This blog was set up in December 2014 with the sole purpose of proving that the Comet 67P/Churyumov-Gerasimenko was once a single body that has since been stretched into two separate lobes. This could have happened via one of two different processes.
The first process is spin-up due to asymmetrical outgassing causing a torque on the comet. For this to happen, the rotation period of the comet would have been between 3.5 and 4.5 hours.
The second process is a ‘Roche pass’ at Jupiter where the comet would have been stretched due to the tidal effects below 135,000 km altitude. A Roche pass is also likely to induce spinning in such a way as to exaggerate the delta g forces of the tidal stretching. This depends on the pre-pass rotation period and axis and the altitude of the pass. If such spin exaggeration occurrs, the pass altitude could be higher than the non-rotating scenario for any given stretching force.
Both processes are well-known and documented in the astronomical literature. Even asteroids can be spun up over millions of years (via YORP effect) to a circa 2-hour rotation period before flying apart. 67P’s period has decreased by 20 minutes since 2009, due to asymmetrical outgassing (Sierks et al, September 2014). That is a blink of an eye on astronomical timescales. Similarly, comets have been observed to shred as they pass under the Roche limits of the Sun and Jupiter. Slightly higher passes will induce stretch without shredding.
Stretch theory has been completely overlooked as a means of explaining the shape of 67P. This is because comets are thought to be too brittle to stretch. This would indeed be the case if they were solid ice. However, it is becoming increasingly apparent that 67P is a loosely held together pile of ice pebbles with 70-80% porosity and a tensile resistance of 10 pascals in the ‘neck’ region between the two lobes (Thomas et al, January 2015). Spin-up at 3.5 to 4.5 hours would easily over come this tensile force and so stretching would occur as a result. The sub-135,000 km Roche pass would also overcome this tensile resistance.
None of the above is actually necessary to prove the stretching of 67P into two separate lobes. The two processes are simply cited as well-known mechanisms for anyone who may object to stretch theory at the outset and won’t therefore be inclined to look at the other evidence.
The evidence for such stretching is abundantly clear in the fact that there are a multitude of matching features between the two lobes along the ‘shear line’ where they separated. These matching features are documented in exhaustive detail in Parts 1-6 of this series. Parts 7-15 then go on to explain the multitude of strange features on 67P, which are baffling the Rosetta mission scientists. They are fully explicable when stretch theory is invoked. Part 16 will return to the matches between head and body and Parts 17 onwards will explain yet more of what we see on the comet as directly or indirectly the result of stretching.