Interpreting images – more on how the comet got its shape

On 28 September, a scientific paper was published in Nature, presenting a view on the formation scenario of Comet 67P/Churyumov-Gerasimenko, based on Rosetta OSIRIS images (read our news report here). The paper, led by Dr Matteo Massironi of the University of Padova, Italy, evaluated two possible models to explain the comet’s curious shape: the merging of two cometesimals or the erosion of a single object. Observational data and thorough analysis of the comet’s gravity field pointed towards the first of the two hypotheses: 67P/C-G seems to have originated from two separately formed comets that merged at low speed.

The topic has generated a lot of discussion in the comments thread of this blog, in particular by proponents of an alternative explanation put forward by our blog readers Marco and A. Cooper who suggest that the comet was once a single body that has since been stretched into two separate lobes.

We asked Matteo to share his opinion not only on this subject but also on the general topic of how planetary images are interpreted in order to arrive at a robust scientific theory.

Here is what he wrote:

Sorry for my late reply, but I wanted some time to go through the blog where the stretching hypothesis is described before saying something about the supporting geological proofs. As a scientist, I do not normally read works that have not been rigorously reviewed and published in scientific journals. Probably that is my fault and I want to thank ESA to have created this interesting blog allowing so many people to be an active part of Rosetta’s discoveries.

As a geologist, I would first like to point out some basic principles to follow when dealing with space images for geological interpretations. I believe these suggestions could be of some help to anyone who is going to submit his or her own work on cometary geology and structure.

These principles can be synthetized as follows:

  • Be a good field geologist
  • Be rigorous
  • Never fall in love with theories (particularly your own ones)
  • Be short

1) Be a good field geologist
Whenever we observe a geological landscape we filter it on the basis of our own experience. Becoming a good field geologist is a hard task because it requires the combination of a deep knowledge of geological processes and a large amount of direct experience. I normally spend half of my time working on Earth geology and doing science based on field geology. Indeed, working in the field deeply increases your skills in correctly recognising geological features (tectonic, volcanic, glacial etc.). If you are not able to recognize different geological features you might fall into common perceptive traps by, for example, perceiving continuous illusory lines linking different unrelated geological objects.

You might like to enhance your own geological experience by stepping back from your laptop or work-station, leave 67P/C-G images where they are, wear a good couple of boots, have a walk and reach a panoramic view where rocks are beautifully exposed. Since Comet 67P/C-G displays layered material, you should choose a good exposure of a well-stratified sedimentary succession or a heavily foliated metamorphic sequence. Once you have reached your observational point, sit down, take a breath and start drawing what you see.

You should at this point be able to recognise different features: the primary ones, which are strata and foliations, the secondary ones, that can be faults and fractures, and the morphology which in your sketch is the line separating the sky from the landscape. Most probably you will see that the morphology might in places follow the primary structures, in other parts the secondary structures and in many others it simply follows his own shape given by erosional processes. Any matching exercise in geology should take into account only primary and secondary structures, while the morphological ones, if not related to the previous ones, should be avoided.

For example, restoring a faulted and sheared geological section should be based in collimating the primary structure after having recognised the faults where shear took place. The surface morphology should be avoided because it is affected by later erosional processes, which in any case on Earth are often much less relevant with respect to the ones happening on comets.

In substance, we cannot rely on the morphology of a heavily changing body such as a comet, but only on the expressions of its internal structural features.

In any case, after your panoramic drawing is completed, please walk into your panorama and see if what you have interpreted is correct (it would be better to be accompanied by a field geologist). After this simple exercise, come back to your work-station and try again to interpret the comet images from Rosetta. You will probably find something different than what you first thought.

2) Be rigorous
Any time I work on planetary images, I need correctly scaled and calibrated data that can be overlapped onto Digital Elevation Models or Shape models. In this way, I know perfectly what the possible errors are on my geo-structural interpretation. The Rosetta-OSIRIS team is really smart on these procedures and many people from MPI, DLR and LAM are involved in image calibration and shape model realisation (applying different methodologies). Hence, for example, I know that the error in the estimate of angular deviation from perpendicular between the strata and the local gravity vector is on average of 2° and in the worst case of 4°. In any case, my point is that any promising observation deserves a thorough and detailed investigation to understand the possible errors.

My advice “be rigorous” also means to go deeply through any published works before critically judging it.

3) Never fall in love with theories (particularly your own)
In general, science works from observations to hypotheses to models to theories. An observation may trigger a hypothesis, which should be tested with different approaches trying to find evidences that might undermine your own hypothesis.

For example, neck-enhanced erosion and simple contact binary of two young cometisimals were the two favoured scenarios for Comet 67P/C-G’s formation because they do not present any problems to existing theories related to Solar System formation and evolution. On the contrary, a contact binary of two fully-formed comets with an ordered onion-like inner structure raises relevant issues with pre-existing models (already correctly highlighted by some readers of this blog in the comment section).

In my opinion, these issues can be synthesized as follows: i) understanding how strata can form in the primordial Solar System, ii) how a comet might avoid any catastrophic collision during their lives, and iii) how low collisional impacts can happen in the primordial proto-planetary disk. The only issue that was already solved is the formation and stitching of contact binaries through low velocity collisions (see the publication The shape and structure of cometary nuclei as a result of low-velocity accretion by Jutzi & Asphaug for more information).

Due to the controversial implications that the onion-like contact binary raises, we tried to find other lines of evidence that might undermine what was apparent from the former observations. This is why, from the best fitting planes, we passed to the geological sections and afterwards worked on the angular relationships between strata and the local gravity vectors. All these independent observations based on primary structures support the view in which the comet derives from a contact binary of two comets with an onion-like interior.

Our cometary mission is called Rosetta because it has the potential to decipher the origin and evolution of the Solar System. We should put aside our previous theories and models and try to study images without forcing our observations to a particular model or another. Theories and new models will come later (stay tuned!).

4) Be short
When presenting your theories it is important to be short and concise – more words do not necessarily make a scientific hypothesis stronger.


With those points in mind, and after spending some time familiarising myself with the stretch hypothesis of Mr Cooper, and with the comments posted on the original thread, I have the following remarks:

-It seems that most of Mr Cooper’s observations are based on surface morphology with many primary and secondary features not correctly recognized (see point 1 above for advice on geological interpretation)

-He begins explaining the stretching hypothesis, providing the observations that should support his theory only afterwards. In general, science works the other way around, from observations to hypotheses to models to theories (see point 3 above). On the contrary, his observations in support of the stretching hypothesis are only based on putative matching points recognised on the surface morphology. Something else is really needed to corroborate the hypothesis.

-Some other blog readers and commenters have asserted that matching is enough and probably the same was for Alfred Wegener’s description of continental drifting and the later plate tectonics theories. In fact, this is not correct: even Wegener provided many independent lines of evidence including geodetic, geologic, geophysics, paleontological and paleo-climatic arguments. And the same was for plate tectonic, with additional paleo-magnetic and geostructural evidences.

– Relevant suggestions from the general public are valuable to scientists, but please take your time to become familiar with the supporting scientific literature before immediately arriving at a different conclusion.

– If anyone wants to submit a scientific paper on the stretching hypothesis (or any other topic!) please keep in mind the points above about geology, rigour and providing convincing evidence in a concise way.

Best wishes,



  • Gerald says:

    A big THANKS for spending some of your precious time for explaining these – particularly methodological – clarifications!

    • Marco Parigi says:

      Gerald’s question.
      “Hi Marco,
      in case the other post has been swallowed, here the short version:
      Why haven’t the presumed chemicals of the presumed liquid interior been observed during the outbursts?”

      This is because I have been postulating liquid water as the major species responsible for the BLEVEs.

      With the other detected species of dust, etc. as a suspended mud in the liquid water compartment..

      • Gerald says:

        Hi Marco,
        oh sorry, I remembered you postulating hydrocarbons of small molecular weight, like C2H6.
        Liquid water needs higher pressure to stay liquid, then usually near 0°C.
        A BLEVE would be benign near the triple point, since most of the water would just freeze when reducing pressure.

        Large amounts of liquid water in the deep interior of the comet aren’t compatible with e.g. the presence of poorly water-soluble supervolatiles like CO, but also with the temperature of the interior of the comet, where water can only exist as ices (includig clathrates).

        • Marco Parigi says:

          Hi Gerald,

          The chemical signature coincident with the Anuket outburst is consistent with a BLEVE in which water was the main constituent. Minor constituent volatiles went up in proportion to water. Of course, absolute volatile concentrations would help narrow that down, and I await the peer reviewed paper….

          • Marco Parigi says:

            Gerald, you say,
            “..Its inferred from observations, measurements, and physics.
            Even the most direct measurements are inferences, at the end, derived from instrument counts/voltages and instrument calibration, from data received via radio waves and receiving antenna, software compression and decompression, etc.”
            There is not a single one of these things that I am disputing. The observations, measurements and physics fit with the stretch paradigm, as well as the warm soft core paradigm which I am also hypothesising.

            The only thing I am disputing is the way the inferences are made based on the axioms inherent with the Whipple model. If one of the axioms is that all the volatiles are solid in the interior of the nucleus, no amount of logic based on that axiom or exterior measurements is going to give a contradiction directly. It will just fail to predict new facts, such as the failures to predict onion layers, or the abundance of O2, etc. The number of failed predictions are myriad. There is a multiplication of accretion disk parameters required to fit these failed predictions in. With enough parameters, one can fit a camel. My paradigm(s) require interpretation of these measurements as evidence of 67P’s very recent history, not arbitrary formation scenarios that are untestable.

        • Marco Parigi says:

          Hi Gerald,

          Like I have said previously, since we do not have a thermometer that can go deeper than a few centimetres, using the assumed interior temperature to disprove liquid water as the source of the outburst begs the question. If I didn’t believe the internal temperatures (at a point 50 m or so below the surface) and pressures could keep water liquid, I wouldn’t believe they could be the source of the outbursts as a BLEVE.

          The outburst in question involves a lot of stored pressure breached on a relatively small part of the surface. If I was engineering such an outburst, liquid water (mud) would be so much easier than supervolatiles in a chamber.

          • Gerald says:

            Hi Marco,
            I’ve no problem with constructing that behaviour technically (as a thought experiment).
            I just can’t see it occurring naturally without violating several reasonable – if not evident – properties of the comet and its likely environment the last few billion years.

          • Marco Parigi says:

            Hi Gerald,

            The key phrase you use here is “Not evident”.
            Reasonable properties are not necessarily backed by the rigour associated with science.

            For instance, Geocentrism is perfectly reasonable in the same way, just not evident in terms of solar system bodies.

            Reasonableness is subjective, and cometary science seems to have assumed objective properties onto things like internal temperature, cometary history, and related phenomena that have really only been decided by consensus and have not been “tested”, asked to be proven or predicted any new facts. Reasonable internal temperature has been decided by consensus – not by anything we could measure or observe directly.

          • Gerald says:

            Hi Marco,
            besides direct observation and “consensus”, there is something in-between: inference, indirect evidence, based on observation and calculation.
            Some inference methods are statistical in nature, hence not perfectly water-proof.
            But the road beween “not perfectly water-proof” and “evidently false” is long.
            The temperature in the core of the comet e.g. isn’t known by direct observation. But there is indirect evidence of “the” temperature being low, maybe a few 10s of Kelvins.
            From the observation of supervolatiles their presence – either as clathrates or as ices – is rather straightforward, since otherwise higher internal pressure would likely disrupt the comet, hence low temperature.
            By calculating the flow of radiogenic heat it’s likely, too, that the comet is cold in the core. It’s size is too small to keep this heat for sufficiently long for any relevant warming. (That’s in contrast to the much larger (dwarf) planet Pluto, where radiogenic heat isn’t negligible).
            Solar heat is insufficient for an object in the Kuiper belt to heat up. The comet (particularly the supervolatiles near its surface) wouldn’t have survived for long enough in the inner solar system to allow for heat transport into the deep interior. Besides this the supervolatiles would have shielded the interior from warming.

            To overcome the arguments for a cold interior of the comet you need very sophisticated mechanisms, which are exceedingly unlikely to occur naturally.

            In absence of convincing observations (the interpretations regarding stretch don’t look convincing to me so far, for several reasons), there is no useful hint to question the “consensus” inference of a cold cometary core.

          • Marco Parigi says:

            “Otherwise higher internal pressure would likely disrupt the comet”; “the comet […] wouldn’t have survived for long enough in the inner solar system to allow for heat transport into the deep interior”; “the supervolatiles would have shielded the interior from warming”: all of these scream out at me as statements relying on values of quantities that cannot have been measured, only inferred or modelled or assumed without any justification.

            I can envision a core temperature of a few tens of degrees Kelvin as a thought experiment. I just can’t see it occurring naturally without violating several reasonable – if not evident – properties of the comet and its likely environment over the last few hundred years.

          • Gerald says:

            Hi Marco,
            it’s inferred from observations, measurements, and physics.
            Even the most direct measurements are inferences, at the end, derived from instrument counts/voltages and instrument calibration, from data received via radio waves and receiving antenna, software compression and decompression, etc.
            It’s too easy to discard anything contradicting one’s own presumption. Science works different.

            Noone has ever been in Earth’s mantle or core, that’s just inferred from measurements. But you accept it, because it’s consistent with Wegener.
            I accept it, because it’s inferred from measurements and generally accepted physics.

    • Marco Parigi says:

      One thing I might add is that the bar is set very high for any of the things such as stretch to be considered alongside modellable mechanisms. That also goes for liquid water as can be attested by Mars. However, circumstantial evidence is certainly a cue to look closer.

      My start at a succinct summary of the circumstantial evidences:

      • Gerald says:

        Hi Marco,
        nice. It fulfills at least the “concise” criterion.
        Now let’s see, whether you’ll find convincing evidence for something, the mainstream didn’t notice yet.
        With each attempt you’ll improve your skills.

        • Marco Parigi says:

          Hi Gerald,

          If I try to be any more persuasive with the evidence we already have amassed, it will stop sounding sincere. It is time for the comet to give the clinching ongoing stretch evidence, and the mission scientists obviously will have to stop assuming instrument or other error to explain the discrepancy in neck length 🙂

      • Marco Parigi says:

        Hi Gerald,

        As a follow on from my succinct Abstract, the following link

        shows a 3D mini match along a stretch which the large scale 2D (2D because it traverses the relatively flat expanse of Hathor) match completely constrains to be on a particular stretch.

        I challenge anyone to understand this match and not have an OMG moment..

    • Marco Parigi says:

      Hi Gerald, I thought I might copy this interesting thread here.
      Re: observations” , I said:
      As one option in your own advice. Is the comet morphing or eroding? We don’t even know yet, but the shape model is taking erosion into account (as evidenced by the smoothing of small features) but is not taking morphing into account (as evidenced by the correct CONSERT triangulation mapping to the wrong spot by about 50m on the “latest” shape model) ..
      Gerald says:
      26/10/2015 at 14:36
      Hi Marco,
      please don’t try to exploit obvious measurement errors as evidence. That’s a clear dead-end.
      One of your idols, Alfred Wegener, used distance measurements which were 1 km off as evidence for continental drift. Don’t repeat this error. It reduces credibility. Reviewers just discard this kind of pseudo-arguments as noise.”

      You may not have realised, but we, as many other interested observers are trying to work out what the go is with the measurement of Philae’s position. There has been no official determination of a measurement error, which for such sophisticated and accurate imaging is a BIG DEAL.

      How does an error far bigger than error bars creep in without a known cause? It is at the very least, an unwanted embarrassment for the modelling team, which they would be desperately trying to get to the bottom of.

      • Gerald says:

        Hi Marco,
        they knew about the risk of errors in the early CONSERT measurements.
        If I remember correctly, the shape model has been work in progress at that time. Unfortunately I don’t remember the exact source to base this properly.
        They needed to work with the best they had available, despite being preliminary. Would there have been other options?

      • Marco Parigi says:

        Hi Gerald
        The model is constructed in stages Ellipsoids are used for the two lobes, and calibrated images are used to place a texture on the lobes using automated software. The neck is then added.

        The centre of mass is used for the coordinate system to pinpoint both Rosetta and particular areas on the surface..

        The coordinate system is very sensitive to error (or morphing) of the neck measurement. If the neck measurement is out (or changing), every surface coordinate will be out by that error amount (or by the amount that the neck has changed relative to the model)

        Doing the model this way has its advantages, but the neck measurement ideally has to be accurate to the closest metre. The neck measurement has been neither publicised nor been scrutinised for what the error bar is. The team working on the neck measurement is either incompetent or confused by spurious data. It would be nice to know what is happening given the importance of this in the finding of Philae.

        • Gerald says:

          Hi Marco,
          permanently shadowed and hidden areas cannot be modeled properly in 3d.
          And 3d modelling isn’t easy.
          I’d suggest to try it yourself before complaining.

        • Marco Parigi says:

          Hi Gerald,
          A properly trained brain will beat computer based 3D modelling hands down. For instance, a scaled Navcam image measured with a ruler on a screen can be a check for the sorts of things a computer model can get way wrong. The computer gets it wrong because humans program it wrong. This is not the problem I have. The problem is that even the most rudimentary dimensions are not being communicated to the public. The dimensions we have, have not been updated in more than a year. Correct me if I am wrong.

  • Bill Harris says:

    Bravo, Dr. M. That summarises a good approach.


  • A. Cooper says:

    Dr Massironi

    Thank you for taking the time to engage with the Rosetta commenters and give your own comments on stretch theory. 

    This would be a good opportunity to reiterate that commenter Marco was the first to suggest stretch theory, for other comets, long before Rosetta arrived at 67P. He prompted me to start the stretch blog after seeing my Rosetta blog comments about the purported head-body matches.

    I shall comment more fully in due course but wanted to get this comment with my thanks to you and attribution to Marco as close to the top of the comments thread as possible. 

    • emily says:

      Dear A. Cooper and Marco,
      Apologies for mis-representing the originator of the stretch theory – I have updated the blog post to better reflect that.
      Best wishes

      • Marco says:

        Aww. shucks… 🙂

        • Marco Parigi says:

          Just changing my handle to my full name, Marco Parigi, as there are other Marco’s out there as well as on the Rosetta teams. Also, some of my family don’t believe it is really me…

  • Martin Klocke says:

    As a geologist I can only agree with Dr Matteo Massironi. Even if some words sound lecturing, it is a learning process for every young scientist. And a thorough revision of scientific manuscripts can be a hard experience…but no personal criticism. It is a fundamental part of the process.


  • Marco says:

    Hi Matteo,
    Thank you for your detailed reply and engagement with this fabulous blog.

    Alfred Wegener, and also historically Galileo are my scientific “heroes” and consequently, those scientists that sided against them at the time they initially produced their theories, are the opposite of my heroes. As much as you say Alfred Wegener had overwhelming evidence, his theories spent decades on the outer of geology regardless, and he died before they were accepted.

    My idea of “stretch” with regards to comets predates the arrival of Rosetta. The Hartley fly by photos in particular, with its smooth neck with a circular cross section and separate, independent lobes convinced me, even knowing that stretch had been “ruled out” by knowledgable scientists. This has been, not due to observations, but a lack of a stretch outcome from any theoretical models.

    This is the true reason stretch has not been considered from the start, and I guess I am disappointed that it hasn’t been mentioned outside the comment thread of this blog.

    I am not “in love” with stretch theory so much as have a suspicion that it is right and that my suspicion of why it is correct is also right. The background theory is so far removed from conventional cometary science that I could not reasonably address it here. At this stage, I find stretch theory to be “falsifiable” to a very large degree, in that I am hoping routine Rosetta observations can falsify it and my crazy theories can be laughed at and I could go back and think about some other scientific issues.

    My initial reaction to the finding that C-P also had two lobes was that it also stretched, but that there would be little to no evidence that could bear on it unless it was still stretching, and beginning and end measurements of the length of the comet may be the only way to prove even that remote possibility. It is still a possibility.

    When A. Cooper had independently suggested stretch due to matching features on the lobes, I encouraged him to demonstrate that evidence, because he actually did it in the opposite direction to me. I had a crazy theory in which stretch was something that all comets do, and A.Cooper had evidence that the two lobes were once connected, and the only way that could be was if it had stretched.

    We are likely to co-author any formal papers on this and your 4 points will be taken in mind. We are very familiar with the scientific literature with this. I have had an obsession with comets since 2012 and have read as many articles of interest that I could fit in.

    There are many lines of evidence for stretch, enough of which fit into your template that I am confident even you will see ones picked out in this regard.

    Dr. Massinori, I know that you too will realise that stretch happened, and I hope that you will be one of the early “converts” because we have challenged you thus. You will only see the merits if you try to prove it wrong (as I have, with A.Coopers evidence, and failed). Science is not about holding on to theories, even if you have just triumphantly declared the question had been answered in a peer reviewed paper.

    We will, through this blog’s comments, point you to specific evidence that you are likely to also see for yourself, probably in advance of any paper.

    Regards Marco

    • Harvey says:

      As soon as you say, ‘
      ” I know that you too will realise that stretch happened”
      and in another post “when it is proved correct” I’m afraid you demonstrate very clearly the problem of ‘being in love with your theory.’
      This is not a mind set compatible with objective science; its far closer to religious belief.

      • Marco says:

        Hi Harvey,

        I can see why you think that. Have I not given clear criteria that will prove me wrong? The big difference between religious belief and scientific hypothesis is falsifiability. I am not in “love” with any theory. My boldness is more the willingness to look stupid after the criteria is evaluated. Plus I don’t really mind if the mission scientists keep ignoring stretch theory on the basis that it fits the profile of a religion.

        • Harvey says:

          My comment does not relate to the effect such attitudes have *on others* (though it will be negative); it relates to the effect it has on the person’s approach to the argument.

          A ‘good scientist’ does *NOT* go into the lab, read a new reference, start doing a bit of maths, to ‘prove his theory right’.
          He/she does that to *TEST* the theory, – perhaps hoping for a given outcome, but absolutely open to the opposite result; nothing ‘negative’ can be overlooked, ignored.
          If you do not take that attitude, all too easily that Lab result that ‘doesn’t fit’ gets missed out; the paper with contradictory evidence is ‘overlooked’; the math that was ‘headed the wrong way’ doesn’t get completed. This is in many ways far more subtle and dangerous than deliberate fraud. It’s a form of self-deception, hard for the person concerned to recognize & face up to.

          If I heard one of my PhD students using phrases like that, I would be seriously concerned about their approach, & seriously concerned that – completely unwittingly – their results will be unreliable & potentially biased. We would be ‘having words’ 

          • Marco Parigi says:

            Hi Harvey,

            Point taken. My rebellious attitude to science is probably why I went into Engineering. It’s hard to argue with science that makes things work.
            I am trying to find evidence that will disprove stretch easily, but I certainly think the evidence of models is only as accurate as the assumptions of the models.

            I accept that the interpretation that there is a lack of stretch solution to billions of model runs disproves stretch as a possibility from the get go. I have known that since Gerald mentioned it. I do not believe that it disproves it at all, and I have had ideas about that, but certainly no proof about why there is no stretch solution to the models.

            That is something for the modellists to ponder, but it doesn’t take away the positive evidence, and model runs are *NOT* repeatable observations. The comet is doing the experiment for us, and we have to look there as to the evolution of the shape.

          • logan says:

            Is Matteo teacher also? Indeed we should learn science with boring things, like bags of random seeds, or small hardware. So we focus on method.

          • A. Cooper says:

            To Marco Parigi, the commenter formerly known as Marco 🙂

            ” The comet is doing the experiment for us, and we have to look there as to the evolution of the shape.”

            I have a feeling we may hear that quoted far and wide in the future

          • Harvey says:

            Marco; thanks for ‘taking the point’; it is a very serious issue in science, and it needs to be actively taught.
            You might be interested to know I’m half engineer, half physicist; I’m both CPhys and CEng etc etc for example.

            As I’ve often said, ‘stretch’ doesn’t seem ‘impossible’ in the sense that it grossly and obviously violates physical laws as the EU nonsense does. I’ve always found contact binary intuitively rather improbable, and rather favoured some sort of selective erosion process. Intuitively I certainly have just as much, if not more problems with ‘stretch’ as I do with contact binary. But he paper makes a decent case for contact binary; I’d stop short of saying anything like ‘proves it’ myself; ‘prove’ is a very strong word in my book.

          • logan says:

            “…and model runs are *NOT* repeatable observations.” This one really intrigues me, Marco Parigi. Was thinking of “repeated observations”.

          • Marco Parigi says:

            Hi Logan,

            Because we really do not have the opportunity to spin up real planetary bodies, modellers get this false illusion that a probablistic result of the models is the actual probability of the reality they are modelling. Thus zero stretch solutions makes it impossible as an example.

            We have the opportunity to see now some real morphology changes and deduce that which is changing it. This is real observations and we can repeat these observations and see processes repeat.

            Repeating a model run will repeat the same (some will be wrong) assumptions each time.

      • Marco Parigi says:

        Hi Harvey,

        Back in July you said:
        21/07/2015 at 18:49
        A further thought re liquids.
        Actually it should be quite easy to give a strong boost to a ‘liquids’ theory if someone can be bothered to do the analysis – or indeed to deny it.
        On earth, large diameter high-g environment, we are used to liquids forming ‘flat’ surfaces with a surface normal to the gravitational field; a tangent plane to the sphere.
        But on 67P gravity often does *not* ‘point straight down’ into the surface but is all sorts of odd directions,
        So if the flat areas are liquid generated they should be orientated normal to the local gravitational field & *not* locally tangential to the comet surface, where those two differ as they certainly do in some areas.
        Locate such areas & if they contain a flat feature check, & fluids will be quite strongly supported – or pretty much rules out.

        End quote.

        I realise on looking back that Dr Massironi has done this for us! Maybe we can say that the plains being normal to the local gravity vector as described for most of the strata is a vague evidence that liquids have something to do with the formation of the strata. A great majority of flat areas are within 2% to 4% to being normal to the gravity vector….

        • Harvey says:

          Capta problems again.
          A very good point.
          Of course the authors put a different interpretation on it, that it originates from the early accretion process.
          Given the temperatures and materials available I’m inclined to the tentative view that any ‘liquid like’ behaviour is more likely to be a fluidised dust bed than a true liquid. That can easily exist under comet conditions, unlike true liquids which are difficult (not quite impossible.) it also removes all the complications caused by surface tension, Marangoni flow etc.
          True liquids would behave in very bizarre ways on 67P!

        • Gerald says:

          Hi Maro,
          the horizontal layers are by Steno’s law. No evidence for liquids. I’m almost tempted to the contrary, since liquids can overcome this rule, if energetic.
          We also don’t see evoporites or altered rock. So, if there are liquids, they are confined to small locations, such that the effects aren’t obvious.

          • Marco Parigi says:

            Steno’s Principle of Superposition
            “At the time when any given stratum was being formed, all the matter resting upon it was fluid, and, therefore, at the time when the lower stratum was being formed, none of the upper strata existed.

            I don’t know Gerald. Matter resting upon it was fluid. Sounds like Steno would insist that would normally mean liquid. It sounds like special pleading because “comets are different”, yet Steno’s law is grounded in Earth like processes. I don’t see why the lack of gravity precludes the need for fluid in the process, nor why Steno’s law would necessarily apply in space microgravity.

          • Gerald says:

            Hi Marco,
            the assumption of a fluid is probably a little too narrow.
            You get this layering for settling of dry dust or sand, as well.
            But for a first understanding of the principles, thinking at sedimentation within a fluid is ok, if it helps.
            Of course one needs to stay cautious with comets, since not every principle can necessarily be transferred from Earth to comets without any modification.

          • Marco Parigi says:

            Hi Gerald,

            The assumption of a fluid is neither too narrow nor too broad. Even in the example of hailstone growth rings, where gravity is not a factor, liquid water condenses on the outside and the layers freeze from the already frozen hailstone, while the liquid surface tension etc holds the shape stable enough to form a layer, whereas a lack of liquid would not.

            No gravity required for hailstones except for falling through the clouds and to the ground. Hailstone growth does not rely on gravity, but does rely on fluid!

            If it was too narrow, it wouldn’t have been included in a LAW. Reinterpret aspects of law at your own peril. What can we bend with the second law of thermodynamics? Or Coulomb’s law?

          • Gerald says:

            Hi Marco,
            you may know of the law of conservation of energy (first law of thermodynamics).
            It’s actually much more complicated, when considering gravity; you need to consider the stress-energy tensor, instead:

            Each of these laws of physics has its assumptions.
            When weakening these assumptions, one needs to review the conclusions and validity of the law.

            The second law of thermodynamis: I remember, that Roger Penrose tried to understand it:
            Stephan Hawking had a try:
            But I’m not sure, whether it’s fully understood by anyone in the meanwhile. Beyond my limited skills. Needs a full understanding of the arrow of time to find its limitations.

            Regarding Steno’s principle of superposition in the traditional form: It assumes the presence of a liquid, with sediments in suspension.
            Weakening this assumptions to a dry environment, one needs to review the consequences for grains forming a sediment. As a result of this review, one finds out, that these principles essentially hold for non-liquid environments, e.g. sediments by fallout of volcanic ashes.
            In this case air takes the role of the fluid.

            We may then think about accreting dust (and ice) around a cometesimal in the absence of air.
            The principle of superposition still holds, since the accreting dust cannot penetrate deep beneath sediments; and it forms sediments itself, after contact with the surface.

          • Marco Parigi says:

            Hi Gerald,

            You have a point with weakening the assumption of suspension in fluid needing to be tested in dry environments, however, with the following –

            “As a result of this review, one finds out, that these principles essentially hold for non-liquid environments, e.g. sediments by fallout of volcanic ashes.
            In this case air takes the role of the fluid.”

            The example (and other examples besides) generate sub assumptions that then also need to be tested against the space environment.

            For sediments by fallout of volcanic ashes, the fluid model only works in the assumptions of atmospheric air pressure AND planetary gravity being required to “herd” the particles in a way which is analogous to liquid suspensions. Take away these assumptions and you are back to square one. There is no empirical example of dry ice and dust in microgravity doing anything like Steno’s law. Again you need to go to untestable, theoretical (implausible) scenarios immune to falsifiability criteria to apply Steno’s principles.

          • Gerald says:

            Hi Marco,
            the field of gravity around 67P is still well-defined. Free fall is just slower than e.g. on Earth.
            If it would be microgravity, it could be testet e.g. on ISS.
            For other low-gravity tests you may use freefall towers. But since these experiments are limited to a few seconds, they can only be performed in small steps. Not untestable in experiments, but difficult.
            Based on these short experiments, you may run computer tests – I know Wegener couldn’t do it, so you dislike them. But these accretion tests are rather simple to implement as a software. When running the software you can observe the growth of the accreting body, or the paths of the particles.
            On Earth you may run experiments under “normal” gravity in vacuum, to test for the influence of the atmosphere.

            Related is e.g. thin film deposition:
            It shows, that layers grow in (near) vacuum, as well.

          • Marco Parigi says:

            Hi Gerald,

            I don’t have the opportunity to test the computer model in a real accretion disk with real ice and dust to demonstrate that it wouldn’t work to form layers that would then be resilient for 4 billion years. This is the point I am making. Your hypothesis that Steno’s principle works in this situation is not falsifiable, yet not evident either.

          • Gerald says:

            Hi Marco,
            I’ve given examples related to the formation of the comet supporting the applicability of Steno’s principles to 67P. More examples could be added.

            Where are the counter-examples justifying doubt?

          • Marco Parigi says:

            Hi Gerald,

            The counter examples I cite are in the space station. Things like sugar, cinnamon, crushed ice, etc. are essentially banned in favour of things like pastes and liquids. This is because there is no way to herd them effectively, and C-P gravity wouldn’t help. All the examples you cite are extremely contrived, and the assertion they would just happen in an accretion disk with little gravity is not realistic.

          • Gerald says:

            Hi Marco,
            that’s excuses, no counter examples.
            The issue with ISS can be overcome in a reduced gravity aircraft:
            Your experiment can last up to 25 seconds.

            Or less expensive, an example of drop tower experiments:

        • logan says:

          Hi Marco Parigi: Some months speculating that preceding ‘accretion’ entities are ‘grow’ entities [no particular reason for roundness].

    • logan says:

      “…and my crazy theories can be laughed at…”

      Consider the most valuable people those around here defending ideas out of mainstream. Speaks of skepticism, independence and bravura.

      As for myself, probably no Soul here have said more crazy ideas. Never have intended of them to be more than wander and wonder. No soul have laughed at me. Neither expect from any of you -and less from Teams- to agree with me. Just contributing to the Imagination Pool.

      No soul is laughing at you.

      On the other side, this is not a “side” issue. No soul care about siding with, or against you. Not even me. Stretch arguments -yes, arguments- have a life of their own. And even if yourself become unconvinced of it on your old age, that idea will survive you.

      You are not your ideas.

      • Marco Parigi says:

        Hi Logan,

        Re: “you are not your ideas”

        If you knew the ideas I was talking about you should not be so sure. I’ve invented words to describe them (Marconomics, Marcomony) that put my way of thinking as formalised philosophies. They are me and apparently, no one else.

    • Gerald says:

      Hi Marco,
      once again, spin changes of asteroids and KBOs, and the resulting effects, have of course been considered (since decades) :,514.pdf

      Btw., here a link to Alfred Wegener’s 4th edition of “Die Entstehung der Kontinente und Ozeane”:
      He explained several largely independent lines of evidence, some of which turned out to have been heavily flawed (best example the wrong early distance measurements between continents, and conclusions).
      The conclusions were essentially correct, but based on spurious evidence, an example for “wrong assumptions can result in.correct results”.
      But due to the independence of the arguments, most have turned out to be correct, and have been confirmed and refined by himself and by other investigators.

      “Stretch”, however, is based mostly on just one geologically and statistically questionable method.
      It isn’t backed up by a valid theoretical model.
      Hence the basis for “stretch” is very fragile.

      Reagarding the roles: Wegener’s continental drift is now established. How do you know, that this established model isn’t just the wrong one for the comet?
      As wrong as established fixism around 1900 A.D. has been wrong for oceans and continents on Earth?

      • Marco says:

        Hi Gerald,

        Fragile is good for any hypothesis because that relates to its boldness and falsifiability (see Popper).

        There are several independent lines of evidence with stretch theory see the blog regarding slab loss, monolith displacement, neck crack locations, 3D mini matches within large scale matches, and rotational alignment with certain features.

        I guess you could label them as “circumstantial” individually compared to statistical matches, but I fail to see them as “mainly one” line of evidence or one method.

        My pre-Rosetta arrival hypothesis was and still is, separately to A.Cooper, that the established model for comets is equally incorrect for all comets. As far as that goes, I guess you could say that I am running with a hunch and using it to predict unexpected data from Rosetta rather than detailing the basis of my hunch as the basis may not be justifiable even if it is correctly predicting new facts. I could just be getting lucky if I hit an occasional jackpot. Or I could be very wrong.

        So the fact that my hunch is predicting is current neck stretch in the order of 5% per perihelion which would be around 50m stretch between October 2014 and March 2016, which I assume will be the most accurate before and after measurements.

        I realise that models consider this to be virtually impossible.

        • Gerald says:

          Hi Marco,
          re lines of evidence: “Stretch” is based mostly on subjective interpretations of surface topography.
          Other lines of evidence, like chemistry, stratigraphy, model simulations, formal verification of the subjective interpretations, actual data of ongoing 3d-distortions are missing.

          The pre-existing models are simplified, e.g. rubble pile models work mostly with solid spheres. That’s of course inaccurate. They may need to be replaced by fractal heterogenious grains, at least to account for the high friction angle.

          A “hunch”, or a good intuition, is o.k., initially.
          Remember Edisons remark: “Genius is one per cent inspiration, ninety-nine per cent perspiration.”
          You may know of the countless attempts of Swan and Edison to find a material for the filament:

          Einstein needed many attempts to find the field equation of general relativity.

          Probably the king of generating false proofs is Fermat’s last theorem. More than three centuries of uncounted spurious claims of a proof, still ongoing, depite Wile’s eventual success.

          The first attempt rarely turns out to be correct.

          • Marco Parigi says:

            Hi Gerald,

            I’m sure the OSiris team has the actual data for ongoing distortions. When they bother to share that data it would be right to criticise our lack of data if we fail to use it. For now, the theory is awaiting the data to falsify my claim that the neck is longer than before.

          • Marco Parigi says:

            Hi Gerald,

            In this case it is 1 percent inspiration, 99% waiting for Rosetta data that *will* either falsify stretch or allow it as a possibility as a plausible hypothesis.

            The perspiration can come after that. Stretch theory explains what is observed, or will be. It can not explain the models failing to allow for stretch. This other than real life comet nuclei are really complex, and the models “assume spherical horses” as it were for the elements in simulation, and it is unclear whether more sophisticated models would help or not..

      • Marco says:

        Hi Gerald,

        With Wegener, you are not addressing the issue that I have with the “peer reviewers” of the time rejecting his theories despite, as you say, independent lines of evidence. The science of Geology was set back for decades on a technicality that continental drift had no provable mechanism to go with the independent lines of evidence. I think the setback to science is s a tragedy dressed up as the conservatism of science doing its job. History is revisionist in that few people realised that Wegener did not get any credit for the theory until after he died, which I believe to be quite unfair given the solid evidence. I think his scientific peers failed the betterment of science.

        • Gerald says:

          Hi Marco,
          A. Wegener got his ideas and research published, and he triggered a lot of research during his lifetime.
          The majority of researchers has been wrong at that time. That’s almost always with new ideas, although the idea hasn’t been quite new at that time.
          But doesn’t mean at all, that new ideas need to be always correct; most of it is garbage.

          • Marco Parigi says:

            Hi Gerald,

            I see a lot of good ideas outside the system get ignored. Not even necessarily about the one at hand, but the system equally throws out the good with the bad.

            I guess overall the peer review system allows reviewers to “protect their turf” while giving all the appearance of just stopping the garbage.

          • Gerald says:

            Hi Marco,

            false negatives as well as false positives occur.
            The system isn’t perfect. Maybe good so.

          • Marco Parigi says:

            Hi Gerald,

            The system is revisionist in nature. At any one time the peer process makes a call on whether something is “false” (positive or negative) If it is the system itself that makes the wrong call, the system is not capable of revising itself or detecting that there is a problem. Problems and solutions to the system must necessarily come from outside the system. The system failed Wegeners ideas, and no argument from within the system is going to fix the problems I’ve flagged.

          • Gerald says:

            Hi Marco,
            Wegener faced the problem of insufficient evidence to be clearly better than the several competing hypotheses with their own evidence.
            It took until the early 1960s, when the discovery and investigation of the Middle Atlantic Ridge provided the overwhelming evidence for plate tectonics.
            “The system” needs this kind of clear indication to throw the old ideas overboard.
            Without this laziness we would naively believe anything without appropriate verification. The result would be rather erratic zigzagging. The ancient greeks suffered a little under “this every idea is good” philosophy.
            You need a filter in order not to end up in chaos.

          • logan says:

            “…”The system” needs this kind of clear indication to throw the old ideas overboard.”

            Even if the new clues came from outside the “System”, It was the “System” who determined the clues valid an relevant to Alfred Wegener theory.

            And no, the “System” doesn’t “throw overboard” the old models, just delimit universe of application. Sometimes the universe of application becomes empty.

          • Marco Parigi says:

            Wegener faced the problem of being a German scientist at a time of being on the wrong side of coming World Wars.

            These alternative hypotheses you talk about were actually collections of virtually unfalsifiable assertions.

            The truth is, Wegener’s ideas suffered under politics masquerading as the conservatism of science. Poppers principles were basically fed to the wolves (although he was a German 20th century philosopher so I guess his ideas were more in vogue after the world wars also)

          • Marco Parigi says:

            Hi Logan,

            Regarding your quote:

            “Even if the new clues came from outside the “System”, It was the “System” who determined the clues valid an relevant to Alfred Wegener theory.”

            That really is not what the evidence shows. The evidence shows, that in the US especially, geologists only reluctantly accepted the theory, when overwhelming mid ocean floor evidence came to bear on it, while still declaring Wegener’s “clues” invalid to base a theory on.

            The “truth” is, continental drift was happening regardless whether any of the experts believed it was happening.

            No one is going to go back and find that in fact the Earth is the centre of the universe, that the seas sunk to where they are today. The “truth” of heliocentric model and continental drift was hiding behind layers of parsimony.

          • Gerald says:

            Hi Marco,
            politics was a problem between 1933 and 1945. Wegener died in 1930.
            Otto Hahn, Albert Einstein, Karl Schwarzschild (died 1916 in World War I), Werner Heisenberg, Max Planck, and many others got their results established at the same time Alfred Wegener tried to establish continental drift, although their work was at least as revolutionizing as Wegener’s.

    • A/Prof Simone Harrison says:

      Congratulations to Marco and colleagues for presenting their viewpoint. Science only progresses because of the curiosity of many and the courage of a few to challenge current theories. Keep challenging us all and focus on collating all the evidence you can, both for and against and don’t be put off by criticism. Scientific debate can be a valuable tool in the quest for knowledge.

      • Marco Parigi says:

        Thanks Simone,

        And hopefully you haven’t heard the last of stretch theory….

  • Ana says:

    Dr. Matteo, thank you. You really are a scientist. I had the honor to meet other scientists in my life and they show a similar, logical and ordered way of thinking. People commenting on this blog are not scientists. It is a honor for us to have an answer from someone like you.

    However, there is something that gets me confused. I quote from the previous blog post:

    “Layering has also been observed on the surface of other comets during previous flyby missions, suggesting that they also underwent a similar formation history.”

    Please, can anyone give me a link to an article or a picture showing stratification exists on other comets?

    Thank you.

    • Kamal says:

      Ana: Quoting from the article, hope this helps:

      Terraces and localized strata are not new features of cometary nuclei, having been observed at the surface of comet 9P/Tempel 1 (refs 8 and 9) and, possibly, of comets 81P/Wild 2 (ref. 10) and 19P/Borrelly (ref. 11). …
      However, the OSIRIS images of comet 67P/Churyumov–Gerasimenko provide evidence of global stratification with an imaging resolution of up to 0.1 m per pixel, greatly exceeding that of previous close-range images, the best of which are around 7 m per pixel (refs. 12, 13)

      And the references are:

      8) Thomas, P. C. et al. The shape, topography, and geology of Tempel 1 from Deep Impact observations. Icarus 187, 4–15 (2007)

      9) Thomas, P. C. et al. The nucleus of Comet 9P/Tempel 1: shape and geology from two flybys. Icarus 222, 453–466 (2013)

      10) Brownlee, D. E. et al. Surface of young Jupiter family comet 81P/Wild 2: view from the Stardust spacecraft. Science 304, 1764–1769 (2004)

      11) Britt, D. T. et al. The morphology and surface processes of comet 19/P Borrelly. Icarus 167, 45–53 (2004)

      12) A’Hearn, M. F. et al. Deep Impact: excavating comet Tempel 1. Science 310, 258–264 (2005)

      13) A’Hearn, M. F. et al. EPOXI at comet Hartley 2. Science 332, 1396–1400 (2011)

    • Gerald says:

      “People commenting on this blog are not scientists.”
      Some are, some aren’t.

  • Bill Harris says:

    Comet Tempel-1 (the Deep Impact mission comet) shows nice stratification or “regional differences” and Comet Borrelly shows inferred layering.

    I’m an advocate of the “contact binary” observation, but I’ve always had trouble drawing that fuzzy gray line between an actual contact binary and a c comet accreting from chunks, pieces, boulders, dino-eggs, bigger boulders and really big big boulders and so on. In a sense, a cometary body is still accreting with kilometer-sized fragments.


    • logan says:

      Hi Bill. Agreeing as an outsider. Maybe if we have a comet-esimal duo gravitationally ‘drifting’ outside of formative environment, could name it “binary” as a more or less “permanent” status. Just wandering.

  • Thomas T. says:

    Interesting discussion. Maybe it is possible to sum this up into a scetch explaining the observations and model.

    If this is the result of a collision, can this be simulated in a lab? It would be really interesting to observe such collision to understand circumstances that led to the current finding of 67P.

    Another question: is it possible to observe changes in the rotation of the comet in the last year?

    • Gerald says:

      “…is it possible to observe changes in the rotation of the comet in the last year?”
      Yes, a change (or better changes) of several minutes for the rotational period has been observed.
      The data are provided in SPICE kernel files. But some of these files are in a binary format, needing appropriate software to be readable (for humans).

  • Guili says:

    Was thrilled to read a reply from the author, then read this:
    “As a scientist, I do not normally read works that have not been rigorously reviewed and published in scientific journals.”
    Give me a break…

    • logan says:

      As time being a limited resource on work issues, you focus on ‘leveraging’. This is relevant to any profession restricted by optimization polices. [Maybe the comment could be taken on a ‘social’ context].

      • Guili says:

        As you may have guessed, I understand the constraints but I don’t understand the conclusion.
        It see it as the equivalent of consanguinity on DNAs.
        And since it is done on purpose, I find it arrogant. As if a never-published-idea/person was automatically irrelevant

        When studying the unknown, you should keep a very open mind instead of trying to base all you work on previous recipes.

        And I won’t even start talking about the astounding number of wrong/falsified scientific papers which is another reason for not keeping them as your sole source of inspiration.

        • Gerald says:

          I think, it’s mainly a matter of available time.
          Reading papers, conferences, own work. Ressources are limited.

  • logan says:

    Hi Ana. “People commenting on this blog are not scientists”.

    Most of us are just citizens enjoying and learning from the experience, but indeed have the fortune of having scientists writing here, our Editors -who contribute the initial posts and even manage as Moderators- have the highest credentials, and even Team members -like recently Dr. Massironi and Dr. Altwegg (We even had Matt in a “what’s up” mode recently -should I say “what’s down” mode?-) [apologies if missed a recent one]- are dropping by at times 🙂

  • Mark Peifer says:

    I suspect Dr. Massironi was reviewer #3 on my last manuscript. Seriously, though, the points he raises about the scientific process are excellent ones, and also point out how the review process can improve our work. Even before formal review, as scientists we learn to argue from the data, to challenge one another, and to constantly be willing to revise our thoughts as new data comes in.

    The one point I might challenge is the statement that “As a scientist, I do not normally read works that have not been rigorously reviewed and published in scientific journals.” While I do agree the review process is valuable in vetting work, I certainly am constantly exposed in my own field (cell biology) to lots of unpublished, un-reviewed and often very preliminary data, from colleagues near and far. I use my own critical skills to assess the quality of he data and the conclusions drawn, as I am confident Dr. Massironi does as well.

    • Marco Parigi says:

      Hi Mark,

      I am actually disillusioned by the peer review process. I think what Dr. Massironi is trying to say is to not believe in anything that has not been peer reviewed. As a scientist, getting ideas from people, even other scientists is qualified by how many peer-reviewed articles they have, or have been cited.

      From the outside, it gives me the impression that it encourages conforming to the peer, and there is significant pressure not to contradict any articles that have passed peer review in the same branch of science.

      This has the tendency to kill off any truly new ideas whether they have merit or not.

      I suggest that whether it is peer reviewed or not, judge an idea on its scientific merits. Massironi has glossed over the question marks on contact binary, and has not addressed the matches per se, but implied they are not based the Osiris model and thus cannot be relied on, especially from those without qualifications on geological grounds.

      I think peer reviewed articles should still be read with a skeptical scientific eye, and ideas from outside the peer should as well.

      • logan says:

        Hi Marco Parigi. Matteo is only asking for a few more neurons to have palated it, and not returned it.

        Why are you reclaiming time allocation from main investigators? Is this -an open to the general public blog- a place to solicit time allocation from Scientists on active missions?

      • logan says:

        Nothing farther than ‘conforming’ on science. Just get some souls with credentials on the scientific method. Any discipline, as for not being complacent.

      • Harvey says:

        Your views on peer reviewing are fairly widely held, and in some degree justified.
        But they apply primarily to *poor* peer reviewing, and *poor* editing.
        As editor of a scientific Journal, I would not dream of taking any notice of a review that said, as a paraphrase, ‘this contradicts the accepted view so it’s wrong’; that’s a useless, poor review and would go in the bin.

        *Good* reviewing and editorial practise does improve the quality of the scientific literature, and does not suppress originality.

        This very negative viewpoint also overlooks some strong corrective features. In any field, there are quite a few places to publish. You will get your view seen if it’s technically correct, and in the end, it will get accepted if it’s right. Steadily more people see that, it gets cited, used, tested in new ways – and becomes the accepted view which might need to be overturned in turn!

        Good people with good ideas do succeed in ‘getting them out there’ in the end, and there is a strong impetus to do so. That’s the paper which will attract a huge number of citations, blow your H index through the roof etc, not another twenty boring ones.

        So yes it can be an issue, sometimes is, but in long experience, rarely if ever have I seen it kill something off that was in fact good.

      • Marco Parigi says:

        Hi Harvey,

        Not much more to add except that from the outside, my disillusionment of the peer review process runs very deep. Even in those cases where poor review is not a factor, there are structural issues related to parsimony which stops circumstantial evidence to even be considered evidence at all. Liquids on comets is a classic case in point.

  • Sovereign Slave says:

    Question: Regarding the specific surface features on P67 that lead you to your contact binary conclusions, have you ever encountered similar geological surface features here on earth, or is this the first time that you have ever found these features to exist anywhere?

    • Gerald says:

      Sorry for taking this question. Strata are almost ubiquitous for sediments on Earth and on Mars.

      Here a recent (of october 11, 2015) image of lamellae on Mars:
      Here a stitched image from Mars (Shaler outcrop, MSL, sol 120) :

      Similar layering occurs outside geology, as well.
      Here a nice image of hailstone growth rings:

      Hence stratigraphy and related fields apply rather generally.

    • Sovereign Slave says:

      Haven’t been able to read the paper, which obviously presents much more detailed information. But, to expand on my question above, was wondering about a few other things. Are there other geological processes that could also account for the P67 features that led you to your contact binary conclusions, or have you ever encountered similar features? I can’t be certain of course, but I would assume that if you’d discovered a totally new geological feature, this would be huge news unto itself and very much highlighted as a major event. So if this isn’t a totally unique feature, and it can be found in other places other than a contact binary, is it impossible for the features on P67 to have formed under similar circumstances to those? And if they could not because it is assumed that P67 formed (and then reformed) in the early solar system based on the primordial proto-planetary disk theory, if the proto-planetary disk theory were to be shown to be invalid at some point in the future, would this also invalidate your contact binary theory (if so, I have to wonder how many other theories would fall as well)? Also, do you still consider P67 being a contact binary to actually be a theory, or is it now considered to be fact. Based on statements made by scientists, such as, “Now, thanks to this detailed study, we can say with certainty that it (P67) is a ‘contact binary’,” it appears to be a completely settled issue (fact). Finally, regarding simulations, I tried to post this elsewhere (I think Captcha ate it though) in response to Gerald posting that the contact binary simulation is physically reasonable and possible. My response to him was that in court law, there is an important distinction between a simulation being used to present evidence vs a simulation being presented AS evidence. It is acknowledged that presenting a simulation AS evidence is a very dicey proposition filled with all kinds of potential errors, deceptive variables, and unreliability, and is treated accordingly. In a word, simulating that something might happen should not be used as evidence that it did happen.

    • Kamal says:

      SS: If courts and judges decided scientific theories then we might by now have moved a little beyond Galileo, who I understand got a pardon around 1992.

      • Ramcomet says:

        Good one Kamal, lol!

        However, Bravo to SS. His points hit the nail squarely on the head in regards to this paper’s overboard ‘factual’ implications, with its “unanbiguous” and “with certainty” claims and title.

        For me, this is not about defending Stretch hypothesis any longer. Now it is about giving this paper a proper “non-peer review” by the public free thinkers and scientists participating here.

        Again, as many others have said, I am continuously grateful to Emily and ESA for the chance and appreciate this blog immensely!

  • A. Cooper says:

    Dr Massironi

    Thanks again for sharing your thoughts. I’ll address your four principles in sequence. 

    Principle (1) “Be a good field geologist”. I’m not a field geologist so I’ve relied on expert opinion for 67P, as illustrated by the following.

    In December 2014 at AGU14, S. Marchi gave his preliminary findings on the stratification of 67P. We had only the media reports to go by:

    Quote from the article:

    “Using new images taken with Rosetta’s OSIRIS camera, Marchi and his colleagues found terrace-like layers on the comet’s body. The layering aligns perfectly with parallel lines seen on the opposite side of the body, suggesting that these layers extend through the body as part of its internal structure. Although the head also has layers, they don’t align with those in the body, which implies that the two lobes were once two separate pieces.”

    There was no mention of onion layers. The only interpretation one could make is that both head and body consist of flat, parallel strata. 

    I note you are an OSIRIS colleague of Marchi’s and that you were co-authors on the 67P impacts abstract for AGU14. I presume you agreed with the stratification scenario at the time as I can’t find any contemporary reference to onion layers. It seems onion layers weren’t being discussed by anyone. 

    That is, by anyone excepting Marco and myself. On January 3rd, Marco commented on Part 6 of the stretch blog with the Wired link above. He thought the “layers” were more concentric than parallel. I replied:

    “As far as the onion versus straight layers is concerned…In the final analysis, I think I do trust their actual observations and so I believe their assertion that the strata in the body are straight”.

    Those three dots pass over my own observations of concentric layers, which I repudiated in favour of deferring to expert opinion. 

    In one sentence I killed the discussion on onion layers stone dead and delayed the proof of their existence by four months. 

    In April, the first illuminated south pole photo was released. It’s in Part 11 of the stretch blog. The south pole head strata could be reconciled with the north pole “strata” only by invoking onion layers. So I suspended my deferring stance from that point. 

    My terminology switches in that post, from “strata” to “tiled”, “tiers” and “feathered”. I couldn’t assert they were onion layers. I’d only just made the observation and as you say, the order is observation, hypothesis, model, theory. So I mentioned in that post that there was evidence for head lobe stretch before shearing. That’s the hypothesis. The model was the sub-series, Parts 22-29 with features betraying the mechanism and finishing with the theory. The theory is that the onion layers deformed and slid over each other. That’s all four of your stages laid out in the correct order.

    Marco’s onion layers were both the impetus and the raison d’être for the sub-series. The onion layers have been described but not in detail. That’s because the sub-series is unfinished. It would have been finished months ago if we’d not deferred to the experts in January.

    Principle (2) “Be rigorous”. I’m as rigorous as I can be, given that I have only the NAVCAM images and no shape model. I’m quite adept at on-screen measurements. With each match, there are two mirrored areas that look very similar. Then it’s checked that one isn’t twice the size of the other (actually to within 2-4%), and that one sits directly below the other, both kiss their neighbouring matches and both fit in the third dimension.

    This accuracy is enough to warrant further investigation and is repeated with match after match, sequentially along kilometres of shear line. Further investigation is all I and Marco have suggested, especially the idea of OSIRIS cutting out the neck to see if the head rim does fit the shear line. I can even say where the slight discrepancies will be and why. 

    Principle (3) “Never fall in love with theories”. 

    You follow this statement with “the two favoured scenarios for Comet 67P/C-G’s formation because they do not present any problems to existing theories”. That sits ill with the stated principle.

    Your two theories are contact binary and neck erosion and yet CB does raise problems with existing theories. Your issues to be synthesised, as you say, are acknowledged as the problems. (ii) is the unresolved “collisional problem”, which might now shunt comet formation to the farthest reaches of the Kuiper belt. (iii) is the fairytale kiss of two bodies at 1.5 m/sec while orbiting at 0.4 to 4 km/sec with different orbital elements. The only way this can be achieved is with identical ellipses but with their perihelion points swung to induce a 0.14° crossover angle at hundreds of AU (or repeat using the inclination angle instead). 

    “Stitching of contact binaries through low-velocity collisions” per your linked paper, needs to be put back on the list as number (iv). That’s because the model run that did stick had a combined velocity of 0.375m/sec (1.5x escape v of 0.25m/sec). Here’s the supplementary page:

    This implies a 0.279m/sec cosmic radiant velocity, the one that matters. That’s 0.118 times larger than the escape velocity and a minuscule 3cm/sec above what is already absolutely known to allow them to stick or at least orbit. 0.375m/sec is “baby crawling speed” as commenter logan puts it- nowhere near “bicycle speeds”. 

    For 67P it translates to 1.5m/sec, and a 1.118m/sec cosmic radiant velocity. Right back to square one regarding razor-thin orbit crossover angles. 

    To be clear, I’m not questioning the “stitching” paper, just its being used to support CB theory for 67P.

    You mention under principle 3 that “…the comet derives from a contact binary of two comets with an onion-like interior.” However the onion layers at Hathor are sliced through and nowhere near perpendicular to the head lobe gravity vector. At Serqet, the outermost layer is bell-shaped around the rim. These two factors are consistent with stretch (bell shape) and then shear (Hathor slice). 

    Principle (4) “Be short” (and concise). 

    I’m describing detail which is at a resolution of 15 metres upwards while leading the reader along a narrow shear line through a landscape of considerable complexity. They can stumble 50 metres and be lost. It is necessarily complex and requires lengthy explanation. With patience, some do see the matches and once you see them you can’t ‘unsee’ them. They are unequivocally there.

    Being concise comes at a price. You lose the detail that comes from delving deeper and seeing in higher resolution. On arriving at the shear line, you have to explain that detail, including the pitfalls because the comet just happens to be a very roughed-up place. CB and erosion theory result from standing right back and ignoring the small-scale detail. But if you’ve already seen the detail, what do you do? Pretend you never saw it?

    You state under principle 4:

    “It seems that most of Mr Cooper’s observations are based on surface morphology with many primary and secondary features not correctly recognized.”

    This is due to deferring to Rosetta scientists’ expert opinion against Marco’s and my judgement. This hasn’t been the case since 26th April 2015 when I reverted to our original judgement on onion layers. 

    “He begins explaining the stretching hypothesis, providing the observations that should support his theory only afterwards”.

    From the first paragraph of Part 1, I present observations and lead on from there. You may have read the About page, which states the blog has “the sole purpose of proving [67P] stretched”. That means it’s a single-topic blog, not that there are no observations to back it up. And Marco’s urging me to start the blog was based on my observations alone.

    “his observations in support of the stretching hypothesis are only based on putative matching points recognised on the surface morphology.”

    That is a value judgement. For the matches to fit, they once had to reside inside the structure of the comet. They’re on today’s surface but that’s because they’re imprinted on the sheared-off onion layers. When joined, they were buried. Some matches go halfway down Hathor which one Rosetta scientist referred to as the comet “interior”.

    You mention the collimating of primary structures across faults but don’t address the essence of my matches which is that they are mirrored matches imprinted on what was the opening crevice on shearing. That’s the equivalent of crawling into the crevice and looking at which bumps and dips would fit back together on closing it up again. This is the only way of generating a match because, as you say, the surface morphology is changing. On shearing, the matches were set on both faces of the opening crevice, not in the surface morphology either side of the crevice. I agree it won’t retain matching features in the surface dust.

    In conclusion, I don’t need to write a paper. Stretch theory doesn’t need to be proven in peer review before it’s entertained as one of three competing scenarios instead of the two you mention. That would mean jumping to your stage 4 in order to go back and compete with the other two at stage 2 or 3. That’s neither fair nor logical.



    • Dave says:

      Re A cooper – reply to Dr Massironi

      Enjoyed your reply, I have followed yours & Marco’s blogs from the start, initially finding the concept incredulous, especially the matches but as time has gone on and the addition of more detail, I am now less incredulous.

      You have put in a huge amount of work which is impressive in its detail, As for religion, it seems to be that the main stream can be as guilty and indeed can be more zealous than some of the alternative theorists.

      I m not exactly a convert yet but good luck with it, I am eager to see the next instalments.


      • logan says:


        Obviously we have multi-players. Obviously this multi-players are pulling argumentation out of Scientific limits.

        Not going to work 🙂

      • A. Cooper says:


        A case in point: on the original “How the comet got its shape” thread, I was badgered for calculations as to spin-up required for the head lobe to stretch from the body. So when I provided them, including all workings and inputs so that anyone could reproduce them, I was told by my inquisitor that my comment was too long.

        You’re right, it seems that stretch theory is, well, just too much of a fag for anyone to sit down and really get to grips with. Unfortunately, the comet has a highly complex morphology. So, rather than really looking hard at how the features are interrelated and divining the mechanisms that brought them about,  it’s so much easier just to say everything we see is due to sublimation and erosion. 

        Understanding this comet requires getting familiar with every last detail, constantly relating very small areas to their surroundings and doing the same with large areas and at every scale in between the two. 

        It seems Marco and I are the only ones analysing it in this manner. The only reason I think that must be the case is that if anyone else was doing so, they’d see that it’s stretched. 

        By the way, thanks for “sitting down and getting to grips with it” yourself! It seems you’re a rare breed…

      • logan says:

        “…impressive in its detail” Detailing up to saturation is not impressive at all. You are not asking for a sensitive answer if you saturate attention and senses of your interlocutor.

        Saturation is an aggressive behavior, certainly here and all around this galaxy.

        • logan says:

          Lions roar in order to saturate ‘directionality’ on the auditive sense of pray.

        • Marco Parigi says:

          Hi Logan,

          The detail is necessary if anyone wants to understand the matching 3D shapes and all the other amazing detail that can really only be the way it is from a fracture and stretch.

          Personally I have needed *every single word* to familiarise myself with the 3D shapes enough to *test each match* trying to find alternate explanations for them.

          If you want my succinct work in progress summary, check:

          But in reality, for more information about the evidence, I will be linking each category of evidence to the relevant Scute verbose blog post, because you really have to see the matches to realise what amazing series of coincidences mission scientists are asking us to swallow to reject stretch as a possibility.

          Think of the verbose descriptions of matches as a tour guide to the thousands of unnamed but non-ephemeral ridges, plains, cliffs and dips with inverted equivalents about a kilometre away. You have absolutely no chance without a tour guide the first time, but then subsequent times, you will kick yourself for not having noticed them before.

    • Gerald says:

      Hi A.Cooper,
      regarding “the onion layers at Hathor are sliced through and nowhere near perpendicular to the head lobe gravity vector”, your interpretation appears to be flawed. These features are more readily explained as relics of shatter cones.

      • Marco Parigi says:

        Hi Gerald,

        If you were a good field geologist you would get this. If you follow the onion layers through Hathor, you would notice that they are there, perpendicular to the “shatter cone” ray lines or whatever they are. The strata lines are marked in red in the paper. The flatness of Hathor clearly slices through the onion layers – shatter cone or no shattercone.

        • Gerald says:

          Hi Marco,
          it’s not always clear, which paradigm you’re following, the “official” one, or “stretch”.
          Ok, so now with respect to the red marks in the upper right of the graphics
          ( :

          The field of gravity during sedimentation/accretion determines the attitude of the layers, not the remnants we see today.
          Part of the head lobe went lost durig the collision and by later erosion.
          A.Cooper’s argument remains flawed, no matter how to interprete it.

          • logan says:

            Hi Gerald: Perceiving accretive layering as ‘spray’ painting:

            Just a light spray from this side. Later a ‘coarse’ spray from this other side. Eventually making the ‘sprayed’ object ’roundish’ by averaging.

            Should take into account the differing kinetics of formative environment to ‘seeds’.

            Speculation is: Averaging takes precedence to Gravity. At least up to scale of Ducky.

          • logan says:

            Should think of Formative Environment as a multi-personality phantom. Every time you push on it, you are also separating it in all his personae.

            Formative Environments are subject to outside mass and energy waves. And, as Harvey says, this is molecular flow.

          • logan says:

            At the core or huge, huge nebulas, imagine of a dark, quiet place, free of the galaxy cacophony, where the finest of the dust remains, rests, for eons, ‘smelling’ of the ambient, adsorbing it. Here primigenial comet-esimals are born. They’re dark also, but not absolutely.

            This is a repost, just find better words 🙂

            This is cometary fiction.

          • logan says:

            A little more in this ‘spray’ layering idea: As being on those interminable tropical rains.

            Wind capriciously one direction or another. Light breeze coming directly to our eyes, washing our faces. Small drops weathering our cloths. Big drops falling almost vertically.

          • Gerald says:

            I like your cometary poetry.
            Accretion by cosmic sprayers
            forming cometary layers.
            Gently merging to a binary..

  • Bill Harris says:

    Andrew seems to have missed the principles suggested, particularly the last: Be Short. Kilobyte upon kilobyte of verbiage is not going to make a poor idea more palatable.

    At best, and most charitably, the stretch supposition can be described as “a stretch”…

    • A. Cooper says:


      The reply is the same length as the post that critiqued Marco’s and my methods. Isn’t that fair enough?

      We’re trying to draw attention to serious problems with the scientific methodology here. Just the problems in using the modelled contact binary as proof for CB theory warrants a thesis in itself. The calculations proving it should be eliciting an OMG moment for any thoughtful readers, not the intimation that it’s just so much drivel. 

      As it happens, I alerted Dr. Massironi to only half the problem with the model. The rest of it was put here for logan, but really should have been added to the comment above.

      Bill, this is a very serious issue. Please don’t make light of it. 

      • logan says:

        Not discarding the Stretch argument, Marco & Cooper. 🙂 Also know that you know more of Science discipline than Your late posts. Please make an effort to progressively detach your mind -which looks fine to me- from their contents.

      • logan says:

        This is the most stressed of recent orbits. More stretched will render 67P dimensions, as She abandons our neighborhood. There is no way to dismiss it.

        If not, Sorry.

        It’s the IDEA merits [or lack of], not you.

    • Dave says:

      Bill re Be short.

      Andrew seems to be dammed which ever way he goes.

      if he gives a short explanation, the cries are no evidence.
      If he details the data he has found, apparently he uses to many words.

      Maybe the blog is not the best way to present such a complicated idea, I think we should allow him some space.


      What on earth is going wrong with CAPTCHA, is anybody else struggling to get through the questions?

      • Gerald says:

        that’s the problem with all non-conclusive ideas. No matter how many words, it doesn’t get better.
        There have been similar cases in “established” science.
        Some very plausible initial ideas, some data providing moderate evidence, but no improvement with additional data.
        That’s mostly an indication, that something is wrong with the idea.

        Btw. Captchas work; good they aren’t too easy.

    • Marco Parigi says:

      Hi Bill,
      That’s the way target your criticisms to the theorist rather than the theory. Do you have any thoughts on the theory?

      • Gerald says:

        The theorist part of me would call “stretch” a hypothesis or a collection of hypotheses at best, not (at all) a theory.
        A (good) theory can be reduced to a small set of axioms, and all of the theory can be derived from these axioms by formal logic. “Stretch” falls miles short from that quality.
        There is not even a formal theoretical “stretch” model of a comet, be it applicable to 67P, or not.
        Sorry for speaking frankly, but that’s needed to be said with respect to actual theories.

        • Marco Parigi says:

          Hi Gerald,

          To rephrase, Bill was challenging the validity of what A.Cooper was saying by criticising the prose in which he said it. You are also challenging the validity of what he is saying, but this time by the descriptive word I was using to describe it.

          Am I right in assuming that it is beneath you to actually refer to what he wrote?

          • Gerald says:

            Hi Marco,
            I just don’t have sufficient ressources to dissect dozens of pages of mostly noise, and find out whether there are some hidden grains of truth.
            Better half a page of true evidence.

          • Marco Parigi says:

            Hi Gerald,

            I guess that answers my question in the affirmative…..
            You are fairly happy to refute EU nonsense – Time is not really the issue there, but time to find something to refute, which A.Cooper does make very difficult. When there is little to nothing to refute, you criticise it for being noise. My stub which I am gradually expanding on all the points of evidence in favour of stretch, has a more hierarchical structure, so that you can get an overall picture of how the evidence fits together, and as I fill in the individual points with short chapters, you can get more detail, and then more detail still within those chapters if you so choose. If there is anything that doesn’t make sense in the short form, just ask and I can improve on it…

          • Gerald says:

            Hi Marco,
            I appreciate your new approach.
            Hope it will eventually help to decypher whatever the comet tries to tell us.

  • Frankebe says:


    You state; “We should put aside our previous theories and models”

    …You also state that this mission : “…has the potential to decipher the origin and evolution of the Solar System.”

    Have you considered that the latter statement is itself based on one of the “previous theories and models”, and that this idea is one of the all-time great beloved theories about comets?

    …Just sayin’…

  • masanori says:

    Well, I never know how much (such) comments from public are welcomed by the mission team or are bothering them. But at least to me, this blog post looks like having connection with why I see Rosetta/Philae mission might be THE best space mission ever. Not only its science & engineering (from a view of me who is no expert of it at all!!). I’m talking about how this mission has been carrying general public along who have interests in the mission. It’s quite open, perhaps more open than all the space mission I have seen or heard. Open to even criticism on the mission. And quite notably, it looks like the mission has been doing this “live”, instead of preparing/pre-producing in advance a result they want & making/forcing this particular result happen. As if leaving what happens between the mission & public to natural process (or fate). To my impression this has happened to play a huge part on impacts which this mission has given/shared to public. So, thank you very much!!

    • Dave says:

      Re Public comments,

      I agree Masanori,

      The modulators have done a great job of letting the layman and various stds of would be scientists comment on the projrect, leading to a varied and lively debate that has maintained public interest. At some points even authors contributing, its been or is a blast.
      A fantastic well done to the team for allowing the mix while sifting out the normal personal attcks that are on some blogs- An example of how it should be done.


    • Marco Parigi says:

      Hi Masanori,

      This mission has indeed been fabulous and all of what you are saying is valid.

      However, did you see what Massironi did in point 2 there? To be thorough you need the best models, Osiris team gives me the best models to work from. You can’t have them because they belong to the PI, Holger Sierks. Therefore you cannot be right unless your on our team….

      I may be paraphrasing 🙂

      • Gerald says:

        Hi Marco,
        if you don’t like the ESA shape models, so why don’t you take Mattias Malmer’s?

        • Marco Parigi says:

          Hi Gerald,

          I’m not sure what you mean by “like”. I think Dr. Massironi was intimating that only the best, proprietary OSIRIS model would do to get reliable conclusions. Whichever other one I use will be prone to criticism of not being the most reliable.

          I see real 3D ridges and bumps in NavCam images that don’t show on any of the models. I want a model that is equivalent in resolution to the best OSIRIS 2D images. Say down to sub metre features or smaller. Then we could get somewhere. Perhaps naming more features than a couple of random rocks or gates.

          • Gerald says:

            Hi Marco,
            you can only draw reliable conclusions about surface features, if they are well-resolved.
            Otherwise you start interpreting matching jpeg artifacts (and the corresponding 3d artifacts).
            So, if you need highly-resolved 3d data, beyond Malmer’s detailed model, I don’t see a way to make much progress, before the OSIRIS data sets are published, or before we get NavCam images of the final spiral down.

          • Marco Parigi says:

            Hi Gerald,

            JPEG artefacts???? That makes a mockery of the stated resolution of the 2D images and has absolutely nothing to do with what I am talking about. Take the huge boulder Cheops for example. The Osiris team made a big noise about how the texture on Cheops was evident from the medium and high resolution shots. Shots taken at different times from different angles show the 3D nature of the ridges and bumps that make up the texture and the same ridges and bumps are evident on images taken at different times. However, even the best available model shows the whole of Cheops as a formless blob.

            Am I to presume that these texture features are possibly jpeg artefacts? No. It is just not within the scope of the model to show any features less than about 15 metres in diameter.

          • Gerald says:

            Hi Marco, I’ve seen both, true texture and several kinds of camera and compression artifacts.
            So I’d need a link to the original image, and the detailed features you’re talking of (including pixel positions, if possible), to assess what’s more likely, and whether it’s sufficiently resolved to make a decision at all.

          • Gerald says:

            … I’d should maybe add, that Cheops looks like a boulder which might have actually been displaced significantly, e.g. by an outburst or by a rockfall.
            It could be an old remnant of cometary accretion, as well, a remnant more resitant to erosion than its surroundings.

          • Gerald says:

            The smaller a feature the more prone to erosion the more short-lived, in general at least.
            So Marco, don’t rely too much on these small features when trying to fit fragments.
            More reliable is the stratigraphy, as e.g. exploited in the somewhat similar dendrochonology (, provided a sufficently large number of layers (strata) of variable thickness are available.

      • Gerald says:

        … and the ESA site with the shape models:

    • Sovereign Slave says:

      Well said and in total agreement, the public platform is much appreciated!

  • logan says:

    Incredulous? zealous? fair? [science is in principle a meritocracy] religion? doesn’t need to be proven? logical? [lots of things are illogical on natural sciences -just are-] convert? Your list of you one, or two or three is just too long. Law is not the right discipline to steep on Science. You have to have the humbleness to start from the start line. Even our best Scientists won’t have problem on helping you, just if you start on the start line.

  • Sovereign Slave says:

    Back to the contact binary theory for P67, I would like to know how it relates to finds such as that linked below, where 15 percent of near-Earth asteroids larger than 600 feet have a lobed, peanut shape. Seems like a pretty high percentage of asteroids, which should not have formed under the same conditions as contact binary comets according to accepted theory, yet have the similar two lobed shape. So, how did they form? Have to wonder too if they’d find on these asteroids very similar surface features to those that led to the contact binary conclusion being asserted for P67. Anyway, in the video, it shows asteroid 1999 JD6 as having two distinct lobes which look like a contact binary.

    • Sovereign Slave says:

      And yes, I know there’s the YORP effect theory, but here we have two very similar objects, yet the assumptions underlying the origins of each requires different mechanisms to explain their shape.

      • Gerald says:

        Sovereign Slave,
        good point! I share the feeling of a gap here.
        Why should comets form contact binaries by slow collision, and asteroids only by YORP?
        If we could rely on these two families of object being striclty disjoint, one could argue, that comets have formed in a benign environment in the outer parts of the early solar system, hence well-suited for very gentle collisions.
        Asteroids are closer to the Sun, hence more likely to be spun up by YORP.
        But this sounds a little too simple to my ears to be the whole truth.
        What about asteroids, which may just be “silent” comets, or relics of comets after loss of volatiles?

  • logan says:

    On formative environment issues:

    This pair of pillars at Carina Nebula, dino-head-and-neck form, very similar. As a coarse 3D pantograph copy.

    Speculating on them being ‘carved and modeled’ by the same ‘notes’ of the ‘music of the spheres’ 🙂


    On a imagination experiment: Have seen those 3D ‘explode’ graphs of gadgets? If making a 3D ‘explode’ of every grain of dust and single ice crystal of 67P Then plausibility looking something akin to this:


    On ‘wild’ use of’ imagination inner structure [even layering] is suggested at the surface of this beautiful nebula. [Just for inspiration, present are scale limits].

    Should be noted that this documents are part of Hubble greatest achievements [multi-spectral and HDR].

    The HST was built by the United States space agency NASA, with contributions from the European Space Agency, ESA.

    This is cometary fiction.

  • Dave says:

    Re soveriiegn slave – how common can rubber duckies be?

    Have a look at Kerberos circling Pluto, not much detail but looks like a twin of 67p
    Also circling Pluto hydra, looks like a rubber duck morthing into shape, but is it streching into a duck or shrinking into one, or are 2 chucks attempting contact binary.
    If two bodies on a tiny system can join togetherthen it must be a very common mechanism?

    • Sovereign Slave says:

      Or not the mechanism at all. Seems like if one understands basic underlying principles of something, it’s easy to explain other things. Rainwater is slightly acidic. Knowing that it’s easier to explain surface erosion. Water expands when frozen, also contributes to erosion. Accurate knowledge of something leads to straightforward understandings of phenomena that don’t then lead to the need for more complex theories to account for them. Accurate knowledge and understanding settles issues related to them. Yet here is yet another example of the need for 2 very elaborate, unlikely theories to account for duckies – one is that they are shaped by YORP (asteroids) and the other by contact and adherence (comets). The simple explanation is that they were/are shaped in the same way, and that there is still a misunderstanding of exactly what asteroids/comets are the prevents the recognition of the obvious. Seems this is generally the case, the need for more and more elaborate, complicated,, unlikely theories to support other widely accepted theories. This is because these theories seem to be more and more inadequate to explain more and more that is discovered.

  • logan says:

    Well, ‘Ducky-ness’ reign seems to extend…


  • logan says:

    Science of comets is simply taking a walk in the wild side:

    Ethyl alcohol and sugar in comet C/2014 Q2 (Lovejoy)
    Nicolas Biver1,*,
    Dominique Bockelée-Morvan1,
    Raphaël Moreno et al.

  • logan says:

    Before forgetting a pending issue, Matteo and friends:

    How do you interpret Ducky’s body at this photo

    Is it layering, crystallization or what? 🙂

  • Hugely enjoying this blog, and thanks ESA for a great job, a major step up from previous projects that were also top-notch technically, but where ESA didn’t manage as well to raise public interest. I hope (and expect) ESA will keep the bar at this level.

    I am not in favor of any specific one of the theories presented, just curious to eventually learn how it likely has worked for this comet. I hold Dr. Massironi in high regard and would be inclined to lean towards his view as an actual expert. Yet I can’t deny that his response is rather patronizing, expanding widely on rules that are truthfully rather trivial, rather than giving a substantive response regarding the “stretch” idea : what does he see as the strengths of this idea and what are its weaknesses?
    I would say the low-energy contact theory is by no means proven. That can’t be claimed just because a paper favoring this hypothesis passed a peer review. It is simple the best fitting of the two hypotheses considered. And no claim of truth or false can be made regarding hypotheses not scrutinized. Hence, the stretch hypothesis, left undiscussed in the paper, might still prove correct. (How likely I couldn’t say). One thing I learned in my career is that nothing has strengthened the build-up of my argument more than taking seriously any commentary by a sensible person. If you can’t convince that person, then that may be a warning your own material is not sufficiently solid. Dr. Massironi says he typically only reads peer reviewed material, and he takes a risk there.
    There is a lot to learn from visiting a conference where papers are not peer-reviewed but new ideas are put up for discussion, or from trying to really answer the comments and ideas from your pupils in class. Dr. Massironi probably does that, so why make this remark? It does not add value to the argument, and with it he breaks his own rules: it is not concise and it seems to serve to shield a preferred theory. It comes across as patronizing.

    Hope the discussion stays open and respectful, so we can all benefit from the outcome.
    (I suppose I am sort of a scientist, if a PhD in orbital mechanics counts for that, and being a regular author & peer reviewer and all).


    • Gerald says:

      The problem with stretch is, I think, that there is no available paper one could refer to, just A.Cooper’s veeeeery lengthy narrative site with lots of methodologic and geologic flaws, mixed with straightforward trivialities which don’t provide any evidence for “stretch”, since they can easily be interpreted by outbursts, erosion and sublimation.
      How could a scientist manage to get a reference to this through a peer review?

      The only option would be running models on a wide range of material properties, and look whether there is any non-zero probability to get the observed outcome.
      But at which point should these simulation runs be stopped, when all outcomes are negative?
      This combined with limited time and computer power, when other scenarios are shown to work.
      I doubt, that project scientists can spend endless time and money for scenarios which are close to hopeless.
      So it would be the job of the proponents of “stretch” to provide some reasonable and well-based approach.
      Otherwise the scientists run into the risk to be urged to buy the “Emperor’s New Clothes”.

      • Dave says:


        i think Andrew or maybe Marco has already addressed this, no need to waste time on computer simulation when we have no idea what the structure of the comet is, so models could be next to useless and right or wrong who could say.
        The comet is the model, if we can see a change in dimension from Osiris pictures on some datum points over time we should discover if the neck is stretching, stable or shrinking.
        If its moving at all, then that would be some extra data for any computor model, this then may give us some clue to the structure in the neck region to be able to construct some sort of realistic model.


      • Sovereign Slave says:

        Gerald, if Cooper and Marco had chosen to be brief in their assertions, in their own blog and this one, it is highly unlikely they would have ever been given any notice at all. Amazing to me that it’s taken this level of effort and persistence to have even gotten on any scientist’s radar, even if dismissively so. But then, as has been so hubrisly implied, if it is not in a peer reviewed publication, it is unworthy of consideration. Suffice it to say that there are non-scientist, equally intelligent folks out there that take a look at the practices, customs, and processes being accepted as standard protocol here that have serious doubts regarding it’s soundness.

        • Gerald says:

          Sovereign Slave,
          if Marco and A.Cooper had chosen to be brief and scientifically convincing, they would have had the best prerequisites to be considered.
          There is a sufficient number of readers here who could point project scientists to some work, if it is really worth to be considered.

          On the other hand, it’s impossible, at the moment, for scientists outside the Rosetta project to do their own, and independent research on 67P, or even verify the results of the project scientists, since most of the instrument data are still kept enclosed.
          So there is of course a risk of the thus far published results being biased, *because* a fair peer review doesn’t really take place.
          So, before this open review has happened, I’d take the results as probably correct, but nevertheless preliminary.

          • Sovereign Slave says:

            Good replies. Wish the papers acknowledged the same caveats of being preliminary findings and conclusions without the certainty assertions. I understand that there may be a number of n0n-scientific reasons papers are presented this way though – totally objective papers would not tend to get much notice or press.

      • Ramcomet says:

        Hi Gerald,

        Thanks for that view – you actually helped spotlight a very valid counterpoint to your own argument.

        The article about the paper admits they needed about a hundred Sims to get the one that produced a shape like Ducky. Wouldn’t one fairly call that cherry picking to find the Goldilocks Porridge they so needed to publish?… And the Sims took weeks EACH! Good thing they didnt stop looking at around “Ninety Nine Red Balloons”, (negative outcomes, to borrow a song title.)

        Another, (to me – so obvious), MASSIVE stumbling block of using that 3D Model: if you watch the video, over half of the head lobe is utterly destroyed /pulverized/ liquefied. And half of the body lobe is as well!


        To use that Goldilocks Model in the same paper as their images with Strata Vectors is utterly contradictory.
        Why? Because over half of the Strata depicted would no longer exist. They just can’t have their Onion Layers and eat them too.

        Frankly, the Strata Vectors point more to Stretch, as how I see them. Marco and Andy may indeed use them to help show this later on.

        I am not happy with this under rug sweeping. There is nothing “unambiguous” about this paper as claimed. There is nothing proven to send school children on their merry “non-Wegener Way”, (yet another valid counterpoint to the disservice of completely ignoring the thriving stretch hypothesis on ESA’s own blog). it is a disservice to make those claims just yet.
        You can keep saying the same things, how A. Cooper is way too wordy, (agree he was), etc. How hi is imagining things, (as an artist I see real matchpoints), But now I think a serious critique of THIS paper is in order. Seemed the peer review was a push-through party, to me anyhow.

        This paper/article should be retitled:

        ” How Comet 67P MAY Have Gotten its Shape”, since Stretch hypothesis was intentionally, even blatantly, left out.

        Meanwhile, all the words of advice are being well heard, so thanks to all for that. And although I am personally quite upset with some of the ivory tower snubbish attitudes here, I remain very, very grateful, as others have said for this blog and for the opportunity to mix it up with the Pros.

        • Gerald says:

          Hi Ramcomet,
          I’d think, that the paper seems to be essentially correct.
          But my feeling is, that the computer models may need some refinement. I can just guess at this point, that the compressive strength of the cometesimals might have been over-estimated, possibly due to the models usually using incompressible spheres as “finite elements”.

          Another possible issue might be an over-estimate of local relative velocities in the protoplanetary disk.

          Accounting for these two factors may improve the probability of contact binary formation considerably.

          That’s a diagnosis from the distance, so I may well be wrong, and these points have already been considered.
          If they have already been considered, your scepticism would be justified. But in this case I’d still prefer a mostly erosional scenario, e.g. starting from a Jacobi ellipsoid (that’s a somewhat bar-shaped triaxial ellipsoid), which later collapsed under its own weight after loss of material in the neck region. I doubt, that all these erosional scenarios have already been investigated.

          After ruling out these “traditional” scenarios, one might then investigate “exotic” scenarios, like “stretch”.
          But as I said before, I think, that the most likely way to ressolve the remaining issues, will be refining the computer models of the material properties and the protoplanetary disk.

          • logan says:

            The ‘Third Object’ Saga could bring closer plausibilities of time and space coincidence. Also of ‘cementing’ material and a minimal amount of attracting gravity. Other clues apply.

          • logan says:

            Both binary lobes looks quite hurt, has been at or passed trough a crowed place, as you comment, maybe young planetary disk(s), as is dominant argument.

            Was our young Sun as energetic as today?

          • Ramcomet says:

            Hi Gerald,

            Well I guess, if my reasoning, along with Andrew and Marco’s blogs, have ANY concern at all for the team, then a square peg’s corners can be sanded off, to eventually fit the round hole?

            Overstated, but this is what your response sounds like to me, a layman of course… Let’s make another 99 model balloons, after the recipe is adjusted, so the Binary square peg can still fit the round hole.

            I know that is not entirely fair, but do you see what I mean?

            This is all because they present that paper as unequivocal FACT. Way to early!


    • Marco Parigi says:

      Hi Gerald,

      I’m not sure if Michiel will weigh in on this issue of finding a model solution before something is considered possible.

      To me it does not follow from the definition of the scientific method. Like with Climate models, there is room to doubt the models based on their lack of predictive power. Much worse in this case because the models are all theoretical and cannot be readily verified empirically. At least with climate models, we can measure future climate and compare with model outcomes eventually.

      I accepted from when I first settled on stretch as a solution I was confident in, that the bar was set unreasonably high. However, having had a look at Rosetta and Philae’s mission profile, I believed, and still do, that the equivalent of continental drift’s mid ocean ridges would likely be found before the end of the mission, so the point would be moot.

      • Gerald says:

        Hi Marco,
        I’m confident, that we’ll see clear evidence for significant surface changes due to erosion/sublimation as soon as Rosetta gets closer to the nucleus.
        If old matches (which I still don’t see) will have vanished due to cometary activity, or new ones emerged (in your or A.Cooper’s eyes), this should question the validity of the matching method.

        If a mid ocean ridge equivalent can be revealed, I’ll be happy to have learned something. But I’m realist enough to seriously doubt.

    • Ramcomet says:

      Where is my “like” button? Perfectly stated!
      Thanks very much.

  • logan says:

    Corollary: Expecting Silicates to be relevant among Ducky’s dust.

  • Dave says:

    Sovereign slave – or not the mechanism at all.

    My question to you was tongue in cheek, so many similar shaped bodies flying around, you would think there would be a different solution other than a gentle kiss, that is statistically inclined to produce duck like shapes.

  • Dan says:

    It’s very rich that some call EU theories nonsense when they equipped their landing craft with ice harpoons to make it land on a imaginary “dirty snowball” comet. Yes, the one that turned out to be nothing of the sort and a of rock. The rocky looking rock 🙂

    The comet has turned out to be far from what the standard model predicted in almost every way and some of the explanations from ESA shows how difficult it is to detach one self from those wrong assumptions as they try to somehow get back “inline” to the standard model.

    These days “Back to drawing board” is the new standard model of cosmology.

    • Gerald says:

      The purpose of exploration is finding something unknown.

      “change of the target comet has a major impact on the Philae landing safety, since the
      expected touchdown velocity is much higher than in the case of P/Wirtanen (the original
      target of the Rosetta mission), due to the much larger size of P/Churyumov-Gerasimenko.
      Some hardware changes have been implemented, to increase robustness at touch-down.
      However, the safe landing remains highly sensitive to actual nucleus properties, largely
      unknown at this time.”, Folie 54

    • Gerald says:

      … cosmology is -roughly speaking – about the geometry of the universe on large scales.
      That’s just marginally related to 67P. The observations of 67P don’t constrain the validity of established cosmological models, not obviously, at least.

  • Gerald says:

    Hi Marco,

    I like your answer, although I disagree in several points:
    – The Whipple model has been modified from a dirty snowball to an icy dirtball, so I wouldn’t see this as axioms beyond the model itself, but as inferred from observations, of course with large error bounds, to be seen in the context of an unsolved conundrum in the times before the Whipple model.
    – The (modified) Whipple model isn’t sufficiently powerfull to predict all the detail you’re missing. This doesn’t mean, that it’s wrong; it just means, that it’s incomplete.
    – Onion layers etc. need to be derived from the accretion process, and physical conditions, like temperature, composition, rotational state, etc.
    – Re untestability of the accretion scenarios: I’d do it the other way round, and infer the accretion scenarios consistent with the observed properties of 67P.
    Going the axiomatic way, i.e. starting with a set of axioms and hoping the observations to fit, is close to impossible, since although the rules are rather reliable laws of physics, the initial conditions are zero probability to predict correctly without observation, and even if, besides quantum-mechanical Heisenberg uncertainty, we get deterministic chaos limiting the range of a purely axiomatic approach.

  • Marco Parigi says:

    Hi Gerald,
    The smaller a feature the more prone to erosion the more short-lived, in general at least.
    So Marco, don’t rely too much on these small features when trying to fit fragments.
    More reliable is the stratigraphy, as e.g. exploited in the somewhat similar dendrochonology (, provided a sufficently large number of layers (strata) of variable thickness are available.”.

    Erosion appears to be coming from within the comet, in the same way that when I breath out water vapour there is a kind of erosion of my body but it doesn’t affect my facial features which a facial recognition system would recognise.
    I’ve been too busy researching the meteors coming from comet TB145 to get too upset with Not being able to keep my ongoing 67P conversations moving…

  • Gerald says:

    Hi Marco, your facial features remain intact as long as you replenish the lost water by drinking.
    67P is lacking this privilege.
    So, subsurface erosion eventually reshapes the surface.

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