Scientists have been puzzled since previous year when a Europe's Rosetta probe landed on the surface of a comet and they got to know about its rubber duck shape. Scientists think either the odd shape was because of localized erosion on Comet 67P/Churyumov-Gerasimenko’s surface or likely the merger of two comets.

On Monday, a study was published in Nature. The study concluded that it was a collision that resulted into the comet's unique, double-lobed look. In November, the European Space Agency's Rosetta probe landed on the comet, and was the first every successful attempt to land on a frozen leftover of the solar system's birth.

Researchers used the high-resolution images captured between August 6, 2014 and March 17, 2015 for studying the layers of material visible across the nucleus, and they showed that the shape was made due to a low-speed collision between 2 fully fledged, separately formed comets.

Holger Sierks, of the Max Planck Institute for Solar System Research in Göttingen and principal investigator with the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) said, “How the comet got its curious shape has been a major question since we first saw it. Now, thanks to this detailed study, we can say with certainty that it is a contact binary”. OSIRIS was the primary imaging system of the Rosetta mission.

For the study, scientists initially used pictures for the identification of more than 100 terraces seen on the comet’s surface, and parallel layers of material clearly seen in exposed cliff walls and pits. Then, they used a 3D shape model to find out the directions in which they were sloping and for visualizing how they extend into the subsurface.

"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," he said.

"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," Matteo said.