We finally have an answer to why Rosetta's comet looks like a duck
In a paper published today in the journal Nature, researchers conclude that the two lobes on the double-lobed comet the Rosetta spacecraft has been monitoring (also known as 67P) were once two separate comets. But sometime during the early days of the Solar System, they collided.
67P made history back in November 2014 by becoming the first comet to ever be explored by a probe.
The European Space Agency, which is in charge of the Rosetta spacecraft's mission around 67P, lost contact with the probe in July.
Since then, the comet - still accompanied by Rosetta - has passed its closest point to the sun, a major milestone for the mission. Rosetta's mission has been extended until September 2016, so the ESA has a good long while to figure out more about this mysterious comet.
One of the biggest questions they had was how the comet got its strange shape.
By studying pictures collected by Rosetta from August 2014 (when the spacecraft met up with the comet) and March 2015, scientists looked at the layers of the comet to figure out that it was likely the result of a slow collision that happened sometime during the time of the early Solar System.
Judging by the pictures, they could tell there were different layers on the head of the comet and the body. They found that the layers on the larger lobe of the comet were 650 meters thick in some places, which wasn't the case with the layers on the smaller lobe.
"You can imagine the layering a bit like an onion," the paper's lead author, Matteo Massironi of the University of Padova, Italy said in an ESA blog post. "Except in this case we are considering two separate onions of differing size that have grown independently before fusing together."
The surface of comet 67P is riddled with sinkholes, smooth surfaces, and layers upon layers of rocky terrain that helped Massironi and his team determine how the comet got its shape.
The researchers also cross-referenced this idea of layers with gravity fields, shown below in green, which suggested that the two lobes were at one point independent of one another and still had their own centers of mass:
