The Blocky Rectangle


Copyright ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/A.COOPER

The blocky rectangle has a line of green dots along the top rim of its shadowed cliff. A long arrow points along the length of its mesa-top and exactly down its centreline. A blanket-like structure slopes away gently from its front-left side in this view. A shadowed indent halfway along the left perimeter mirrors an indent on the right. This is the resumption of the cliff where there’s no blanket draping from it. Photo culled from Part 50. Please click on Part 50 link at bottom for more information.

This page is for Andrew who left a reply to a comment I made on the Rosetta blog about the so-called “blocky rectangle”. The Rosetta blog post is here:

http://blogs.esa.int/rosetta/2016/11/14/space-science-image-of-the-week-navcam-close-ups/

My comment and Andrew’s reply are the first two below the article. 

This page is a summary of all research done on the blocky rectangle. There are nine parts in which the blocky rectangle features and these parts are listed below. Some other parts refer briefly to the blocky rectangle or the processes that brought about its morphology but this page summarises 95% or more of the blocky rectangle references and probably 100% of its morphological evolution. That is, 100% of what is known so far. 

This page invokes stretch theory which is the stretching of 67P due to the centrifugal force of spin-up. This theory isn’t accepted by the OSIRIS team, by the Rosetta mission nor the scientific mainstream in general. If you’re interested only in peer-reviewed work, this saves you from reading further. 

Before the individual parts, there’s an introduction and an overview of the general discoveries leading to an understanding stretching of the comet before the head sheared. This was written up in the sub-series (Parts 22-29). The blocky rectangle’s morphological evolution is entirely bound up in the narrative laid out in the sub-series. Hence the overview below, rather than just plucking out the parts referring to the blocky rectangle. If that was done, they’d appear not to flow from one to the other due to the lack of an overarching narrative. 

INTRODUCTION

The blocky rectangle is first dealt with in Part 22 but only indirectly. Parts 1 to 21 dealt only with the head-body matches and the consequences of the head breaking away. It was then realised that the single body had stretched greatly prior to head shear and neck stretch. The only stretch before that point was thought to be the neck stretching as the head lobe lifted off. In truth, there was a gradual realisation from about Part 15 but it took time to join the dots. 

Marco Parigi’s onion layers were instrumental to realising there was stretch before shearing. The first south pole picture, in March 2015, showed what seemed to be an impossible strata arrangement on the head because they went the opposite way to those at the north pole side of the head. The only possible interpretation was adopting Marco’s onion layers (which we’d dropped in January, deferring to expert opinion) and have them slide up the head. This led to finding many matches between these sliding layers, as you’d expect. From there, I realised that the sliding layers weren’t simply sliding due to the centrifugal forces but being forced to do so by a stretching core. This led to discovery of the body diamond shape which is aligned with V-shapes on the head. That led to understanding the reason for Serqet’s and Nut’s existence, which in turn led to the four coloured anchors/matches below Serqet. This meant Serqet once sat like a large, upright wall on the body. That allowed me to see the sliding layers on the body for the first time, which led to the discovery of the ‘red triangle’ that was protected from tensile forces of stretch by Serqet when Serqet was on the body. It was in the lee of Serqet. 

The blocky rectangle sits along one side of that triangle and inside the line i.e. within the triangle. The triangle is defined by two identical tensile force lines (stretch induced lines) that joined at Apis at the comet’s long-axis tip and skirted Serqet before running down either side of the proto head lobe to meet again at Aker. These two important lines were the starting point for the sub series, which related all these finds in their logical order which was the exact reverse order to which they were discovered. 

THE SUB-SERIES

Parts 22 to 29 were a sub-series within the whole 69 Parts (so far). The eight parts of the series gradually built up evidence for stretching of the single body before the head sheared from the body. The first part, Part 22, describes the ‘slab A extension’ a particularly ripped up or scalped-looking area on the body lobe. The extension’s southern perimeter is seen to be extremely straight. This line is contiguous with the red triangle side and is therefore one of the tensile force lines. Along with its twin, it’s the key to everything described in the sub-series and also to what’s described below. 

The blocky rectangle’s evolutionary morphology is entirely bound up with this line. It’s a tensile force line and a shear line combined, hence its straightness. It was brought about by the centrifugal force of spin-up and stretch and it’s one component of the pair that each made their way down either side of the proto-head lobe as it herniated from the body just prior to shear. It caused the blocky rectangle’s long vertical cliff on one side, by shearing along it, hence its vertical nature. And it indirectly caused the two slightly less vertical cliffs at either end as well as the ‘blanket’ on the fourth side. 

THE SEPARATE PARTS DESCRIBING THE BLOCKY RECTANGLE

Part 22– especially Photo 2 (3rd to 4th bright green dots). The blocky rectangle isn’t called that yet in this Part. Its morphology isn’t understood but the really significant thing is that the straight, vertical cliff of the rectangle is right on that 1km-long green line and seems defined by its straightness. The conclusion (‘take home message’) dwells on this very straight line as being a clue to head lobe stretch before shear but waits for its twin in Part 23 to be discussed before their significance starts to emerge. (It’s a tensile force line due to spin-up and stretch. That also makes it a shear line between less and more disturbed areas).

Part 23– the twin line creating an isosceles triangle (not so important to read).

Part 24– the four coloured matches. Although the blocky rectangle doesn’t really feature here, it’s already known that it tore from the back side of the mauve match/anchor hence the cliff at that end. The blocky rectangle is intimately related to the mauve anchor and was for all intents and purposes, part of the anchor before it tore away under tensile stress due to centrifugal forces of spin-up. Since it’s related to the mauve match/anchor body component it means it’s related to the mauve head component as well. Just behind the mauve head component is another blocky rectangle of the same length and cross-section. It’s clear that when head was joined to body via the clamped mauve matches, the head blocky rectangle joined end to end with the body blocky rectangle as one long strip of the same cross-sectional dimension. The head’s blocky triangle is usually called a ridge or “bright green ridge” because it’s been related to that straight bright green line on the body since Part 22 (in line with it and directly above). Photo 8, “Focus on the mauve anchor” shows the bright green line extending down into Hapi and the ridge on the head, poised above, to seat itself on that extension if we reversed the stretch. See also Part 70 below. 

Part 26– (see ‘signature 6- “the red triangle recoil”). This is where, for the first time, the blocky rectangle is seen to have slid back by ~200 metres but not in isolation. It’s Part of the recoil line. The recoil line is one of several ‘en echelon’ layers behind it. These have been identified and matched up since just after this post, Part 26. They were promised their own post, but are always at the back of the queue so they’re not blogged to date. 

Part 27– from signature 6 onwards. Some of this would seem irrelevant to the blocky rectangle for any reader at the time but you already know the head ‘bright green ridge’, that’s discussed in this part, matches the blocky rectangle on the body. There are some minor mistakes in this part regarding layers and the ridge being forced round the bend at the end of Serqet: it’s now known that Serqet herniated from the body prematurely and pushed through the layer above that unzipped to accommodate its passage through. This unzipping forced the ridge to the side of the end of Serqet bulging through. So the ridge wasn’t “attached at the two pink dots” at the bottom of Serqet but to a chunk at Nut (see Part 57 for the Serqet push-through). Near the end, it talks of the sloping ‘blanket’ side of the blocky rectangle. It’s not a very good explanation because this area was going to get its own post. But it too is sitting in the queue. 

Parts 48/49– (48 is photos only; click through for 49 which has the explanation as well). This is the 1.6 x 200m rift. This finally explained how the ‘bright green’ tensile force that runs alongside the blocky rectangle cliff caused the demarcation line between the morphologies either side of it. Part 26 had already said that the isosceles triangle (the ‘red triangle’) had been in the lee of the ‘Vertical wall’ (herniating Serqet). This protected the triangle from the longitudinal tensile forces while mayhem reigned outside it i.e. with the “ripped-up” slab A extension of Part 22 on the other side of the green line. 48/49 recognised the 200m wide rift with the very straight green line as its southern perimeter. So the southern perimeter of the rift is contiguous with that straight blocky rectangle cliff- it was ripped along that line by the longitudinal shear forces along the line. You can even see the boulder field generated by this one-off shear. It’s at the foot of the blocky rectangle and exactly the same length. But significantly, the boulder field is staggered along from the cliff line. This is because the cliff obviously carried on sliding back along the rift line after the other side of the rift had torn from it and moved 200m away (I’ve also found the match to the cliff on the other side of the rift.)

Part 50– this focusses exclusively on the blocky rectangle with a good OSIRIS close-up. It brings together the opening rift vector force and the longitudinal shear along the southern rift perimeter (which is the bright green line). Notice they’re exactly 90° to each other because the rift opened up at 90° to its perimeter lines. However this is a pseudo vector. The two sides opened as both slid down the body. The 90° is ‘rift-centric’ to an observer sitting on one of the two perimeters looking at the other one while both slide down the body at slightly different angles (vectors are shown in 48/49 photos and more comprehensively in Part 37). 

Part 70- not published as of this page publication. It’s the next part, out soon. This talks of the ‘dagger-shaped’ formation which has the Hapi extension of the bright green line as its very straight and slender double-blade, the mauve anchor as its crossguard and the blocky rectangle as its hilt. The hilt used to be joined to the crossguard. The shape of the dagger is argued as being a visible manifestion of the tensile forces of stretch as well as the related forces of the opening 200-m rift. The drop-down of the bright green line into Hapi was noted all the way back in Part 24 of the sub-series (22 to 29). In that part, it’s noted that it originally sat *under* the bright green ridge on the head at the end of Serqet i.e. the one that looks just like the blocky rectangle and used to be attached to it. It had to sit on the Hapi line-extension i.e. on top of the dagger blade because the blocky rectangle is itself the hilt of the dagger. The head ridge and blocky rectangle were joined via the mauve match. And dagger blades are attached to their hilts via their crossguards.