Comet 67P's Double Lobed Shape Formed When Two Comets Collided

Scientists say the double-lobed comet 67P got its shape when two independently formed comets collided. The shape - which has been described as being rubber ducky shaped - arose from a low-speed collision between two comets. The shape was not caused by localized erosion.

Matteo Massironi, lead author from the University of Padova and associate scientist of the OSIRIS team, says in a statement, "It is clear from the images that both lobes have an outer envelope of material organised in distinct layers, and we think these extend for several hundred metres below the surface. You can imagine the layering a bit like an onion, except in this case we are considering two separate onions of differing size that have grown independently before fusing together."

Matteo and his team identified and studied over 100 terraces on the surface of the comet. They also studied layers of material visible in exposed cliff walls and pits. A 3D shape model was built to examine the direction the terraces are sloping. The researchers say it quickly became clear that the features were coherently oriented all around the comet's lobes.

Matteo says, "This was the first clue that the two lobes are independent, reinforced by the observation that the layers are inclined in opposite directions close to the comet's neck. To be sure, we also looked at the relationship between the local gravity and the orientations of the individual features all around the reconstructed comet surface."

The research paper was published in the journal Nature. A diagram here explains the researchers' findings. A Slate article ("How to make a rubber ducky comet") about a previous study contains an animation showing how a slow-speed collisions between two objects could result in the double-lobe shape seen in Comet 67P.

Image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; M. Massironi et al (2015)

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