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According to researchers, Rosetta’s comet got its peculiar rubber-duck shape following a collision between two previously separate solar system bodies.
The study was published in the Nature journal, and offers an explanation for the distinctive shape displayed by the nucleus of comet 67P/Churyumov-Gerasimenko.
The comet has been stirring speculation ever since July 2014, when the European Space Agency’s Rosetta orbiter broadcast the first images of its bi-lobed appearance. Philae landed successfully on the comet on November 12, making this the first time in human history when soft landing on a comet nucleus was achieved.
Comet 67/P has been likened to a rubber duck because it has a minor lobe (the head), a larger lobe (the body of the “duck”) and a narrower section connecting the two (the neck).
Formerly, researchers had been left undecided whether this unusual morphology had resulted from 2 objects joining together, or from a single object being eroded in time.
Now, it has been established that the comet is a “contact binary”, according to Matt Taylor, project scientist for the Rosetta mission. This discovery was made after a thorough analysis of high-resolution photographs taken by cameras aboard the orbiter, between August 6, 2014 and March 17, 2015.
If the comet had been composed of a single body, then its layers of material would have been displayed concentrically, like onion rings, around a point of gravity located near the neck.
However, scientists determined that these distinct strata are actually arranged around 2 separate points of gravity, one for each lobe. Therefore, the two parts had initially been distinct, and each of them had formed around an individual center of mass.
Also, scientists concluded that the thin region connecting the two lobes also formed separately, because its layers of material don’t match those corresponding to the rest of the comet.
Gravity vectors were also assessed by the team of researchers, led by Matteo Massironi of the University of Padua in Italy. Their analysis, based on computer models, showed that layers from lobes have opposite inclinations, giving further proof to the theory that the comet was formed by fusing two separate objects.
However, given the structural similarity between the parts, it appears that they may have originated from the same region of the solar system, or they may have resulted following identical processes.
Researchers believe that the impact of the two mini-comets that merged together was actually relatively gentle, since otherwise the objects would have broken apart. The low-velocity collision, which is estimated to have occurred in the early beginnings of our solar system, displaced some parts of the bodies, leaving the rest intact.
Scientists speculate that the lobes are held together by gravity forces, but also by some “processes of cementation”. Nevertheless, for now they are conducting further tests, before giving a final verdict.
Image Source: ESA
