67P/Churyumov-Gerasimenko. A single body that’s been stretched. Part 6

Incorporating matching structural ridges into existing matches (orange dots)


Annotated photo of the shear line where the head broke away from the body, as described in parts 1-5. Click for hi-res. Zooming is advised.


[There are a couple of anomalous black blobs that appear to be artefacts of dots mistakenly placed and then erased. These are on site A (the flat crater) and on the neck. Please ignore these]

Green dots: shear line as described in parts 1-4

Blue dots: show matching ridges across head and body lobes. The long blue ridge across head and body overlapped at the scalloped triangle (blue dot in 2nd photo below) and incorporated the pushed-up ‘gull wings’ along that short distance. These gull wings are described in part 5 and match the gull wings directly above, under the head (not visible here).

Yellow dots: show how head cove fits to base

Red dots: point-to-point matches

Light orange dots: ‘geological’ or structural shear ridges (head lobe shows these with one large dot either end). These are not the actual shear line but ridges that were exposed by the head uplift and the uplift of two hypothesised adjoining slabs that drifted away. However, because the head uplift caused them to be exposed, the main shear line does follow both ridges for a short distance- the rest of their extent was covered by the slabs. The two ridge lines on the head match the two on the base. However this is tricky to visualise: since the head has to be tipped back 30 or more degrees to seat down on the body, it is the bottom ridge line on the head (as viewed from this shot) that fits to the top ridge line on the body. Similarly, the top ridge line on the head fits to the bottom ridge line on the body. There is also a small anticlockwise rotation needed for them to fit.

Brown dots: supposed shear line running in ‘mid air’ across missing slab area. This would be the third and largest missing slab.

Fuchsia dot: next plausible match point (mirror point on head not in shot).

Below is a similar annotated photo from a different view. This excludes the orange dots for the structural ridges since these aren’t thrown into relief as much. It also excludes the fuchsia dot (off frame to right) but includes a large blue dot to denote the centre of the scalloped triangle. You can see the two circular slurry piles which were ejected from under the scallop and which pushed up each gull wing 20 metres or more (wings only just visible from this angle). The gull wings correspond to the wings under the head which again are not visible. However, a third tier of wings is visible here. They are next to the first green dot on the head and appear to match roughly to the scalloped triangle. That is because the three tiers of wings were stacked loosely like puff pastry, one on top of the other. The true match to the scallop is pictured side-on in part 5.

The three green dots on the head correspond to the first three green dots running along the back of the ‘rectangle’ that incorporates the scalloped triangle. This short section is the subject of part one with the rest of the green dots dealt with in parts two and three.


Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0



4 thoughts on “67P/Churyumov-Gerasimenko. A single body that’s been stretched. Part 6

  1. To quote Sherlock Holmes “When you have eliminated the impossible, whatever remains, however improbable, must be the truth!”
    Having gone through various replies to tweets of this watertight photogrammetric matching, the common responses are that, essentially, stretching is improbable as a general explanation of various comets’ bilobed shapes.
    As you said, the probability of these matches happening in the third dimension and across many points just by chance is essentially zero. This rules out all mainstream ideas, and most outlandish ideas about how bilobed shapes form when applied to 67P C/G.
    The only thing left, despite well meaning protestations to the contrary, is stretching. And if it is proved certainly the case for 67P C/G, then why not for other similarly shaped comets?


  2. Hi Andrew, the following link is to an article about the bilobed shape research. http://www.slate.com/blogs/future_tense/2014/12/31/why_rosetta_s_comet_is_shaped_like_a_duck.html
    It mentions the “layering” we have talked about here and elsewhere. It presumes the strata are parallel and go through the whole body lobe, while I got the impression they were more concentric than parallel. What is your opinion of the strata? Concentric or parallel?
    The article (and underlying AGU presentation) explains both the head and body to have strata of the same type, but that they do not line up in the way they do on each individual lobe. All that means to me is that the head and body lobes are somewhat independent and out of alignment, which is what we talked about in the stretch, the head tilted back roughly 30 degrees. A collision also does not explain the circular cross section of the neck.


    • Thanks Marco

      That was an interesting read. I’m lost for words to be honest. How they can see all this stuff and not see how the stretch theory explains it all is quite astonishing. To see the parallel strata in the base, then see the same thing in the head and actually use that as proof they are different bodies shows that they are totally blinkered. That observation should lead to the immediate eureka realisation that the head has tilted (as you say). 

      As far as the onion versus straight layers is concerned, I only got as far as proving or trying to prove that the layers next to site A were parallel to it. That was quite a small part of the comet so it wouldn’t prove either theory. However, since my Part 6 linked the very straight head layers to the body ridge lines, I can only assume that the body layers are indeed straight, as they say. What appears to contradict this are the plateaux on the body which give the impression of a polyhedron which is an approximation to layers on an onion. Nevertheless, I believe that these may simply be due to general turnover of the surface and dust deposition. That process could be masking what would otherwise be the outcrop of straight fracture lines like those very visible ones on the head. 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. What I don’t trust is their interpretation of those observations. 

      Another case in point is their supposition that the asymmetry in the neck fractures point to the neck having been made up of different elements apparently jumbled together. To me, this portion of neck appears to be the part that was heated the most and underwent Robin Sherman’s ‘cryovolcanism’. It has all the traits of a substance that has been melted down, extruded and reset. The cracks are there because the cooled, crystalline residue has the consistency of dry mix concrete: strong under compression and extremely weak under torsional stresses. Very minor forces on the head would easily lead to such cracks and their asymmetry would be down to the random nature of the original cooling process. I would even suspect that the gravitational changes brought about by loss of material on the body over several orbits could induce the head to tilt up or down by a metre or three and so induce the cracking process. 

      As for the head crashing gently into the neck, it presupposes that the body was floating around for aeons sporting this inexplicable protuberance of a completely different structural nature- which then hardly collapsed at all as it received the head lobe which happened to fall directly in on top of it from above. 

      I’m in the process of replying to your Roche pass comment but I’m a bit behind. I should be ready to  post Part 7 tomorrow as well. 


      • I am just waiting for the penny to drop. Admittedly, the research and observations that the article is based on, were made at around the time we just started talking about it on the Rosetta Blog. Still, I am not sure why they wouldn’t keep an ear out for alternative theories on the blogosphere, or even see the evidence independently themselves. I suspect that the layers appear parallel because site A and the layering under the body lobe are coincidentally parallel. Other evidence of layering on the body lobe is not as convincing. My hunch is still concentric despite the observations.


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