Comet 67P/C-G was formed by a soft collision

Scientists, using data from Rosetta, have concluded that Comet 67P/C-G’s double lobed shape was caused by the slow-motion collision of two distinct comets.

By using high-resolution images taken between 6 August 2014 and 17 March 2015 to study the layers of material seen all over the nucleus, they have shown that the shape arose from a low-speed collision between two fully fledged, separately formed comets. “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,” says Matteo Massironi, lead author from the University of Padova, Italy, and an associate scientist of the OSIRIS team. “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.”

While erosion continues to eat away at the comet’s surface, changing its shape, the two lobes formed separately, though in much the same way.