Researchers said in a paper, published in Nature, that the nucleus of comet 67P/Churyumov-Gerasimenko was made of two formerly separate bodies that have possibly come together in a gentle collision when the solar system was at forming stage. They said it’s a cometary collaboration that lasted billions of years.

In July 2014, the European Space Agency’s Rosetta orbiter started sending back the earliest pictures of comet 67P’s strange, bi-lobed shape. Since then, scientists have been wondering about the origins of its unusual morphology.

The comet consists of three different regions, including a main lobe (the main body of the ‘duck’), a small lobe (the head) and a thin, neck-like area, connecting the two.

Matt Taylor of the European Space Agency, project scientist for the Rosetta mission, said, “Since we resolved the comet, the question of whether it was two objects that joined together or one comet that has been eaten away has been dangling. Now we have answered it — it’s a contact binary”.

An international study team came to this conclusion after analyzing images of the comet gathered by cameras aboard the Rosetta orbiter.

The key interest of the researchers was in different layers of material known as strata that were seen along many steep cliffs of the comet, continuing to be at least 2,000 feet into the comet’s nucleus. These co-centric strata have suggested that the comet’s structure is alike an onion.

“All together, these three lines of evidence leave a very narrow space for doubt,” said Matteo Massironi of the University of Padua in Italy, who led the investigation.

“If you put it together, it looks like you have two onions sitting next to each other, not a single onion with a piece taken out,” he said.