SAN FRANCISCO---As scientists continue to pore over new images and data from the Rosetta mission to comet 67P/Churyumov-Gerasimenko, clues are emerging that may help answer a puzzling question: Why is this comet shaped like a duck?
The comet consists of two lobes, which, if you squint, look a bit like the head and body of a duck. The odd shape could have been formed by erosion from jets and bursts of gas shooting out from the comet, blowing off material to carve out the comet’s neck. Or, the head and body might have been two separate pieces that crashed into each other and stuck.
Now, an initial analysis based on new images from the Rosetta spacecraft orbiting comet 67P reveals fractures and layering features that seem to support the latter scenario, says Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colorado. He presented the results on Dec. 18 here at the American Geophysical Union meeting.
Comet 67P’s double-lobed shape isn’t unusual. Both comet Borrelly, which was visited by Deep Space 1 in 2001, and comet Hartley 2, which was studied by NASA’s Deep Impact/EPOXI spacecraft in 2010, have two lobes. But scientists haven’t been able to determine for sure whether the comets were formed from erosion or a collision. Whichever the case, the process seems to be a general one that happens to many comets.
Using new images taken with Rosetta’s OSIRIS camera, Marchi and his colleagues found terrace-like layers on the comet’s body. The layering aligns perfectly with parallel lines seen on the opposite side of the body, suggesting that these layers extend through the body as part of its internal structure. Although the head also has layers, they don’t align with those in the body, which implies that the two lobes were once two separate pieces. If the head and body were made from one piece, the layers should extend through both lobes in the same direction.
The neck of the comet also shows signs of a collision between the head and the body. The region is covered in big fractures, which would have been created by shockwaves that blasted through the comet during a crash. Some of the fractures are also misaligned, suggesting that they belonged to what were separate, smaller chunks that were floating around when the head merged with the body.
The general appearances of the head and neck are also somewhat different, according to the analysis. For example, there are more smooth patches that cover the body than the head.