When the European Space Agency’s Rosetta spacecraft sent back the first images of Comet 67P/Churyumov–Gerasimenko, scientists were surprised by how much it looked like a rubber ducky. A new analysis finally explains how this comet acquired its distinctive shape.

After Rosetta sent back the first detailed images of the comet back in July 2014, two different theories emerged to explain its strange appearance.

“This is unlike any other comet we have ever seen before,” noted OSIRIS project manager Carsten Güttler in a NASA statement back in July 2014. (Image credit: ESA/Rosetta/MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)

One was that it formed through the merger of two comets, the second suggesting that localized erosion on a single comet produced the “neck” feature.


An unexpected shape. (Image credit: ESA/Rosetta/NAVCAM, CC BY-SA IGO 3.0)

Now, after an analysis of high-resolution images taken between August 6, 2014 and March 17, 2015, scientists from the University of Padova, Italy, have shown that the shape arose from a low-speed collision between two separate comets.


“It is clear from the images that both lobes have an outer envelope of material organized in distinct layers, and we think these extend for several hundred meters below the surface,” noted lead author Matteo Massironi at the ESA’s Rosetta website. “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.”

Massironi’s team identified over 100 terraces on the surface of the comet, along with parallel layers of material located in exposed cliff walls and pits. A 3D model showed the directions in which they were sloping, and how they extended into the subsurface. The features were oriented all around the comet’s lobes, and in some places down to a depth of about 2,130 feet (650 meters).


“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,” says Matteo.

The team’s observations were reinforced by models which computed the strength and direction of the gravity at the location of each layer.


[ ESA ]

Email the author at george@io9.com and follow him at @dvorsky. Images: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; M. Massironi et al (2015)