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1st in a Series of 4 posts by Talkshop contributor ‘scute’ examines Comet 67P and find it to b a stretched body rather than a contact binary. Navigate to the other 3 parts via the homepage.
Below are two photos of comet 67P/Churyumov- Gerasimenko. The first is a close-up of the so called body, the second is a portion of the head. These two areas have numerous matching points showing that they were once joined together. It therefore follows that 67P/C-G was once a single body that has since been stretched, resulting in the two lobes we see today.
67P/C-G is therefore not a contact binary as has been suggested. Nor is it an unstretched single body that has been eroded to form the separate head and body.
As it’s clear the comet was stretched, it must have been subjected to one of two scenarios. It either underwent a close approach to Jupiter under the Roche limit in the distant past or it underwent spin-up to around a 90-120 minute rotation period which would overcome its gravitational pull. The former scenario would need to allow stretching…
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‘It either underwent a close approach to Jupiter under the Roche limit in the distant past or it underwent spin-up to around a 90-120 minute rotation period which would overcome its gravitational pull.’
We know it had at least one close approach to Jupiter, but it was quite recent.
‘Before 1959, Churyumov–Gerasimenko’s perihelion distance was about 2.7 AU (400,000,000 km). In February 1959, a close encounter with Jupiter moved its perihelion inward to about 1.3 AU (190,000,000 km), where it remains today.’
http://en.wikipedia.org/wiki/67P/Churyumov%E2%80%93Gerasimenko
Its spin rate changed slightly and is now in a ratio of 4:5 with Jupiter.
Or it was once molten.
I asked at his blog if the analysis holds if the comet is mostly rock and/or other hard minerals.
Etched, not stretched.
By my reckoning, 20+ points of “match” is roughly a 1 in 2^20 chance that the two lobes were *not* touching in the past along those 20+ points. Stretched is a certainty. “Etched” is unlikely because etching would have randomly modified the matching points.
NeilM asks perhaps once it was molten, bodies of this shape are created easily by huge electric arcs, smaller bodies of the same shape can be created easily using arcs with our piddly electric supply.
The science being used here is forensic photogrammetry.http://www.hgexperts.com/article.asp?id=5220 . It has nothing to do with cometary science per se. It is about matching a relationship between points on the head and points on the body. A 3D model can be surmised and measurements made.