67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 38

THE GULL WING DELAMINATION ON THE BODY 
   

Dark green- five sets of delaminated gull wings on the body (denoting four distinct rifts). Each pair of gull wings has one dot for each of its curve midpoints. The classic set at the end of the cove seating (see Part 36 and before) is the third or middle set in this view. This is easier to see in the more elaborate annotations below. This is a pure, pared-down version so as not to distract from the main subject of this post which is the delamination itself and the direction of stretch vectors. 

Light blue- these are tell-tale rift lines that join to the five sets of gull wings. They, of course, had to delaminate as well, meaning that this delamination process was planar. In other words, it involved lines delaminating across an area as opposed to points or quasi points delaminating along a single line. The five sets of gulls wings could be described as the latter, but they are simply part of the former. So they define a line along the edge of the area swept by the planar delamination of the ridges. And of course, the gull wings are really just part of the ridges anyway. They just happen to be more recognisable, have a colourful history and garner more press in this blog for that reason. 

Photo 2- a top-down view of the five delaminated gull wing sets for orientation purposes. 

 
Dark green- the five sets of delaminated gull wings on the body.

Yellow- the set of gull wings on the head lobe cove that matches to the middle set on the body. Notice how the right hand yellow dot isn’t on the shape that looks as if it matches to the shape on the body whereas the left dot is. That’s because this shape is the upper, second set of gull wings on the head (and third vertically delaminated set including the set on the body). It obscures almost all of the true head rim match below it, which is the first head rim set of gull wings. Just that tiny amount of the right hand wing is showing itself. The other four sets of gull wings on the body don’t have discernible gull wing shaped matches that are mirror-matched to the head rim. That’s because the first two sets by the horseshoe crater are just remnants of the third set and the fourth and fifth sets along the Babi shear line towards Aker are just vestigial bumps because they delaminated so far back. However all sets are surrounded by a multitude of mirrored matches from head rim to body (Parts 1-8 and 18).

Photo 3- the ESA regions map for 67P. 

 

BACKGROUND

In previous parts we’ve only ever looked at a single delamination of the gull wings, creating two matching sets. Those are the second and third sets from top-right in the header. That was where the classic set tore away from the side of the horseshoe crater and slipped along the shear line. By doing so, the sliding wings opened up the shallower crater above and to the side of the horseshoe crater. And the slide or rift along the shear line opened up the curved fissure that fed the single hole which then delaminated into three. The hole delamination occurred during the head stretch or herniation from the body and those three holes stayed with the head lobe after the main head shear. 

Now we’re adding three more sets of gull wings. That betrays three more delaminations, making a total of five gull wing sets and four delaminations. Four sets are definitive matches and the fifth is highly compelling.

For numbering purposes, we’ll call the top-right set of gull wings the first set. It’s the set adjoining the Site A rim. So the fifth set is at bottom left. The second set would be the set that the classic set delaminated from on the horseshoe crater rim. This set then slid back from the rim in a different radial direction from the classic set, more in keeping with the monolithic slide (Part 33). The classic set, which matches to its vertically delaminated twin on the head rim, 1000 metres above, is the third set. And the set at the other end of what was dubbed the ‘green rectangle’ (Parts 5,7,8) is the fourth set. The area between the third and fourth sets corresponds exactly to the area matched to the head lobe rim underside in Part 1. The area between the fourth and fifth sets corresponds to the area matched to the head rim in Part 2. 

Just to be clear, the matches in Parts 1 and 2 were mirrored matches from body lobe to head lobe while these lateral delaminations in this post are translational matches like spreading a pack of cards across a croupier’s table and seeing the parallel long edges of the cards matching. That’s the same type of match as the red triangle recoil. It means the cards must have delaminated across Babi as shown in the header before their intervening mirror matches on the shear line could be matched to the head rim. That in turn means that Hathor must have been undergoing exactly the same stretching and delamination as the green dots in the header. It had to do so in order for the mirrored matches to be so faithful after the lateral delamination had occurred. Hathor is the cliff on the head lobe underside (omitted on the ESA regional map). It was clamped to the body prior to shear and so it’s not at all surprising that Hathor has to have stretched in the same manner as the header photo dots and in lock step with those actual green dots it was clamped to. Indeed, this was touched on in Part 37, regarding the terracotta stepped feature that is very evident in Hapi and mirrored on Hathor a long way down under the head rim. 

So the gull wing delamination in the header indirectly betrays a substantial sideways stretch as you look at the Hathor cliff, the underside of the head lobe. That will further our understanding of the dykes running up the Hathor cliff in due course. The dykes were introduced in part 8.

As well as the card-spreading trick it would be as well to bear in mind that three of the ridges fanned out so their ‘card edges’ aren’t parallel. So a fan analogy applies as well as the card-spreading analogy but they are topologically identical: planar, translational delaminations. 

Four of the five ridges exhibit mini matches as if the original pack of cards had been sculpted along its edge with bumps and dips before being delaminated. 

THE GULL WING DELAMINATION IN DETAIL 

In the header photo, three of the light blue lines arc from a single axis point on Babi. Those three lines lead to the middle three sets of gull wings and show definitively that those three sets delaminated laterally from each other. The middle set of these three is the classic set at the end of the cove seating. These three lines have several ups and downs along their length that can be matched as mini matches. These can be seen more easily in the unannotated version. There’s a small amount of foreshortening and stretching of these mini matches but they are clearly there. That’s why these three sets of gull wings and their ridges are definitively linked. 

The first gull wing set, kissing the Site A crater rim, has a blue line leading to it as well but that line has been intentionally detached from the main, sharper, shadowed ridge coming up from lower down in Babi. That’s because it’s a slippage rather than the neat arcing round from a single axis that characterises the other three. So it’s a slipped card rather than an arced fan leaf. Two of the three fan leaves arced off on one side of the main ridge, creating the fan of three and this first one slipped the other way from the main ridge and stayed nominally parallel rather than arcing on an axis. And yet, remarkably, the very same mini matches can be matched to this slipped ridge as for the other three, although they’re slightly more stretched about. Therefore the first set of gull wings is also definitively matched to the other three. 

The first ridge line also has its own mini ‘fanning out’ delamination, which is a short arcing on an axis from halfway along (not annotated). That means there’s a mini fan of two or even three short ridges for the first two gull wing sets as well as the slippage. But the slippage component for the full length of the first and second ridges looks to be overwhelmingly dominant with just this small, sympathetic fanning. 

So if the first four gull wing sets have been definitively matched via their ridges, that leaves just the fifth set. That set isn’t so compelling when trying to link it via ridges. A tentative line has been drawn as a preliminary indication of what is probably a slipped ridge from the fan of three but it can sometimes take several different views under different lighting to start seeing matches. The fifth gull wing set nevertheless looks highly compelling in the side view photos below.

And the light blue ridges aren’t the only way of matching the fifth set to the other four. This set also exhibits what appear to be a similar pair of pimples to the fourth set (next to their pairs of green dots). The pimples on the fourth set are definitely pimples and not rocks. Those on the fifth set haven’t been confirmed as pimples and may be rocks but it would be highly coincidental if they were rocks. And the real clincher is that both sets exhibit three faint, rectilinear features to the lower left of their green dots. That’s also in line with the delamination direction, which is promising. 

SIDE VIEW OF THE GULL WING DELAMINATION 

Photo 4- side view of the gull wing delamination. 

 
Dark green- (zoom needed) the gull wing sets as in the header. The first set is on the right and the fifth set is on the left. 

Light blue- the ridges as annotated in the header. The exact axis of the fan of three was difficult to pinpoint but it’s very close.

Beige- these two dots are below the third pair of green dots which denote the classic gull wings. The beige dots are kissing the front, central bases of the two slurry piles that oozed out from under the gull wings. Those two piles are what pushed them up into gull wings in the first place. You can just about see the concentric ripples in the nearer pile. These are clearer in photos in Part, 5,7 and 8. They’re also visible in the orientation photo above (photo 2), especially the pile that’s nearer in this view. It’s a near-perfect semicircle with concentric inner semicircles, like a dollop of thick custard or slumping concrete. 

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The first three gull wing sets in photo 4 are discernible as pairs of wings and so have pairs of dots. The fourth and fifth are more in profile so they have one dot each. This is in keeping with the fact that the first three sets got dragged back towards Ash (towards us in this view) by the monolithic slide (Part 33). The first set got yanked the most because it was probably attached to rock C which was, at that time, part of the monolith that slid. The second set was on the horseshoe crater rim so it was yanked a little less and pulled along the main delamination force vector a bit more. And the third set, the classic cove set, was being yanked partly towards Ash but mostly along the main delamination vector, which is along the shear line. The last two sets were further from the monolithic slide so they kept faithful to the predominant line of the delamination vector along the shear line. Also, being the two furthest removed from the first set, the fourth and fifth sets are barely discernible as gull wings. They’re more like wide bumps with two pimples on top.

Photo 5- the header photo with additional annotations. 

   

The header was left uncluttered so as to focus on the gull wings and their ridges. These additional annotations add context.

Dark green- five gull wing sets.

Light blue- delaminated ridges linking the gull wing sets.

Dark blue dot- a single dot showing the current north pole.

Brown- two dots. The one next to the blue dot is the paleo pole preliminary adjustment as described in Part 37. The one to the right, up the rim of Site A is the estimated position of the actual paleo pole during the initial stages of head herniation. Its positioning is also discussed in Part 37. 

Pink- one dot. This is sitting in the middle of the horseshoe crater.

Fuchsia- these two dots denote the tips of the delaminated India shapes (Part 37). They slid by the same distance as the distance between the second and third gull wing sets. That’s because they are part of that delamination, i.e. the slide from the horseshoe crater rim to the classic gull wings position. Part 37 showed the India shapes from above. This lock-step slide with the gull wings along the small curved section of the shear line is quite clear in that photo.

Yellow- the cove seating which matches to the present-day cove on the head lobe. 

Red- the three dots next to the pink dot show rock C’s seating from which it broke away. Rock C used to form the top part of the back rim of the horseshoe. The two dots to the right show rock C itself.

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Photo 6- this photo is as photo 5 but with head lobe annotations added, along with the fissure for the 3 delaminated holes on the head. Also, an interesting mini match. 

   

Yellow- the upper-left line is the bottom rib of the middle scallop in the cove. If the head stretch and herniation are reversed, this second scallop collapses onto the first one, which means this yellow rib collapses onto the bottom rib of the first scallop (which is the head rim itself). The head rim has a similar but subtly different profile to the middle scallop rib. But when they are clamped together, their combined profile marries to the yellow curve on the body lobe at lower-right.

Light blue on head lobe- these two dots show the middle and upper delaminated holes that slid from one lower hole on the first scallop. Each one is next to its respective scallop of the three scallops. The bottom scallop and its hole are half out of sight, half in shadow so the bottom hole can’t be seen. That hole is really just the gas-scoured base of the original hole and not discernible as a hole. The three nested holes were originally kissing the yellow curve on the body along the line where the slate blue line runs. 

Slate blue- this is along a section of the yellow curve on the body. This is the seating of the delaminated hole. Or rather, the hole was just above this line which was the fissure opened up by the slide of the classic gull wings from the horseshoe crater rim. The near end of the slate blue line is kissing the gull wings that slid because the fissure is defined by the slide. Just below this near end, you can see a shadowed area at the bottom of the shear line cliff (not the darker shadow that the line is touching- that’s the gull wings). The shadowed area at the bottom of the cliff is curved and has a small rib halfway up. This curved recess may be the other half of the longitudinally sliced dyke on the Hathor cliff that runs to the scoured hole base described above (and in Part 36). It’s in exactly the right place, completely constrained by all the other matches around it. It doesn’t look as if it extends up far enough because it should extend to the yellow line. However, the photo is deceptive. Behind the dark shadow of the gull wing (its left wing in this view) there’s a fairly deep recess. It looks as if we can see everything with the shadow being divided from the brighter part by a defined ridge but the left gull wing hides the channel.  

Bright blue- these are short lines at the end of two of the three fanned-out ridge lines. They’re mini matches and, along with the tips of the bright blue ridge lines, they form a triad of parallel lines. So these two ridges, from their shared axis point to their tips look like tridents. Its highly recommended to look at the unannotated version to see this because the dots completely obscure the feature. The way in which the lower trident’s prongs are twisted round anticlockwise by 90° and the staff stretched is entirely consistent with the stretch vector of the delaminated gull wings. So much so that you can visualise how the fine movement of the slide must have played out, like a movie. 

CONCLUSION

The five sets of gull wings clearly delaminated in the comet’s long axis direction, along the shear line and away from the pole. This particular direction of stretch is wholly expected. It’s both radial and straight down the long axis. Or, to be exact, parallel to the long axis running through the core a few hundred metres below. And this spectacular mode of crustal stretch via multiple delaminations has already been seen occurring at the south pole, on the red triangle and with the main sink hole on Site A. But you can have only a single line running both down the long axis and through the north pole point. The whole delaminated area obviously can’t do that. But the five sets of gull wings form a quasi line with almost no area. They spread along that long axis line and radially from the pole, give or take some pushing about that was probably after the delamination anyway (due to the monolithic slide). But their accompanying ridges are spread down into Babi and fan round across the delaminated area. There’s a lattice of stretch vectors at play, with any particular point in the layers yielding only partially to its local, surface, radial vector from the pole. That’s because it was also being dragged along as part of a delaminating layer. And the tensile force direction for the delaminating layers was dictated by the long axis stretching. That is, the long axis-dominated core stretching under the crustal layer. The gull wings are a special case because they’re sitting along that line which would give them the same force vector whether radial or core/long axis-driven. But the further down Babi we go, the more the ridges were torn (literally) between the core-driven long axis stretch delaminating the crust in nominally parallel layers and wanting to do the simple radial slide. The radial slide was at a different angle, in fact, varying angles to the long axis delamination direction. This will be looked at more in the next part and involves the idea of the entire rotation axis being brought into play, as it should be, for the core.

We shall see that for the Babi crust, the radial force vector won out in the end but the initial delamination of the layers left its signature over the whole region in spite of this. This has implications for the morphology of Babi and, indirectly, for the missing slabs A and B, which are missing from site A and Babi respectively (Part 9). That will be addressed in the next part. 

PHOTO CREDITS:

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

To view a copy of this licence please visit:

http://creativecommons.org/licenses/by-sa/3.0/igo/

All dotted annotations by Scute1133.

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67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 37

 

SUMMARY OF RADIAL STRETCH VECTORS AROUND THE COVE/HORSESHOE.   
 
This post is one long narrative key to the header photo. It summarises the stretch vectors and crust sliding/delamination presented in Parts 31 to 36.
References to up, down, left and right are with respect to the ‘upright duck’ configuration as shown in the header photo i.e. with the head lobe on top and body lobe at the bottom. 

Blue dot- the north pole. The north pole is where the rotation axis pierces the comet’s surface. It pierces the other side at the south pole. You could imagine extending it out both ways and twiddling it in your fingers to rotate the comet. In this view the extended axis passes a little to our left and somewhat below us. Rotation is the head at top-left downwards and body at bottom right upwards. 

Upper brown dot (next to the blue dot)- an adjustment of the current north pole. It’s a point that’s swivelled by the same angle from the blue dot as the paleo rotation plane is swivelled from today’s rotation plane. See the appendix at the bottom of this post for the workings to arrive at this point. This doesn’t give us the exact paleo pole position for when the head was on the body but it constrains its possible original position to being somewhere on a line from this point, down the rim of the Site A crater. That’s because the crater rim is in the same plane that the head lifted, which was almost vertically above the horseshoe. This means that the head dragged the centre of gravity up through this plane as it lifted. That in turn means that the z-axis of the comet’s rotation rose up within this plane. This axis lift was almost a pure, single dimensional, translational lift upwards with very little swivelling about the centre of gravity. It would be like lifting a barbell (rotation axis) using one hand gripping the middle (the centre of gravity) and successfully raising it while keeping it horizontal- and with no swivelling about. The extent to which the rotation axis did swivel is betrayed by that short distance between the blue dot and brown dot. The swivel was a precession about the long axis of the comet, which was probably brought about by the head lobe slice (Part 20) which in turn caused the head lobe itself to precess anticlockwise about the long axis by about 15°. 

Lower brown dot- this is an estimated position of the actual paleo north pole. That would be the north pole when the head was seated on the body but starting to herniate from it. Seeing as the pole is the point where the rotation axis pierces the comet, it means that when the axis was dragged up vertically in its translational lift, the paleo pole, where the axis pierced the surface was also dragged upwards. If you reverse the head lift and seat it back on the body, the current north pole dot would initially drift left towards the top brown dot (as the precession that happened during head lift was reversed) and then drift down the Site A rim to its estimated original position. In fact, it would drift down as well as left even in the initial stages of reversal because both precession reversal and axis drop would be happening at once. So it wouldn’t actually drift through the upper brown dot but left and under it until it was on the line between the two brown dots. And then it would be travelling straight down along that line which is the crater rim. 

Red arrows- the tensile stretch vectors. They’re pointing predominantly radially, away from the cove/horseshoe formation. That’s the same as saying that they point radially away from the current north pole because the north pole is right next to the horseshoe crater. And the paleo pole would have passed through or very close to the horseshoe crater during head lobe lift so wherever it was located before or during head lobe lift, it was close to the central focus of the radial vectors. However, during herniation, the paleo pole wasn’t quite the central focus. That might be explained by the ‘pie-shape effect’ explained in Part 36. That was where the big outer masses of crust attached to inner portions would rip those inner portions out regardless of their being slightly off the radial centre. In other words, these larger attached chunks would dominate over the neat geometry of everything sliding out like pieces of cake with their tips all kissing the north pole. That would be too much to expect. Instead, localised random fractures around the pole would succumb to the forces exerted from the larger, attached masses at the extremities, which were also under a greater centrifugal force. There are some missing arrows, off-frame to the right across Seth that were presented as part of the lattice in Part 31. Seeing as a similar number are missing to the left, off-frame and yet to be presented, this photo is showing just those central vectors that are clustered closer to the cove/ horseshoe crater. This picture will be widened and updated once Babi is dealt with to show all the stretch vectors across the body. And eventually the whole of Ma’at on the head will be included.

Fuchsia- the two India shapes that delaminated, one from the other. This slide opened up the curved fissure which fed gases to the 3 holes that sat on this spot (and are now on the head lobe). Also, there are two fuchsia V shapes to the right. The first is a delamination, the second is a straightforward tear of the lower onion layer. They are both thought to be related to the India shapes. This photo doesn’t do them justice so better photos will be presented in future. 

Terracotta- these steps were first presented in Part 7. They must have stretched with the head because they match to similar steps on the underside of the head rim i.e. on the Hathor cliff. There are other close up photos that show them as being at least 5 very consistently matching steps. There are two well-defined ones here and two less well defined and it appears the one in the middle is whited out. But this is enough to show the direction of delamination betraying the stretch vectors. 

Pale yellow- a new, large-scale slide. 

Bright yellow- the lower line on the body is the classic line of the cove when it sat on the body. And the two lines on the head show how the middle scallop would collapse onto the bottom scallop if the stretching process were reversed and the head seated back how it used to be. 

Red- at the right hand end of the bright yellow lines. These simply denote the ends of the top and bottom ribs of the middle scallop in the cove and where they would have sat on the body. Notice how the bottom pair are closer together and the top pair wider apart. That’s because the head tipped up somewhat during the lift so the cove is angled up a little more towards us. Incidentally, the head tip wouldn’t run counter to the idea of the rotation axis staying horizontal and not swivelling. That’s because the head tipped (and swivelled) largely about its own centre of gravity during the rise and the rising rotation axis was only responding to the separating centres of gravity of head and body.

Larger dark green- on the body: the two end points of the ‘India shape’ slide which opened up the fissure and by doing so started opening up that shallower crater above the horseshoe. So the green dots mark the width of the fissure. On the head: these two green dots would sit on the two green dots either side of the fissure below. They also correspond to the width of the two delaminated sets of gull wings on the head (see Part 36). Since they’re the same width as the fissure they also mark the width of the conduit through which gases passed to the original hole that delaminated into the three on the head (Part 36 as well). And of course, the fissures on the body and head are the same width as the holes. The first hole in the bottom scallop is really just the scoured base of the hole before it delaminated into the two obvious holes above. However, in this picture, it always looks more like a hole due to the lighting. And now that we’ve established the actual scoured base location in Part 36, we know this apparent hole is actually the conduit leading to the scoured base. The base is actually tucked into the top right corner of this neat-looking ‘hole’ which is really the flat, scoured conduit. That’s how easily the lighting can fool us. The tiniest bit of relief shadow at top right corner tempts us into thinking the whole area is a hole. Foreshortening is another issue here because the scoured base is sitting in the bottom scallop and almost hiding under the middle scallop rim. 

Small green- these dots run along the gull wings on the body (contiguous with the end of the yellow line) and also along the seating from which they delaminated. That seating was originally next to the rim of the horseshoe because we established that the gull wings were attached to rock C when rock C was in the horseshoe. It appears that even the seating itself slid away from the pole in sympathy with the rock C slide that opened up the horseshoe (Part 33, the ‘monolithic slide’).

APPENDIX- THE PALEO POLE ADJUSTMENTS

This appendix concerns the brown dots representing the paleo north pole in the header photo. It explains the adjustments that were made, using the current north pole and knowledge of the current and paleo rotation planes, to place them.

The adjustment was done by observing the distance between the current plane and paleo plane paths through the four coloured body matches facing Anuket (coloured matches: Part 24). The point of measurement was at a similar distance from the centre of gravity as the north pole point. And the centre of gravity is at the origin of the 3-axis reference frame. Seeing as the north pole swung by the same angle as the rotation plane, the distance of that swing is the same as the distance of the rotation plane swing. Or at least, that’s the case for points that are the same distance from the centre of gravity. The distance of the swing was estimated at 2-300 metres.

However, the paleo pole for the original body was somewhere further down towards the other brown dot or even slightly beyond it. That’s because the head lobe, rising after shear, moved it up towards the first brown dot and then across to the current blue dot when the rotation plane precessed. When the head was on the body, the centre of gravity had to be lower. Therefore the z-axis of rotation had to be lower. Therefore the point at which the z-axis emerged at the surface had to be lower. And the point at which it emerged is the paleo north pole for the single body paleo comet. The lower brown dot is a crude estimate of its location but it had to be straight down the site A rim because that’s in the same plane that the rotation axis rose as the head lobe rose.

PHOTO CREDITS:

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

To view a copy of this licence please visit:

http://creativecommons.org/licenses/by-sa/3.0/igo/

All dotted annotations by Scute1133.

67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 36

COVE PHOTOS AND EXACT ORIGINAL HOLE LOCATION

 
INTRODUCTION

Among other things, this post slowly stumbles towards the original location of the delaminated sink holes, somewhere inside the left hand side of the bottom scallop. That’s pretty close anyway (to within around 100 metres) but the location became more crystallised even while writing. At the end, I suddenly realised where the exact location was. Instead of tidying it up, I’ve left it as is. So there are some very small errors in the body of the text regarding this issue and those are corrected in the last section that identifies the exact original hole location. Leaving in the slightly erroneous path taken sheds light on the reasoning to arrive at the correct location. 

BACKGROUND

The cove on the head lobe with the three scallops and holes is a bit of a chameleon. It appears to change shape and character when viewed from different angles and under different lighting. The bottom scallop was partially nailed down in Part 35 but we could do with some more views of that scallop and the other two above it. So before we carry on with a more in-depth analysis in future parts, it would be as well to post a few more photos from different angles so we can see what the cove actually looks like.

In different photos, the scallops and holes seem to move or disappear altogether. This is entirely due to the viewing angle and lighting. They remain in the same places all the time. There are four annotated photos below, which view the cove from different angles. There’s also a fifth and sixth further on down, both of which are the Part 35 header photo reproduced with different annotations.

In the photos, the four yellow lines denote the ribs between the scallops including the top of the top scallop and the bottom of the bottom scallop, which is the head lobe rim. The four lines enclose the three scallops. The three light blue dots are the three holes that delaminated from one hole on the body. That bottom hole was probably more like a fissure, pressed against the body before the head sheared (see Part 35). 

As stated in Part 34, all three scallops and holes were concertinaed down on top of each other when the head lobe was still attached to the body. This will be elaborated on in Part 37. There’s more analysis of these four photos further on down. It might be worth glancing at them, reading on and then going back to them. Each one is presented along with its unannotated version.

It’s probably best to look at the dotted lines and holes and then cross-reference to the unannotated versions so that you can start to identify the subtle features that delineate the ribs and hole locations. That includes ridges, dips and lines that are next to them, acting as nearby markers. That makes it easier to pin them down in other photos.

Photo 2   
Photo 3

   
Photo 4

   
Photo 5 

   
Photo 5 key:

Three larger light blue dots- the three delaminated holes.

Small light blue- the apparent perimeter of the bottom scallop hole, which is a rather flatter hole. This is more like simple scouring at the bottom of the hole and the ‘perimeter’ is really the line swept by the upper set of gull wings that delaminated from the lower set. There’s a longer, narrative key for photo 5 further below that explains this in more detail. 

The top rib of the top scallop probably extends further round on either side because there are two obvious ridges, one either side of it. However, any possible extensions haven’t been annotated because they only vaguely match the curve below them whereas the central portion matches better. When you look at all three scallops you can see that the top rim did somehow seat down on the one below because it’s the same length and roughly the same height above the next rim or rib down as all the others are from each other. There are probably yet to be identified mini matches along those two flanking ridges at the top. This top rib was also on the cusp of other cross-cutting movements that smudge the curved signature anyway. Those movements will get an airing in a future post. 

The view from below in photo 5 seems to show the top hole as being too close to the middle one and also shows what looks to be the ‘correct’ top hole nestled under the ridge, further up. However, the one under the ridge isn’t a hole but a shadow. If you trace all the spidery lines leading from the actual top hole, they are replicated in the other photos where it’s obvious as the top hole of the three. This apparent anomaly is due to the undulations of the ridden-up or delaminated layers being exaggerated by foreshortening. That makes the top hole look as if it’s much lower down and almost kissing the middle hole. 

There is an isolated fourth hole somewhat further over to the left too. That’s not part of the scallop delamination but it’s almost certainly the result of a horizontal delamination along the shear line. This horizontal delamination will be dealt with soon. So this fourth hole may have delaminated horizontally (then up one layer) from the same fissure as the main three. Or even from the horseshoe crater just next to the fissure. 

The OSIRIS papers have the fourth hole as being one of three obviously round holes, the other two being our middle and upper scallop holes. That leaves the bottom scallop hole, which is admittedly more of a scouring and ripping apart at the bottom of the original hole. That’s not been identified as a hole by OSIRIS for understandable reasons. But it was at the bottom of our delaminated hole and that’s why we are calling it the bottom member of the three holes as well as being their original location. 

The left hand extent of the bottom yellow line appears to protrude out further than the other three. That suggests that the second rib (the bottom rib of the second scallop) sat down onto the first one with its end a little way in from the end of the first one. That is indeed the case. This is more of an annotation choice than a physical anomaly: the bottom rim includes both its scallop and its scoured-out hole base (which is rather whited out hence being dotted around its perimeter). But the upper scallops are annotated separately from their holes. That’s because the two upper holes are very distinct as holes sitting right next to their slightly shorter scallops. However the hole-plus-scallop length of the two upper formations is about the same as the bottom one. 

The confounding issue that puts the bottom hole inside the bottom scallop and upper holes outside their scallops is the delaminated gull wings. Those run from the bottom yellow curve tip on the bottom rim, up at 45° to the middle hole next to the second curve or rib. This is the third set of gull wings that delaminated upwards from the two sets below it. One of those two lower sets was on the head rim, the other, on the body. The head rim gull wing set corresponds to the first five yellow dots of the bottom line but there’s also a curved extension from that fifth yellow dot to the fifth small blue dot up from the bottom. That curve is whited out here (it’s very clear in photo 6, below). The classic gull wing set on the head rim is dotted in small green as well as yellow. That set fits to the body without the curved extension and to the third gull wing set above, with the extension. You can see the dip in the middle, making them gull-shaped. The 45° set is also dotted green and they originally sat sandwiched to the rim set, including the curved extension. That means the top green dot of the ’45° slope’ used to sit on the fifth small blue dot (see the narrative key for photo 5 for a close up of this exact spot and the visible curve extension running up to it). This in turn means that if you reverse the stretch, the second yellow line tags along with the top green dot and also ends up a fair way inside the curve of the bottom yellow line. That makes the middle blue-dotted hole sit directly over the bottom hole and inside the bottom yellow curve as we’d expect. That also means that yes, the end of the second rib curve would indeed stop short of the bottom rim/rib curve end if reseated.

Of course, the scallops got stretched about a bit as they herniated away from the body (remember this has to have occurred before head lobe shear and full-blown stretching of the neck). You can see a small tendency for the scallops and holes to be directed towards the comet’s long extremity as well as upwards from the body. That means the top scallop and hole are slightly biased towards the Hatmehit/Bastet border, which is at the long axis extremity. That induces a slight curve to the left along the cove length. 

NARRATIVE KEY TO PHOTO 5

This is the longer version, explaining aspects of that photo in more detail. 

The bottom blue hole has its perimeter dotted light blue because it’s whited out here. That’s because it’s squarer and shallower. It was formed by the third set of gull wings delaminating from the second set and rising above the second set during head lobe herniation. The second set of gull wings is on the head rim and matches to the first set on the body below them at the shear line (Part 5). The second and third sets delaminated due to the tensile force of stretch. Then, after head shear, they both remained on the head lobe side of the shear line while the first set remained on the body with two slurry piles oozing out from under them. The slurry piles are what shaped the set of three into gull wings. The top, third pair no longer look gull wing-shaped due to stretching upwards but they do preserve a small kink at the requisite middle point. That point is the same distance along from the left hand wing tip as the deeper kink in the second set, which is the rim set. 

The header photo in Part 35 shows a very good close up view of the delamination of the two sets of gull wings on the head and also the outgassing dyke that probably contributed to the weakening between these two layers. Here’s the header for Part 35, reproduced to illustrate this. The key for photo 5 continues after that but with heavy reliance on the Part 35 header as well. 

Photo 6- Part 35 header reproduced. Green is the delaminated gull wings, pale orange is a slid lump, mauve is four gas dykes (more on these dykes in Part 8). Orange is a mini delamination, dealt with below.     
Photo 5 (and 6) key continued: The area swept by the sliding up of the upper set of gull wings is characterised by scouring and that scouring is right next to the trumpet-shaped dyke outlet (left hand mauve line in photo 6). The fact that the dyke is trumpet-shaped at its end suggests the gases were emerging from a fairly thin dyke (which was also part of the thin fissure at the shear line) and expanding under the reduced pressure when they reached the crevice between the gull wings. Then the gases scoured their way between the two sets of gull wings as they were starting to delaminate, thereby loosening them further. So this bottom ‘hole’ of the delaminated three is really just the very bottom of the original hole. As such, it has no depth, just scouring, and the two holes in the upper two scallops formed the depth of the single original hole when they were seated, one above the other, on this spot. This flat, scoured area is more in keeping with the theory that it was pressed hard up against the body or at least, that the trumpet-shaped dyke directly feeding it was pressed hard against the body. There’s some corroboration of this on the body. Seeing as the dyke appears to have been sliced longitudinally, one might expect a mirror image of the trumpet to be found tight against the gull wings on the body. There is a suggestion of such a shape there but it’s a double-curve. If the rest of the sliced dyke exists on the body, it’s under a bed of dust. And the dust-cover discrepancy between any head and body dyke matches is due to the gravity vector being directed straight down the Hathor cliff towards Hapi. That’s why Hapi is full of dust and Hathor completely free of it, except on ‘horizontal’ ledges. So the Hathor dykes, or longitudinally sliced dykes, are as clear as day whereas their purported matches are invisible under the Hapi dust. A final comment on dykes and their uncannily neat longitudinal slicing- they probably got sliced longitudinally in the head shear precisely because they themselves caused the weakening along that exact plane. It would be like drilling adjacent holes along one plane through a block of wood. If you then pulled the two sides of the block it would tend to shear along the weakened plane of the drill holes. The two halves would sport parallel, longitudinally sliced drill holes as straight, shallow trenches- just like those on Hathor.

In photo 5 there’s an extra orange shape. This denotes a mini delamination that would have been sandwiched between the second rib (bottom of the middle scallop) and the lowest rib which is the lowest yellow line on the head rim, with the sharp turns on its right side. You can see how either side of the orange shape matches to the yellow curves: above it to the left and below it to the right. When everything was sandwiched together at the head rim, these three sections sat side-by-side more than being sandwiched on top of each other. That’s because they are laterally displaced as well as vertically displaced. This explains why the rim curve seems much longer and more convoluted on that right hand side. Once seated, the second curve or rib is slightly ‘pushed’ over to the left by the delaminated orange shape. So the second curve starts further to the left than the bottom one, explaining the length discrepancy. 

There are small chronological issues regarding the first and second yellow lines or ribs. The Part 35 header suggests the second rib (bottom of the middle scallop) was closed up, and possibly closed over rock C when rock C was sitting in the horseshoe. Perhaps it widened to the width of the horseshoe in sympathy with rock C’s slide-back and then rose. We now know the second curve was fully closed up at some point and yet today it mirrors the bottom curve faithfully on that side. There has to be a reason for that and the above widening-then-rising scenario is a tentative stab at the mechanism. 

That very straight section on the bottom yellow curve, just after the sharp turn, is the section that was matched to the similarly straight ‘hollow block wall’ in Part 18. The hollow block wall is the straight ridge sloping up the right hand side of the horseshoe crater on the body.

THE EXACT ORIGINAL LOCATION OF THE SECOND HOLE FOUND.

Photo 7- the original location of the second hole (and presumably the third hole on top of it). This is really the scoured base or bottom hole of the three delaminated holes.  
Light blue- the second hole (upper left) and its original seating at the site of the first ‘hole’ which is really just a scoured base.

Green- the upper line is the current position of the delaminated gull wings. The lower line is the location they would have been at while still attached to the head rim set of gull wings but just after delaminating from their seating on the curved extension. That allowed passage of gases from the dyke, through the fluted end of the dyke and between the two delaminating gull wing layers. 

Mauve- path of gases from the dyke, through its fluted exit, between the separating gull wing layers and ending in the middle of the hole base.

Pale orange- the lump that slid with the hole (upper left) as well as its recessed former seating next to the scoured hole base.
 

So the hole wasn’t exactly on top of the gull wing delamination but just above it. Above, it was stated as being sited on the area within the blue-dotted line which was the entire area left behind by the gull wing delamination. But it was sited just above that area because it was formed by gases escaping from between the gull wing layers before they’d actually separated. It looks as if the gases from the interior found their way out of the fluted dyke and between the two gull wing layers even as they started delaminating. The gases then travelled between the two gull wing sets and escaped at their open ends. On emerging from the tight channel between the two sets, the gases probably underwent sudden decompression and were able to push their way up to the surface, thus creating a single ‘sink’ hole. That hole then slid to the upper blue location under the tensile force of stretch. When it arrived at this second location, it then delaminated a second time, allowing the third hole to slide up with its third scallop. 

This means the first ‘hole’ in the bottom scallop was really just the scoured bottom surface of the hole, which then slid away in its entirety. That’s why there’s no actual hole there today but there is this scoured base signature at the end of the gull wings. The area under the gull wing delamination is also scoured but that was the feeder and not the exact location of the hole. That extra area of scouring was why it was misidentified as the actual hole base, above in this post.

PHOTO CREDITS:

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

To view a copy of this licence please visit:

http://creativecommons.org/licenses/by-sa/3.0/igo/

All dotted annotations by Scute1133.

67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 35

HOW THE COVE OPENED UP 
  
   
This post continues on from Parts 33 and 34.

Dark green- the top line used to be sandwiched to the bottom line. The bottom green line, up to the mauve line, is in fact the head rim gull wing match. It matches to the body gull wings 1000 metres below. The upper green line was a third delaminated layer, another gull wing when all three were sandwiched on the body. If you zoom into the unannotated version, you can see a kink along this upper line that’s exactly the same distance along it as the main kink is along the classic gull wings below it. But it’s fairly obvious the two lines match anyway. 

Pale orange- this lump at the end of the upper green line sat in the same shaped trough at the end of the lower green line. The base of the lump is the same distance below its green line as the base of the trough is below its green line. 

Light blue- these are the bottom and middle matching holes that correspond to the bottom and middle scallops. The scallops delaminated along with their holes and rode up when the head began to herniate from the body under the tensile force of spin-up. The bottom hole is shallower, in fact rather flat, betraying the fact that it was an aperture, squeezed against the wider crater rim on the body (as discussed in Part 34).

Yellow- the bottom of the bottom scallop (at the head rim) and the bottom of the middle scallop. These two lines aren’t very useful here but will be when referring back from the next part. They don’t look as if they fit together but that’s because a) the green line is usually marked yellow but is marked green here for matching purposes b) the dark orange feature is a mini-delamination that slid up, away from its original seating on the right hand section of the bottom yellow line. Part of the orange shape is obscured by the yellow head rim that’s slightly nearer to us. When the orange shape is slid back to its seating on the rim, it means the upper yellow curve fits to the left hand section of the orange line and not the lower yellow rim line to the right of that. 

Dark orange- see ‘yellow’, above.

Mauve- dykes as described in Part 8, January 2015. The left line stops short of its opening in order to show its fluted end point that is one of the main gas outlets for the three delaminated holes. If you recall, Part 34 stated that the gull wings slid from the horseshoe crater rim when on the body and opened up an aperture in the process. This is the dyke that fed that aperture. It’s no coincidence that the left side fluting of this dyke kisses the right tip of the gull wings because the gull wing tips defined the slide. The body gull wings still have that slide signature. The other three mauve dykes emerge in the tighter section of cove that corresponds to the small, horseshoe crater 1000 metres below. Since this section of the cove sat against the now open end of the horseshoe it means that it’s the section that rock C was originally shunted against (see Part 33). Rock C has three mini-scallops and its seating in the horseshoe has three corresponding feeders (two mini-scallops, one flat, suspected dyke). That seems almost too neat but there are three dykes here and a hint of three mini-scallops within the cove itself. Mini-scallops seem to be found wherever catastrophic outgassing is suspected to have occurred (because slurry signatures and scouring signatures are also present).  

PHOTO CREDITS:

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

To view a copy of this licence please visit:

http://creativecommons.org/licenses/by-sa/3.0/igo/

All dotted annotations by Scute1133.

67P/Churyumov-Gerasimenko. A Single Body That’s Been Stretched- Part 34

THE COVE DELAMINATED INTO THREE SCALLOPED SECTIONS 
 
Key:

Red- the three scallops that form the so-called cove in the centre of the head lobe, directly above the north pole in Hapi. The cove was first mentioned in Part 3. This is a blurred photo but it shows the three scallops quite well. In most photos, the top one is less obvious due to being shallower and more prone to partial whiting out. And in some other photos there can be a perspective issue, making the bottom scallop appear to merge with the second. 

Light blue- three holes that have delaminated along with the three scallops. 

Photo 2- ESA regions map for orientation in this post. 

 
All references to up, down, left and right are from the ‘upright duck’ viewpoint unless specifically stated. The upright duck viewpoint is with the head lobe of the duck shape sitting directly above the body lobe. 

Some keys to the photos are narrative and quite long so their conclusion is denoted with ‘/////’.

THE COVE AND HORSESHOE CRATER FORMATION

Photo 3- the cove and horseshoe crater formation. 

  
   
Key:

(Checking the unannotated photos will be useful here due to dots obscuring features). 

Upper red arrow- the direction of delamination for the three scallops in the cove. 

Lower red arrow- the direction of the monolithic slide that opened up the horseshoe-shaped crater (Part 33). The horseshoe opening is the flat rim towards Hapi, not the other way round. In other words, it shouldn’t be confused with the yellow-dotted horseshoe of the cove, which is facing the other way. Indeed, the two opposite facing horseshoes, overlapping along their sides are what made this half-crater into a whole crater when the head was seated on the body. Both red arrows point in exactly opposite directions and away from the north pole of rotation situated between them (dark blue dot). They are therefore betraying the radial, tensile forces of comet spin-up. The degree to which the arrows appear not to be in exact opposite directions is due to the head lobe tip-up at the right. When the head was seated, they were in exactly opposite radial directions.

Pale green- the cove perimeter. The three scallops within it haven’t been annotated due to the reasons cited above. However, the arrow tip is pointing to a quasi-rectangular section that is a rib dividing the middle scallop from the top one. The bottom of the arrow is sitting on the rib between the first and second scallops. 

Light blue- three sink holes that delaminated from one sink hole. They delaminated along with the three scallops in the cove. They serve as a guide as to where the scallops are when they’re whited out or in shadow. 

Dark blue dot- (single dot in Hapi). This is the north pole of rotation. It’s where the z-axis of rotation emerges at the comet’s surface. The z-axis is the axle around which the comet rotates. If the axis were produced further out, you could imagine holding it and spinning the comet round on it, as if on a skewer or a spit. If produced out into space beyond the comet surface, the axis would come towards us but pass slightly below us and somewhat to the left. This means the rotation of the comet in this view is downwards at top left and upwards at bottom right. 

Terracotta- the rest of the shear line that’s visible in this photo. 

Small green dots- rock C (on Site A) and its seating (against the back rim of the horseshoe crater). Rock C was introduced and matched to the seating in Part 15. In Part 33 it was shown to have been part of the monolithic slide and to have been attached to the gull wings (Part 5) before the slide. 

Fuchsia- these two dots mark the tips of twin shapes that have delaminated from each other under the tensile forces of stretch, i.e. centrifugal force. They’re essentially triangular but with kinks that make them look a bit like an upside-down India shape. If you draw a line between them and produce it, it skims right past the north pole blue dot. This again betrays the direction of the delamination slide to be radial, away from the north pole. That’s why they are said to have delaminated under centrifugal force. The distance of the slide is the same length as the diameters of the three sink holes on the head. They sat on top of this small section of the shear line (already matched in Part 3). Evidently, the slide of the India shapes opened a new fissure or a newly widened section of the shear line. Gases spewed out and through the layers draped above. That created one hole which then delaminated into the three we see on the head. 

Single yellow dot- this denotes the small horseshoe crater and is in its centre.

Single orange dot- this flat, white area is an upper-level crater that the cove-end slid across in sympathy with the same force vector that delaminated the India shapes (but also with a tug towards Ash due to the radial nature of the vectors). In fact, the cove slide actually created this upper level, with the Babi onion layer sliding back en masse to accommodate the opening. 

Yellow- on the head lobe. This is the cove seating that sat on the horseshoe crater below. 

Yellow- on the body. This is the seating of the original cove position directly before the monolithic slide. It was bent tight around the horseshoe crater with the gull wings attached to rock C when rock C was inside the crater (Part 33). The cove then tore from the left rim, slid to the left, and formed the larger crater. It probably happened at exactly the same time as the monolithic slide i.e. from the moment the gull wings sheared from rock C. Indeed, there’s a gull wing seating remnant that was kicked down and away and left marooned as if not knowing whether to follow rock C or the gull wings. That’s a signature of the two slides happening together and also a subtle sign of a radial force vector radiating from the pole and between the two main slide vectors. 

Light yellow- this is the line to which the cove slid and stretched to. It defines the final seating of the cove before head lobe lift off and is the line that has always been depicted in previous posts for the cove seating. The gull wings correspond to the last four dots. The fourth from the end is attached to the centre of the India shape. The centre of the other India shape is on the horseshoe crater rim. The gull wings slid with the India shapes and that’s why they were said to be attached to rock C at the rim of the horseshoe (Part 33). The gull wing shape of rock C confirmed this. 

/////

This post is concerned with the tearing open of the cove and horseshoe crater formation which then divided into the cove on the head lobe and the crater on the body lobe. The dividing of the two was due to the shearing of the head away from the body. The cove ended up on one side of the shear line, remaining with the head. The crater, which the cove had surrounded like a rim around one side, remained on the body. When seated, the cove surrounding one side of the crater, formed a hole. That hole then became the horseshoe-shaped crater we see today after the cove tore away from it. It’s horseshoe-shaped because the cove used to clamp across one end of it. The cove used to wrap round the sides too but only from halfway up. That’s why, when viewed from above, the crater looks intact on three sides with one open end. That is the case up to a point but the the upper sides were torn away somewhat too by the curving-round cove. The only part of the crater to escape the cove-ripping was the back rim, towards Ash. The back rim performed a monolithic slide-back from that straight front lip of the crater to its current position (Part 33). It slid across the crater floor en masse, with the two side walls acting like rails. It was a very neat rift. 

The tearing open of the crater/cove formation was via tensile force vectors (stretch vectors) acting in a radial pattern surrounding the cove and crater before the head lobe sheared away. These radial forces were centred on or near the north pole, which is the north pole of rotation for the comet. In other words, the north pole is where the imaginary rotation axle pierces 67P. So these radial tensile forces appear to be centrifugal forces brought about by spin-up of the comet.

Whilst there are references in this part to the fact that the cove fits to the body, the matches were already dealt with in detail in Parts 1,3,4,5,6,8 and 18. So we’re not trying to prove the cove fitted to the crater. We’re describing how the cove/crater combination was ripped open and the cove delaminated into three large scallops. It’s true there are references to the matches (and even some refining of them) but that’s incidental to the thrust of the post, which is the ripping apart, the delamination and the radial forces that were responsible. 

THE COVE-WIDENING AND DELAMINATION

The lateral cove-widening event (that created the upper, shallower crater) happened when the head was still attached to the body and most probably occurred at the same time as the monolithic slide. The vertical delamination of the cove into three scallops also happened when the head was seated and would presumably have occurred straight after the cove slide. The monolithic slide (rock C plus seating sliding back to open up the horseshoe crater) would have exposed the weakened, gas-scoured cove layers at one end. That exposed end would have been the part of the head lobe against which rock C and its seating (the monolith) had been attached before the monolithic slide. Except, it probably wasn’t attached by this time because that line is the shear line and we know from Part 33 that gases and slurry were scouring their way up through this fissure. But the monolith would have been against the head with the fissure of the shear line between them. 

The tensile force vector that delaminated the cove was in the exact opposite radial direction to the monolithic slide direction. The north pole is situated almost between the two so the forces that were responsible for the cove delamination were directed away from the north pole and complement the radial force pattern being built up in Parts 32 and 33. This again strongly implicates centrifugal forces. Those forces would have been increasing steadily during comet spin-up due to asymmetrical outgassing. It appears that the cove succumbed to these forces near the time of head lobe shearing. It had to be before head shear because the moment the head lifted off the body, all stretch (centrifugal) forces were transferred to the incipient neck and were no longer available for delaminating the crust. 

The rotation period at the point of head lobe shear had to be around two hours for the missing slabs to have escaped at the required escape velocity speed of 0.8 metres per second. That in turn means a tangential speed of 0.8 metres per second for the discarded slabs. So the delamination of the cove probably started at a juncture just before the two-hour rotation period was reached and continued right up to the very moment the head fully sheared. 

However, the centrifugal forces close to the north pole, due to spin up, would be small due to the small radius of rotation, despite the fast, two-hour period. A small radius gives a slower tangential speed than a large radius at the same rotation rate. The large radius experiences a greater centrifugal force due to the faster tangential speed. That’s why adventurous children hang off the outer circumference of playground merry-go-rounds while cautious ones remain crouched in the middle, next to the axis of rotation. That suggests the delaminating cove and sliding monolith weren’t under enough centrifugal force to display such clear radial stretch vectors. This paradox is addressed below.

THE PIE-SHAPED CRUST EFFECT

The centrifugal forces close to the pole, or rotation axis, are small but the crustal features at the pole such as the delaminating cove and sliding monolith were attached to other parts of the crust at greater radii and under greater centrifugal force. Let’s imagine an idealised cometary crust model essentially made up of pie-shaped sections centred on the pole. Each pie shape would have its small, low-mass (and slow tangential speed) tip kissing the pole and its large-mass (and fast tangential speed) outer section far from the pole. Therefore, the pie tips (represented by the cove delamination and monolith sliding out of the horseshoe) were being yanked back from the pole by sections that were being pulled harder. And those sections were pulling harder because they were under far more centrifugal force due to their greater radius and mass. 

So today’s cove and monolith slide-back are really just betraying the much greater radial forces further out that were pulling on them. The cove and monolith were attached to the crustal matter subject to those greater forces so they both slid as if under a greater force than their radius would suggest. In the merry-go-round analogy, it’s as if the child on the circumference let go of the hand rail keeping him on and grabbed the child in the centre. The child in the centre probably wouldn’t delaminate but he would certainly slide, despite being under little direct centrifugal force. 

The sliding and delamination directions of cove and monolith therefore remain as strong tensile force direction signatures. Those directions are both radial and in opposite directions from where they kissed at the pole. So their current tensile force signatures preserve the radial nature of the centrifugal forces acting on them via their ‘pie-shaped’ hangers-on. And in reality, the hangers-on would be anything but pie-shaped but they would be bigger, more massive and at a greater radius, which is all that’s needed. 

CONCLUSION

This part adds several tensile force vectors to those presented in Parts 32 and 33. They’re all radiating from the north pole, building up the overall radial pattern that implicates centrifugal force via spin-up as the culprit.

There will be more on the cove and horseshoe crater in due course. They are important features with far-reaching ramifications. These will be presented eventually but this post presents the most salient aspects of the cove/crater opening and the cove delamination into three scallops. 

PHOTO CREDITS:

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

To view a copy of this licence please visit:

http://creativecommons.org/licenses/by-sa/3.0/igo/

All dotted annotations by Scute1133.