Comet 67P looks to have been glued together, not sculpted

The comet looked vaguely like a rubber duck, some thought. The findings were published Monday in the journal Nature.

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.

In the year and change since the European Space Agency’s Rosetta mission became the first spacecraft to orbit a comet, the probe has made all sorts of discoveries about the object known as Comet 67P/Churyumov-Gerasimenko-for instance, that it’s bumpy, not smooth as expected, and is covered in dark, carbon-rich compounds with surprisingly little ice. One with the comet as a single body with a center of mass near the ‘neck.’ The other one with two separate comets, with each having its own center of mass.

Lead author Massironi continues, “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”.

Planetary scientist Jay Melosh of Purdue University has studied comets extensively through his participation in NASA’s Deep Impact, NExT, and EPOXI missions, investigating comets Tempel 1 and Hartley 2.

“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.

The other hypothesis is that comet 67P is actually two comets, long ago welded together after a chance meeting.

67P made history back in November 2014 by becoming the first comet to ever be explored by a probe.

The team found that the orientation of a given layer and the direction of the local gravity are closer to perpendicular in the model with two separate objects, rather than with one.

“Our analysis… clearly shows that the layers of the body and the head of the comet are not related”, Massironi said.

Scientists don’t know if comet twins are common, or if 67P is an oddity, but the results may provide an important clue about how comets – and the planets – formed.

The two lobes have similar composition, so the team still believes they were formed from smaller pieces of material in the same region of space.