A rubber duck-shaped comet was formed after a collision between two objects, scientists say.
Comet 67P/Churyumov–Gerasimenko's distinctive shape is made up of a larger and smaller lobe separated by a thick 'neck' region.
The discovery is documented in the latest edition of Nature this week.
Scientists had been previously unclear as to whether 67P was the result of erosion on one comet or whether they were once two separate objects.
Dr Matteo Massironi from the University of Padova in Italy, used high resolution data from the OSIRIS imaging system on the Rosetta spacecraft to study the comet.
He and his colleagues found it was made up of stratified "online-like" layers.
Geological sections through the comet show the larger portion is made up of strata up to 650m thick which are different to the ones in the smaller lobe.
Dr Massironi says the findings, in conjunction with gravity vector data, 67P's shape came about as a result of a low-velocity impact which fused the two comets.
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