Coincidental matches are easily falsifiable.

      • THOMAS says:

        Hi Harvey,

        In my understanding of EU theory (I am no more an EU ‘theorist’ than you are a ‘dirty snowball’ theorist), cometary rock is not being *stretched*, it is being *eroded* by electric discharge machining. The two processes are utterly distinct.
        I’ve no idea what the “stretching” proponents think the comet is made of.

        But it would be nice if you didn’t lump all alternative models together into a senseless amalgam as a way of then attempting to discredit each one of them.

        • Harvey says:

          The whole point was that regardless of model, the material properties make no sense. There is no attempt to discredit *either* of them; simply to point out that *both* are inconsistent with stretching.
          Its hardly a secret I think ‘EU’ is mainly utter nonsense, nor that the ‘dirty snowball’ has plenty of issues to solve, but thats not at issue here. Purely whether ‘stretching’ makes sense.

      • Marco says:

        Hi Harvey, thank you for weighing in here. We really do not know the exact mix of compounds, nor their temperature, nor their state. You seem to be sucked in to the false dichotomy of rock or solid sublimating volatile rich porous mix. As you said in some comment somewhere regarding parsimony. Scientists should be all too happy for there to be evidence to decide what caused the duck shape without having to resort to Ockham’s razor. The supposed brittle or otherwise nature of the neck region is not evidence because we cannot measure that. Therefore, either we can prove it with photogrammetry, or we can’t. The photogrammetry is *science*, the strength of the interior to tensile forces is just idle speculation either way (The compressive strength of the neck is obviously enough to avoid collapse)

        Hopefully, this comment works.

        • Harvey says:

          The ‘photogrammetry’ is not science because it has no statistical validation; it rests purely on subjective visual matches. Its called ‘forensic’ – I’ve been an expert witness, it would get shredded in court. Subjective won’t do.Nothing at all has been ‘proved’.

          In the mean time;
          – the forces make no sense, they are too small for wet tissue paper
          – the stability argument makes no sense; if it started to stretch, its dendency to do so reduces
          – the fracture mechanism makes no sense; we need brittle fracture for matching fracture surfaces, but ductile behaviour for it to stretch but not break – *whatever* it’s made off, ice, rock or cream cheese 🙂
          The strength required to resist collapse is minute – & compressive strength & tensile strength wildly different, look at how stone masons build things.

          The ‘matches’ are sort of interesting; but they could very well be statistical chance, seeing what you want to see. If they are indeed real, some explanation has to be found for three other *serious* issues.
          Maybe, just maybe, one could come up with some sort of croque-en-bouche model with a brittle exterior & a gooey inside, but I still dont see how you get round the force & stability issues.
          So as I said a while back, maybe I’d keep it in as a very unlikey possibilty; but its got far more problems than the ablation & contact models – though they have problems too!
          I wouldnt be particularly surprised to see some completely new mechanism to form this shape emerge; nothing seems that satisfactory, let alone proven, right now.

          • Marco says:

            Hi Harvey, if you haven’t noted A.Cooper’s response below, it covers all your concerns and includes citations. I really don’t have anything to add to it.

  • emily says:

    Hi Marco,
    Discussion (including those with follow up links) on topical subjects are most welcome; the rule is to discourage spam links and repeated links to off-topic subjects.
    Best wishes,

  • Marco says:

    Thank you Emily, in that case, given that OSIRIS has come up with a blank on Philae, I re-offer the following photogrammetric evidence for the location quite a bit outside the diamond, but very convincing nonetheless:
    I wish that the mission scientists would check these citizen science efforts before dismissing them wholesale.

  • Marco says:

    And a particularly solid scientific collation of evidence on how 67P got its bi-lobed shapes. Photogrammetric evidence connects points on the head lobe with corresponding related mirror image points on the body lobe. The number of points and the exact distances associated with these points is a forensic proof. Again, I wish the mission scientists would check for themselves
    Before dismissing “stretch” theories for the shape of this comet and others.

  • emily says:

    Hi Marco, no problem, although maybe next time you might find a better discussion on a more relevant post on this blog :). By the way, you cannot say that mission scientists are dismissing any particular theory, because there are not yet any published papers on this topic!

  • Marco says:

    Hi Emily,
    I assume you are talking about the stretch theory and not the location of Philae for the moment.
    There has been several presentations at the #AGU14, and some published articles that specificially get input on this topic from the mission scientists. The article *implicitly* rules out stretch by not mentioning it as a possibility.
    Judge for yourself – I am sure they will retrospectively change their mind by the time they come up with a published research paper due to the weight of evidence….
    Anyhow – I shall keep it to topic – This is on topic checking to see whether the “housekeeping rules” have tightened.

  • originalJohn says:

    Emily, any chance of making the captcha things a little easier to read, or at least extending the time limit. There can’t be that many robots trying to post on here.

  • Prof Harvey Rutt says:

    There have been complaints about lack of ‘electrical’ data.
    Well, here are some.


    Densities, very low, pretty much as expected.
    ‘Consistent with local photo ionisation of cometary neutrals.’

    • origiinalJohn says:

      Thanks for link Harvey. Results on this poster are of little overall significance as they are a snapshot taken over a single period of a few days in Oct 2014 at an indeterminate orbital position somewhere in the coma ie where the craft was during the period, so at least several tens of kilometres from the nucleus. So they characterize the electron and unspecified ion densities in the vicinity of the hf transmitter/ reciever and the langmuir probes.
      Both ions (LAP) and electrons (MIP) ranged from zero to about 350 per cubic centimetre. Presumably the pulsing of the MIP data every 2 days represents periods when the instrument was activated whereas the langmuir probes were active for the whole of the test period.
      Not worth analysing this small window of results in detail but noticeable that the ions (not specified as anions or cations, but I assume cations) from the 13th to the 21st Oct had a sharp increase from a range of low-50 counts approx to 50 -220 counts approx. At this indeterminate position in the coma, remote from the surface of the nucleus both of these ranges exceed the 1 per cubic cm figure you originally assumed for protons.
      Interestingly in the panel where MIP electron density data is compared with COPS ( comet pressure sensor) data for neutrals (presumably atoms and molecules), they say, as you noted, “consistent with local photoionisation of cometary neutrals” ie what they were expecting. These are electron densities of 1-3 x 10 power 2 compared with neutral densities of 1-2 x 10 power 8. ie one millionth of the neutrals photoionised, not a very powerful effect at all.
      They have to do this at positions all over the coma including very close to the nucleus over a period of months before anything general and detailed can be concluded about ion densities. The global displays shown ( with no distance scale), and a projection of the nucleus surface are for electrons only.
      Finally the MIP measurements are based on a mutual impedance/ frequency relationship that requires an isotropic plasma. I hope this only means isotropic within the region of a single measurement because that is all that could be assumed.

      • Prof Harvey Rutt says:

        Now why am I not surprised they are ‘of little overall significance’?
        They are quite clearly entirely consistent with a straightforward, normal interpretation of this particular sample of space near the comet. Of course the neutrals are much higher; as his conclusions say, it’s consistent with photo ionisation. That’s what is expected.

        • origiinalJohn says:

          You are not surprised Harvey because you know I don’t agree with your minimialist proton argument.
          No comment on the fact that they are much higher than your original assumption?
          Do you think this one test fully describes the ion environment of a comet, in which case they can switch off and concentrate on other things. Do you think the ion density is uniform throughout the coma
          And you expected a photoionisation of one millionth of the neutral molecules ? Yet you asserted previously that it accounted for all the OH in the coma.

          • Prof Harvey Rutt says:

            They are not much higher; I used correct solar wind proton densities , typically <10/cm^3 in non-storm conditions. That is the high energy solar wind component., which it is as claimed was doing the sputtering. This refers to the photo ionised plasma, they are completely different things.

          • Prof Harvey Rutt says:

            Yes of course OH densities are expected to be way below neutral. It results from photo dissociation of the neutral H2O by hard solar UV. It’s not a particularly strong process; it’s important because the resulting OH emission bands are easy to measure. Direct measurement of neutral H2O is more difficult, although it has been done repeatedly.
            As he says, the plasma is consistent with this mechanism.

            At the moment, 67P will hardly be exposed to the solar wind at all; it is shielded by the photo ionised plasma and its bow shock etc. Further out, with little degassing and photo ionisation to form that plasma, it’s directly exposed.

            There simply are no surprises here at the basic level; it’s pretty much what one expects – detail oddities yes; gross disagreement with a degassing/photo ionised model, no.

          • originalJohn says:

            Depends Harvey on what you mean by not much. They are higher. You used an estimated average proton density for a particular distance and did not allow for any local non uniformities which are known to occur in plasma currents, and would be certain to occur in the heliospheric current sheet in the vicinity of a visiting body such as a comet.
            “This” refers to the density of unspecified ions at that position in the coma as measured by Langmuir probes. No way of telling if they are solar wind ions or the product of photoionisation.

  • A.Cooper says:

    Professor Harvey

    (in response to your objections to Marco’s and my stretch theory):

    Subjecting the proposed matches to a statistical analysis would indeed be a good thing to do. That sort of solid confirmation would be at one extreme of proof while your statement that it’s very easy to find apparent matches in two surfaces formed by similar processes is at the other extreme i.e. just random similarities here and there in random pairs between head lobe and body lobe- hardly proof at all.

    The question is, at what point does the weight of evidence of each apparent matching pair being followed sequentially along the ‘shear line’ by another and then another warrant the instigation of such a statistical analysis? By proposing one match between head lobe and body lobe, one is immediately constrained to match the next portion of the rim of the head to the next portion of the body- and in both directions around the shear line either side of the original proposed match. The chances of the next portions exhibiting matches as strong as the first match are very low. The chances of this process happening two dozen times over a 2-kilometre section of the shear line should at least raise the question of whether indeed we should be looking to perform a statistical analysis. 

    If furthermore, many of those matches have been confirmed in the third dimension using sideways viewpoints it should make the case for a statistical analysis all the more pressing. If having matched the head and body in both plan view and the third dimension we find that, by pure chance, surface ridges straddle the head and body lobe when they are fitted back together, it should make the case for statistical analysis absolutely sound. If having matched the lobes via these three methods you notice that they are matching along what were two subsurface strata ridges (in addition to the surface ridges) it makes the lack of any such statistical analysis a neglect of the scientific process. 

    You mention the forces are far too small to allow brittle fracture. You also mentioned in a response to Marco before Christmas (Updates From AGU; 18th December 2014) that the forces were too small. When referring to outgassing and stretch you said, “Firstly the forces are *extremely* small; they wouldn’t stretch wet tissue paper.” Marco was invoking the spin-up scenario whereby asymmetrical outgassing over decades, centuries or millenia could spin up (and spin down) the comet. You expressed doubt at this too: “Yes, gas jets etc can alter it, but it would take *vastly* bigger spin ups than those observed”. 

    Mottola et al (Sept 2014) have established a 20-minute decrease in rotational period (a spin-up) since 2009 alone and attribute it to asymmetrical outgassing. Seeing as the YORP effect is thought to spin up asteroids over millions of years to sub 2-hour rotation periods before they fly apart, it’s certainly conceivable that a process that works on a time frame several orders of magnitude lower will have ample opportunity to spin up the comet and then spin it down again. Possibly multiple times in its lifetime as a Jupiter-family comet. It follows that a large spin-up to a 2-hour rotation is conceivable and that it could then at least break apart or stretch if plastic enough to do so (see below). 

    You say that a constant angular momentum is stable against this mechanism. The angular momentum isn’t constant if asymmetrical outgassing is adding angular momentum either constantly or in pulses nearer perihelion. If you mean the rotation period would have a tendency to slow again during the stretch due to the conservation of AM, that’s true but it would already have stretched. Whilst in that newly stretched mode it would be awaiting the next AM input for the next spin-up and stretching phase. Although the period, omega, is an operating factor, so is r and the underlying factor is the tangential velocity of lobe centres/tips after each spin-up approaching and surpassing the orbital tangential speed for that r value. If stretch does indeed occur, this negative feedback of AM conservation assures a slow, controlled stretch working in opposition to tensile forces, not a flying apart which is actually a point in favour for spin-up. 

    My calculations for 67P were that a period of 90-120 minutes would overcome the acceleariton due to gravity along the rotation axis. This is in keeping with graphs of asteroid spin periods: the majority peak at around 6-10 hours, the numbers dropping away towards 2 hours. Then they drop precipitously at the two-hour mark, suggesting break-up when spun up to such high rotational rates.

     So we have a mechanism, asymmetrical outgassing, that could give sufficient spin-up for a break up. The only difference here is that we are concerned with what happens on the cusp of a potential break up and whether it always involves a clean break or whether it can involve a stretch. 

    Another way of inputting the necessary energy for stretch and without spin-up is a paleo Roche pass at Jupiter, altitude 120,000km +\- 10,000km i.e. through its rings. That’s beyond the scope of this comment but all explained in the link Marco left in his comment below and the 8 posts of the series (soon to be 9). 

    You say that if the match in fact exists we are a long way from a credible explanation. I presume you mean a credible mechanism for how the core could undergo a plastic stretch. If you mean a credible explanation for how two lobes could exhibit multiple matches after a statistical analysis and be a kilometre apart, the only explanation would be that they have stretched, regardless of the mechanism. So at that point the stretch theory would be proven at least within the error bars of the statistical analysis. The mechanism that brought about that stretch would be a separate but related issue. As Marco says “…we can prove it with photogrammetry or we can’t. The photogrammetry is science, the strength of the interior to tensile forces is just idle speculation either way.” The photogrammetry proves it or or doesn’t, regardless of the mechanism of the stretch. 

    As for the mechanism, Marco’s right, it is idle speculation at the moment but there are plenty of possible scenarios which would need further analysis and modelling but don’t, in principle, flout any physical laws. At the recent AAS 225 meeting, it was revealed that the comet surface was made up of 3-metre “dinosaur eggs” (see Science article link below). In that link it is said that marble-sized constituents were modelled and expected. These are still not ruled out as sub-constituents. Furthermore, at the same meeting it was revealed that the interior has a porosity of 74%. This means it’s conceivable that spin-up forces could cause brittle fractures in the pressure-sintered joins between the eggs/marbles in the interior. This would be followed immediately by longitudinal shearing of eggs/marbles over each other giving rise to frictional heating along their surfaces and not in their brittle interiors. This would concentrate all heat gain into the surfaces of the brittle components, a tiny proportion of the mass, meaning substantial temperature rises on those surfaces. This in turn would give rise to sublimation, the gases lubricating the movement still further. This would allow the stretching of an otherwise brittle comet. There would be no gases to lubricate the cosmic-ray-sintered casing, being spent of volatiles, so it would break with a brittle fracture leaving the shear-line matches and stretched neck we see today.

    The comment above by originalJohn re high temperatures in other comets e.g. Wild 2 chimes with the above scenario. 

    Perhaps the fracture would be brittle even further in towards the core. This still doesn’t preclude the differences in structure, pressure, temperature and composition bringing about a different response in the core. Robin Sherman’s cryovolacnism springs to mind and a link he left on the 14th December Cometwatch (below) shows quite a degree of perspicacity in the light of the subsequent ‘egg’ find. It refers to ‘firn’ which he suggested might be found in the core: small ice particles, only partially sintered, surrounded by sublimating gas lubricants. Yes, it’s Earth-based experiments but an interesting pointer with the temperatures being comparable.

    There are also multiple possibilities for shearing, torsion and flexion prior to ‘lift off’ of the head, generating immense amounts of heat in the interior. Indeed, the forward positioning of the head would have dictated that one, two or all of these forces would operate prior to the simplistic ‘upward’ lifting force plucking the head away neatly. Then there’s the tipping up of the sheared portion causing slow, relentless leverage in the core- along with yet more torsion and sideways flexion as the head lobe adjusted its position due to its new-found freedom in 8 of the 12 degrees of freedom (6 rotational; 2 translational). 

    And finally, there’s the further possibility that there were almost no brittle breaks around the shear line anyway! This would happen if sublimating gases were working their way through the very obvious fracture planes, preferentially, causing planar voids and allowing the uplifted portions to match to the body *as if* there had been brittle breaks. Indeed, the head appears to have lifted away from flat, bare fracture planes at its edges, the shear line, and there is evidence of outgassing along those planes prior to and/or during uplift. The only reason for the matches would then be that they were married at one time and were worked loose via planar void scouring (not pushed apart) at the centimetre scale, leaving the matching undulations at the metre scale and no associated detritus. What I would call a brittle break is the crystalline appearance, like broken marble, that you see around the back of site A and more spectacularly, further along the flanks of the body; not relatively smooth slabs that were once sandwiched, partially scoured out at their seam and then ‘levered’ apart like slate in a quarry- that is what the entire shear line looks like. 

    The possibilities are manifold. Speculation, yes, but like the matches, worthy of investigation. Which is why I’ve been looking for evidence of the massive outgassing that would have occurred at the shear line on the initial failure of the casing and gases from 700 metres inside the comet streamed out. That evidence is also documented in the series. 

    In conclusion, Marco and I don’t have all the answers but what we have found very much warrants further statistical analysis and in-depth investigation. 

    Citation links in support of the above:
    Dinosaur eggs:
    Twitter re 74% porosity (one of several)
    Stretch theory:

  • Harvey says:

    Lots of words; the problem is a complete lack of *numbers*, or *analysis*.
    You recognise the need for statistical validation that a match actually exists; but someone needs to *do* it; no one is going to expend a lot of effort until that test is passed.
    Wishful thinking is remarkably powerful, even when we try hard to be objective.

    Then there are three areas that need *numbers*, *analysis*.
    – Materials properties. Are there credible materials which *at credible temperatures* could do this? Far from obvious that there are – but it needs looking into.
    – Forces/rotation speed. *Do the sums*; the spin-up required is huge. Has any comet ever been observed with such a spin rate? Where does the angular momentum & energy come from? Where did it *go to* afterwards as it spun down to current values again? Since we have to assume this is ‘typical’ (other comets show this shape) some systematically operating, quantitatively credible mechanism is needed to spin it up & spin it down. (Whats actually stretched here is credibility 🙂 )
    – Stability. At constant angular momentum, the process is stable; the more it stretches, the less it tends to stretch. Now that *could* help (limiting the process) but it makes it hard to get started. But this needs proper analysis, not my quick back-of-envelope.

    Finally, how about timescales? How long would the surface ‘remember’ the fracture, the match remain visible, given the extent of surface remodelling on each orbit? How recently does this require the stretch to have occurred?
    You need a spin up/spin down on that timescale – & for it to be statistically likely we will see comets in that time interval, after up/down, before remodelling……

    If you want to be taken seriously, you need to address these issues *quantitaively*.
    Just saying well, if the current spin rate/force is too low, obviously it must have been spinning faster when it stretched’ doesnt cut it. You have to show that is quantitatively credible.

    I still suspect that the underlying mechanism causing the gross ‘duck shape’ may not yet have been thought of. Some ablative mechanism remains possible. Contact binary to me seems difficult to believe, but I’ve not reviewed the arguments in fine detail. ‘Stretch’. to me looks very improbable, lots of very difficult problems to overcome, but if the .matches’ are statistically significant, maybe.

    • Marco says:

      I think it is wishful thinking on your part that there is no match. The Prima facie evidence regarding actual distances and direction between matching points, and the number of sequential points is quite clear. Let us say that there is a 50-50 chance of a match happening in the same direction and distance from the previous one in a series on both lobes. For 12 matching points in a series that is a one in 2^12 that it is just a coincidence. I call that statistically significant, don’t you? That is also a very generous probability. Random ablation taken anywhere else on the comet would have less than one in 10 chance of a corresponding match a corresponding distance and direction to another random point a kilometre away. Are you really suggesting this or are you just assuming that we are making this up? Without actually checking the 12+ points yourself? It is quite a simple statistical calculation, even without knowing what process is causing the surface features. Suggest a process that would more preferentially than 50-50 have a coincidental match.

      • Gerald says:

        Hi Marco,
        I wished so much, that your suggested match would hold. And it’s indeed difficult to find 12 matching points. The chance is 1:4096 with the 50:50 assumption.
        The candidate is worth to be considered.
        But to be valid, it needs to go through some stricter tests.
        First the statistical argument: Considering a 100×100 grid of the nucleus, 10 scales, and 10 orientations, we get 100x100x10x10 = 1000,000 patterns to countercheck. With 12 50:50 points, that’s 1000,000 / 4096 = 244 expected random matches.
        Second: All perceivable features, which cannot be attributed to image noise, need a match. I didn’t find a match for the top-most part of the Civa image.
        Therefore I need several more arguments to be convinced, that the match is statistically significant.

        • Marco says:

          Hi Gerald,

          I think you are confusing the two separate photogrammetry exercises. The one regarding Philaes position and the CIVA images indeed requires several more arguments to be convinced that the given photogrammetry is statistically significant.

          The stretch theory, however, see scute1133site.wordpress.com, has several more arguments going for it in a very statistically significant sense. The reason is that the matches are constrained to be in precise intervals and in 3D mirror arrangement. Non-3D-mirrored matches can be argued to be more likely if the same process is etching the surface in different locations. Corollaries to the stretch theory is also able to explain many otherwise mysterious features of 67P.

          • Gerald says:

            Hi Marco,
            I just referred to the CIVA image matching. So I think we see this part similar.

            Regarding the stretch hypothesis, I’ve no final opinion. I’m currently preferring kind of run-away erosion and evaporation for the neck region, once the superficial crust has been broken at one location.
            I’ve been considering kind of break-uo like an egg with matching edges, very early after the first good NavCam images came in. This would get close to the stretch hypothesis. But after some closer inspection I didn’t find enough evidence to suggest this option, and think it’s more likely, that the matches are coincidental due to similar processes, which had been active before the run-away degradation started, leading to the neck we see by now.

            Persuing several hypotheses in parallel certainly makes sense, since the final solution should be able to definitively rule out all possible alternative explanations.
            This can only work together (meaning in competition) with proponents of alternatives.

          • Marco says:

            With regards to the matching features: It is actually very hard to visualise the situation in 3D to start with. Plus, because none of the features are yet named, it becomes very wordy to explain adequately. Thus, at first glance, it actually looks quite random and unrelated. Also, our eyes and brains are not geared up to visualise 2D images from different angles and shadowing into a 3D contour, which actually matches as a mirror image. *Coincidental* matches of this type has the feature of looking less and less like matches the more images are analysed of the same areas and more scaled measurements between points are estimated. This is not the case here, as more images are studied, the more measurements are confirmed and 3D shapes found to be interlocking and mirror matching in more places. Compare this to the “Face on Mars” hypothesis. Once more images were taken from different lighting and perspective, the less it looked like a face.

          • Gerald says:

            I can’t do this myself, but printing a 3D model of the nucleus resp. the suggested matchings should help deciding, how likely actual ,matchings are.
            Computer simulations with the digital 3D model may also do the job. But again, I can’t spend the time to do so, at least not in the near future. But that’s probably the best way to convince yourself and others of either of the two possible outcomes

            The comparison to the face on Mars only holds to some degree, since that has been a matter of illumination and the inclination of the human brain to perceive faces.
            The surface of the comet, particularly the edges, don’t change pretty much. So only the first few images add much new information about the structure.

            One difficulty with perception is, that once you think you see something, the brain filters out other information. That’s called selective perception:
            The only way I see at the moment to overcome this, is the proper 3D modelling as I suggested in the first paragraph of this post.

          • Marco says:

            Hi Gerald,
            A 3D model at the metre resolution in the areas concerned would certainly prove or falsify what we are demonstrating with image after image. The issue is similar to the face on Mars because we are perceiving a 3D shape with shadows to guide us. Different lighting even at the same resolution always clarifies more 3d details. Often, with 67P it takes several NavCam pictures of the same detail to be able to visualise it in 3D. Once you know where each peak and trough is, even if some are invisible in plan view due to overhead lighting, you can take measurements using the scale of the photo. It is tedious, but in the absence of 3D models, it is the only way to make progress in the meantime.

    • Marco says:

      Let me briefly look at the three areas,
      1)credible materials at credible temperatures. Let’s see, we know that it is likely that the material is an unknown composite mix of known materials. We don’t know the mix, the state, nor the starting temperature, nor how circumstances would change any of that. It is not hard to dismiss any proposed mix at any proposed temperature as a complete guess. What point is there to do numerical analysis on a complete guess?
      2)Forces/rotation speed. Comets would only be in a particularly fast spin rate for a very small time, while they are still roughly round and compact. The act of splitting or stretching would automatically slow the rotation due to the conservation of AM. if 67P suddenly collapsed to a spheroid shape, it would spin up by a factor of 4 maybe, just from its AM. A lot of AM is there to be seen from 67P. It changed quite considerably over just the last few years. There is plenty of anecdotal evidence that outgassing(and the YORP effect) is sufficient to account for the forces and required rotation speed.

      As far as surface remodelling is concerned, we are yet to see any surface changes anywhere on this comet.
      Parts of the comet that are completely devoid of volatiles and removed from active zones may conceivably remain unchanged for millions of years

      • Prof Harvey Rutt says:

        Do the sums; you need a heck of a lot more than a factor of four. And then you have to slow it down again.

        Of course you could look at credible materials; the temperature is an issue, most materials undergo brittle fracture at these temperatures; does anything credibly present actually behave in a ductile manner? Ice, rock, certainly don’t, it’s extremely unlikely a mix of two brittle materials will magically be ductile; dirty ice certainly isn’t (I used to climb extensively.)

        • Marco says:

          Hi Harvey,
          Slowing down is the easy bit. in fact, fast spin in objects of sizes down to small rocks and up to a planet is also the easy bit. I really don’t see the problem with spin up and spin down. We don’t know exactly how fast the comet needs to be spinning. We do know that Gravity has to be overcome somehow, which involves lower spin rates than we are talking about, and many comets, including this one have had their spin rates change much, much more than the YORP effect would indicate.

          All we really know about the composition of the comet is that it is black. I think that we are too conditioned with Earth like gravity and materials to think about how and what would react in this way in microgravity in space.

          • Prof Harvey Rutt says:

            Marco, you don’t see the problem because you don’t do the sums.
            The spin up needed is huge. Then, magically, you have to find a new set of jets that exactly reverse that. About all three axes.

            No, I don’t find the evidence visually compelling; I do see some vague, suggestive similarities, that’s all. But I know just how easy it is to ‘see’ such things in pictures.

            I *applaud* your efforts to do an analysis, but I don’t think it is correct. The problem is somewhat analogous to the old chestnut of ‘how many people in a room to get a 50% chance of two with the same birthday?’ Most people say 182 or thereabouts. Actually it is around 22. Each time you add a person, you increase the chance the next one will match.
            So we have a huge number of identifiable features, of many different kinds in the two images, formed by the same processes, and so generically similar in type and scale length. You pick a feature in picture A, and look for a match in B; if you don’t find one, you try again, until you do find a match. The question is is the number of matches significantly greater than random chance, given the inevitable similarity of the images in features and scale. They are not uncorrelated.

            I don’t actually know how one would do that sum, though I’d guess there are techniques.

            (Incidentally, I’m unclear if the two ‘matching images’ were appropriately adjusted for different angles of view and range; if not, any quantitative matches are highly suspect.)

            As I’ve said several times, I don’t rule it out, but it seems to have lots of problems. Probably more than ablation and contact binary, probably less than ‘electrical’ mechanisms 🙂
            I wouldn’t put a lot of money on any of them; I would be at all surprised if something completely new appeared.

          • Marco says:

            Hi Harvey, you say that features and their scale are not uncorrelated.
            How can features be correlated in mirror?

            The probablistic problem is nothing like the birthday/people in a room problem. It is more like a combination lock (or in the analog form a key and its keyhole) problem. How likely is it to find 12 points (be they peaks or valleys along a ridge or valley) where each point is roughly the same distance to its next point as the putative match, and the angle the point makes in space between the two adjoining points either side is roughly the same angle (but in mirror direction) to its putative match. To convert it to digital, you have a pile of combinations (sets of twelve consecutive points randomly on the comet) and a combination lock you are trying to match with those 12 digits (the putative mirror match reference points) How many combinations would you need on average to find a match?

          • Marco says:

            I don’t do the sums because I stand on the shoulders of giants like professor Rutt, who skilfully uses mathematics to disprove aspects of EU theory, and mr Cooper who uses mathematics to show how very feasible changes in AM can lead to gravity defying rotation speeds see below.

    • A.Cooper says:

      Harvey, here are my answers after each of your thoughts, quoted in sequence:

      Harvey says:
      12/01/2015 at 16:16

      “Lots of words”

      There were lots of words so as to cover completely all your objections to the extent that it would be pointless to bring them up again. 

      ” the problem is a complete lack of *numbers*, or *analysis*. Answered in my 3rd paragraph. 

      “You recognise the need for statistical validation that a match actually exists; but someone needs to *do* it; no one is going to expend a lot of effort until that test is passed.” Answered in my 3rd paragraph. If we had the software and the expertise to use it we would but having revealed very good evidence thus far, we are happy to leave it to those who are already well-versed in the use of that software and also to ESA scientists who are privy to the data from Rosetta that could corroborate the match via other methods (composition, surface density matches etc.)

      “Wishful thinking is remarkably powerful, even when we try hard to be objective.” Answered in 2nd and 3rd paragraphs. If you are still characterising this as wishful thinking in the face of the four methods by which matches have been cross-referenced then I doubt you’ve looked carefully at the evidence. However, you did say elsewhere that the matches were interesting. That would suggest you did give it some due thought and were thinking it was at least one notch up from wishful thinking. 

      “Then there are three areas that need *numbers*, *analysis*.
      – Materials properties. Are there credible materials which *at credible temperatures* could do this? Far from obvious that there are – but it needs looking into.” Answered, paragraphs 11-15. 

      “- Forces/rotation speed. *Do the sums*;” Done (paragraph 7). But see also, the correction below and reference to the head/body volumes which are currently useless for making really accurate spin rate calcs. That is why I did the “barbell” type approximation across the long axis which is as accurate as I can do with current info. It gives a maximum period for Marco’s spin-up and that is all one can derive with current information- although, it has to be reiterated that all these spin rates are doable via outgassing. 

      “the spin-up required is huge.” And doable via outgassing, ref Mottola et al, on a timescale that
      is orders of magnitude faster than YORP which uses photons spinning rocks at 3300kg/m^3 densities, not gases spinning comets at 475kg/m^3 densities. But this is largely a regurgitation of my paragraph 5. 

      ” Has any comet ever been observed with such a spin rate?” Probably not- see correction below

      ” Where does the angular momentum & energy come from?” Outgassing (answered paragraph 5).

      “Where did it *go to* afterwards as it spun down to current values again?” AM input is reversible, so by a commensurate amount of retro-outgassing.

      “Since we have to assume this is ‘typical’ (other comets show this shape) some systematically operating, quantitatively credible mechanism is needed to spin it up & spin it down. (Whats actually stretched here is credibility  )” This objection has now been answered multiple times and with barely a mention of the Jupiter Roche pass theory which doesn’t require spin-up anyway. In case you think that’s pie in the sky too you may want to read this first. Many chances for such a flyby. 


      “- Stability. At constant angular momentum, the process is stable; the more it stretches, the less it tends to stretch. Now that *could* help (limiting the process) but it makes it hard to get started. But this needs proper analysis, not my quick back-of-envelope.” On checking my calculation, I noticed that indeed it does fit on the back of an envelope so on this point you are quite correct, though I don’t see why it would make a case for disparaging it. That would be tantamount to disparaging angular momentum for being as simple as it is. But this is the correction referred to above: although the calculation itself is correct, I grabbed the omega value, radians per second, or rather its reciprocal, seconds per radian and converted it to minutes. I forgot to adjust it for rotation period. It was 90 minutes so that has to be timesed by 2pi, 6.284 making it ~9.5 hours across the long axis. So I apologise unreservedly to you and Marco for stating such a high spin rate (even though it’s doable via outgassing anyway). I’m sure Marco will be delighted and thank you heartily for making your back-of-the-envelope quip which prompted me to look. So Marco’s spin-up is now firmly on the table and has pushed my Jupiter Roche pass somewhat towards the edge. However, this was always the maximum period for spin-up being across the long axis of the stretched comet (as per my statement above on the barbell approximation and no accurate volume data).  Looking at the T^2:R^3 relationship, I think it will be more like 4-6 hours was needed when compressed back to its original form. All achievable through outgassing. We shall have to wait for fairly exact, separate mass values for head and body before that can be pinned down. The dimension values on this blog’s 67P stats page are across the longest distance in each dimension for each lobe and so don’t account for the big curvatures- useless for true volumes and therefore masses.

      The envelope calculation is:

      Gravitational constant: 6.674E-11 m^3kg^-1s-2
      Comet mass: 1E13 kg
      Radius based on long axis: 2700 m

      mRw^2= GMm/R^2
      so w^2=GM/R^3
      so w^2= (6.674E-11 x 1E13)/2700^3
      so w^2= 667.4/1.9683E10
      so w^2= 3.3907E-08
      so w= root 3.3907E-08
      so w= 1.8414E-04 radians per second
      so 1/w= 1/1.8414E-04 seconds per radian
      so 1/w= 5431 seconds per radian 
      which is 90.52 minutes per radian-figure given in error
      which is 90.52 x 6.284= 9.48 hours per rotation.

      If you zoom out small you might even fit that on a postage stamp 🙂

      “Finally, how about timescales? How long would the surface ‘remember’ the fracture, the match remain visible, given the extent of surface remodelling on each orbit?” Interesting as that may be, it doesn’t impact on stretch theory since any theorised conclusion that ran counter to preserving the matches we see would by its very nature be questionable in the face of actual evidence of the matches, if they are indeed validated statistically as having significance. I’d also concur with Marco’s point that areas spent of volatiles could remain unmodelled. 

      “How recently does this require the stretch to have occurred? You need a spin up/spin down on that timescale – & for it to be statistically likely we will see comets in that time interval, after up/down, before remodelling……” This is related to the last question and so I give the same answer. 

      “If you want to be taken seriously, you need to address these issues *quantitaively*.” I have done so as far as one can with the available data i.e. with the barbell approximation, and all rotation rates are doable within that envelope via outgassing. There isn’t sufficient volume data go any further at present. I’m sure ESA scientists have that at their fingertips. So, with that in mind, we can’t profess to rival 300 full-time ESA (and NASA/ Sandia) scientists who are privy to countless gigabytes of data that’s only just come in. What we can do is point to the strong evidence so far for a stretch, along with the calculations based on the information we have in the hope that these scientists will analyse the data in the light of stretch theory as well as the other theories. As it is, some are already force-fitting what they see to contact binary theory as was seen re some quite cringeworthy statements at AAS 225. This regarded the cracks in the neck being due to the head lobe crashing into the apparently ready-formed neck protruding from the body- and at the improbably low velocity of 3m/sec. 

      “Just saying well, if the current spin rate/force is too low, obviously it must have been spinning faster when it stretched’ doesnt cut it. You have to show that is quantitatively credible.” As I said above, this has been answered multiple times.

      “I still suspect that the underlying mechanism causing the gross ‘duck shape’ may not yet have been thought of. Some ablative mechanism remains possible. Contact binary to me seems difficult to believe, but I’ve not reviewed the arguments in fine detail. ‘Stretch’. to me looks very improbable, lots of very difficult problems to overcome, but if the .matches’ are statistically significant, maybe.” Thanks for keeping an open mind on it. 

      • Harvey says:

        Briefly, short of time.

        I dont see the relevance of that calculation; its not to do with cancelling the gravitational force; its to do with providing enough force to stretch the thing. Gravity is not relevant.
        To get a sensible stretching force needs far higher spin rates; then you have immense problems with spin up & magically spin right down to ear zero.

        Re match, you still miss my point.
        You are not allowing *for the intrinsic similarity of the surfaces*, formed by the same mechanisms.
        Firstly, we’d need to define what constitutes a ‘match’; how accurately do do matching vectors match quatitatively? A ‘match’ with a 10% tolerance may vanish at 1%; if its brittle fracture, surely it should be pretty exact.
        If you take two random patterns, matches will be rare; and rarer as you tighten tolerances; not difficult to calculate.
        At another extreme; two independly manufactiiured chess boards can easily be made to match everywhere; but they were never one item split down the middle.
        Natural systems (the Giants Causeway, drying mud, ripples on sand, things produced by diurnal or annual effect etc etc) often produces regular structures of characteristic scale. Its intermediate between chess boards & random.
        Somehow the analysis needs to allow for that systematic similarity. I dont know how to do that.

        The point about the stability is that the process tends to ‘stop itself’; the more it stretches, the less its inclined to stretch. That actually could help the argument, because it would tend to prevent it breaking under elastic stretch; but it might also tend to prevent it getting any distance at all.

        Sorry must go, just a quick response.
        Here there is a rational debate, unlike some other areas I have decided to ‘leave’.

        • Marco says:

          Hi Harvey,
          Gravity is *very* relevant. This is because the force is dependant on and proportional to the masses of the lobes. The “centrifugal” “force” is not a force so much as an acceleration, as is gravity. Thus, even with tiny accelerations, the force is the tiny acceleration multiplied by huge masses and acting on a neck much narrower and smaller than the lobes. I will leave it as an exercise to my more mathematical minded correspondents to work out the force per square metre on a simplified bi-lobed model with the rotation rate a mere 5% faster than what is required to overcome gravity. That pressure would tend to be transferred to the narrowest part of the neck, and that part might undergo liquefaction.

          • Gerald says:

            Say 100 N/m² as an order of magnitude estimate, untli there are more precise values.

          • Marco says:

            Certainly, a rubble pile of pebble sized, volatile rich rubble, held together via van der Waals forces between them but solid pebbles otherwise, would be much weaker to tensile forces than compressive forces. The force may appear tiny, but a loose pile of icy sand in space would not resist even that tiny force in tension, and may in fact behave more like a very viscous liquid under tension, due to the van der Waals forces, holding them together but allowing them to slide past each other, volatiles sublimating would lubricate the process. Movement of the lobes outwards would slow the tangential motion limiting the movement radially.

          • Harvey says:

            I’m sorry Marco, you are simply wrong here.

            You need a force big enough to stretch the neck.
            Gravity in this case is a *tiny* force operating in the oposite direction, but negligible.
            You need to spin it up enough to provide that stretching force; ‘cancelling gravity’ is just the first tiny component of this. You can ignore gravity for this calculation. Its ‘centrifugal force’ v strength of materials.
            Yes, I’ve done the sums, but Im fed up with always doing them; the spin up needed is huge.
            Then, magically, we have to spin it down again & arrive very close to zero; that would need a *mechanism* to arrive at (near) zero.

          • Marco says:

            What stretching force do you think is required? A stack of bricks in space doesn’t need much tensile force to pull them apart. Your “guess” about what is holding it “together” (actually holding it apart at this rotation rate) is as good as anybody else’s until there is a way we can find out. I don’t see why an icy pebble pile wouldn’t react in a away that is quite firm under compression, but will not even hold 100 N/ square metre under tension.

          • Gerald says:

            Hi Marco,

            a pile of pebble could probably be stretched, as you describe, and if forces would be applied appropriately.
            But there are two issues:
            – it would return to spherical after spin-down;
            – the shape on spin-uo wouldn’t be two lobes, but a buldge around the equator.

            That kind of simulations have already been done long ago.

            To get the observed shape, you would need to spin the body up to disruption, such that a ring forms outside the Roche limit. After some time you may get a binary, which then may form a contact binary.

            Here a more recent attempt:

          • Marco says:

            I might add that our earth based logic that perhaps “it’s strong enough to hold two huge masses apart without collapsing, therefore it has “strength of materials” to not stretch easily. In reality, due to the microgravity, there is a very small requirement on the strength of material to hold the lobes apart, and there is good reason to think that its resistance to stretch is way less than resistance to compression, and as you say gravity is virtually negligible in this sense anyway. I think it is a lack of imagination. You can’t imagine materials that would act this way based on Earth based experiments. This is not evidence, and even though C-P has sped up its rotation by in the order of 5% in a single orbit of the sun, you seem to think that it is the exception and that “huge” spin-ups are impossible. Huge spin ups are not only possible, but should be *expected* They are patently possible by this evidence, and it is very plausible that “huge” spin ups are not even required, based on a very porous pebble-pile model, which is plausible and matches density calculations and proposed comet formation theories.

          • Marco says:

            Hi Gerald, we are not talking about Modelling the whole complex beast that is the comet. Only seeing if there was plausible material that would react in a plastic way to the kind of gentle accelerations we are talking about. Models have to make a hell of a lot of assumptions. We don’t know which assumptions are right or wrong, and we don’t know which combinations of assumptions being wrong will make the most difference. The point of this argument was just about the neck material taken in isolation. Certainly, now that I am quite confident personally that it has stretched, a pre stretched comet appears to be hard and brittle in the mantle and crust, but ductile closer to the core.

        • Marco says:

          Regarding the supposed intrinsic similarity of surfaces. There are many features on 67P that are outwardly similar. We do not have a name for the different features, but there are various forms of “craters” “cliffs” spires and general peaks and valleys, as well as plains, boulders and dust. Importantly, there is quite a distribution of sizes, ie. scale to *each* of these. Correct me if I’m wrong. Thus there is correlation to be expected if we are comparing points on two of the same type of feature, albeit unlikely to be the same scale, but you could see a match plausibly between two “craters” on different parts of 67P if we ignore scale. However if we switch to “ridges”, there is virtually no general correlation between ridges generally, either in scale or shape. We are talking about many consecutive points on a ridge matching, and when we continue following the ridge, and nearby *constrained* points, the matches keep mounting. It started out as 12 sequential points on a ridge which were the most obvious starting matches, and has continued to over two dozen similarly matching points, with continuing other unrelated but corroborating evidence which just on their own would be compelling and statistically significant.

        • Marco says:

          Talking about defying gravity, one calculation a few months ago tipped me off on an alignment which will defy gravity, albeit in a pulsating, radially dependent way. What tipped me off was the calculation of the Lagrangian L1 and L2 points for Rosetta cf the sun and 67P. I was surprised to hear that the points were somewhat within the comet nucleus! The corollary to this is that when the rotation plane of 67P aligns with the sun, gravity will be overcome twice each orbit at the lobe extremities. Thus boulders will jump, dust will scatter, and the comet may experience tensile forces radially and may even transfer to the neck.

          • Gerald says:

            My back-of-an-envelope calculation for L1 and L2 returns more than 200 km away from the nucleus (178 km at 1 a.u. = 150,000,000 km from the Sun).
            I’ve used M2=1e13 kg for 67P, M1= 2e30 kg for the solar mass, and
            R * (M2 / (3 * M1))^(1/3) as estimate for the L1 distance. L2 distance is about the same. Both are about the Hill radius.


          • Marco says:

            Oddly, I had asked about the L1 and L2 points back in August, thinking that L1 may be an advantageous point to park, being able to see the day side of the comet, especially on approach. Also, later in the mission, to conserve orbital adjustment fuel for an extended mission perhaps over past aphelion or over a second perihelion.
            At that time, in August, someone had mentioned (and nobody corrected) a calculation of L1 and L2 to be inside the comet. This appears to be completely wrong. However, the sum of centrifugal forces and tidal forces may still be greater than gravity at the extremities of the head and tail. Duck synchronous orbit is less than a handful of kilometres above the extremities.

          • Gerald says:

            I guess, those calculations referred to the Lagrangian points of the nucleus itself, interpreted as a binary, not to the comet – Sun Lagrangian points.

          • Gerald says:

            As far as I know, gravity wins over inertial pseudoforces everywhere on the surface of the nucleus.

            Synchronous orbits shouldn’t be far away from the nucleus. I didn’t calvulate it, but I guess, it’s less than 30 km from the center. (Centrifugal pseudoforce is proportional to the radius.)
            (Take 4 pi r² / T² for the centripetal acceleration, and compare it with the gravity G m/ r² at distance r from a point mass, with G the constant of gravity, m the mass of the comet, and T = 12.4 hours the rotation period of the nucleus (convert it in seconds); the mass of the satellite cancels out)


          • Gerald says:

            4 r pi² / T²
            Hope this time I’ve hit the proper keys.

          • Marco says:

            I haven’t worked it out, quite, but I believe the sum of centrifugal force and tidal force should overcome gravity when the lobes are aligned with the sun, at the extremities., at about 1.6 AU from the sun, in May 2015.

          • Harvey says:

            I have a nasty feeling *I* got the Lagrange point wrong, in which case apologies. I didn’t write the calculation in my day-book as far as I can see as it was casual.
            I rather think that I missed the *cube* root in a small font display, & used *square* root in error. As the argument of the root is dimensionless, thats not immediately obviously wrong, a dimensional check still works.
            However note that 67P’s gravity is so weak orbits anywhere out towards the Hill radius, & the Lagrange point locations, will be extremely unstable towards very slight perturbations. This is why Rosetta uses ‘active’ (triangular) ‘orbits’ even at 30km, or certainly was doing, not checked recently.

          • Gerald says:

            Hi Marco,

            you’ve to go near the Roche limit of the Sun to get tidal forces strong enough to overcome the gravity of the comet.
            That’s less than about twice the diameter of the Sun, i.e. less than 1/50 a.u., inclusive considering shape of the comet, and density quotient, and taking the fluid model as upper bound of the Roche limit.

            Sun grazers can be destroyed by tidal forces.

            Centrifugal forces are only a fraction of the gravity on the comet’s surface, far less than 50%. At a density of about 100 kg/m³ for the comet, gravity and centrifugal force could have become similar for 67P; previous density estimates of the comet had been such low, but have been revised.

          • Marco says:

            Hi Gerald, I do understand Roche passes and I fully realise that the tidal force is tiny compared to the gravitational force, and that the centrifugal force is significant but only cuts the gravity in the order of a half at the extremities. However, even though Earths tide is a tiny percentage of its gravity, it has very visible effects. I was first finding out the scale of the tide at the comet, however small, and whether and what effects it could have due to “spring tides” in May.

          • Gerald says:

            Don’t take the 50% too literal; it’s probably even less, maybe roughly 10%. But I’m not sure where exactly the correct number is. It’s just safe to say, that it’s less than 50%, to be sure, that small tidal effects cannot disrupt parts of the surface.

            Some tidal effect should be possible, yes, but it won’t reshape the comet. It might act on the dust environment. I don’t know the ratio of the tidal forces within the dust environent relative to the pressure by outgassing, solar wind and uv radiation. Tides by Sun’s gravity might get relevant for slow-moving larger grains the closer they get to the Hill radius; I can’t easily quantify that.

          • Gerald says:

            Hi Marco, the numbers for ratio of centrifugal force to the surface gravity have been released:
            “The centrifugal force varies from negligible to one-third of the gravitational force.”
            Reference: http://www.sciencemag.org/content/347/6220/aaa1044.full

          • Marco says:

            There are two ways such a “small” tidal effect can make an actual difference. If there is liquid in the comet (evidence from stardust supports it, and panspermia proponents do also) the tidal effects will affect the migration through such a porous structure. The other way, assuming a rigid solid superstructure, that may have weak spots, the “flexion” of the increased amplitude at alignment in April/May of the tidal acceleration will effect a diurnal rocking motion, similar to that of a skyscraper due to the day/ night differential of temperature, but with a structure of a comet that is far less resistant to tensile forces than compressive forces.

          • Gerald says:

            Viscosity of liquids (at the relvant temperature range, to rule out helium ii) is too high to be influenced in a non-negligible way in pores by the considered tidal forces.

            I didn’t check to which degree flexure could be possible in some settings.

            Thermal “tides” by diurnal insolation oscillation look more reasonable, leading to thermal stress near the surface.

  • A.Cooper says:


    I agree that there’s rational debate here as exemplified by your sticking to the relevance of the calculation rather than dismissing it on the ground that I’d given the wrong answer before. Many would throw the baby out with the bathwater. You are questioning the legitimacy of the baby in the first place which certainly is  sign of rational debate (although, of course, I disagree). 

    I shall contribute more later. Like you, I’m a little short on time. 

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