At the European Planetary Science Congress going on these days in Nantes, France, evidence were presented that the strange shape of the nucleus of comet 67P/Churyumov-Gerasimenko is due to the fact that it was born from the merger of two small comets occurred a few billion years ago. The study conducted by a team led by Matteo Massironi, a researcher at the University of Padua and Italian INAF (National Institute of Astrophysics) associate, was published in the journal “Nature”.

Ever since it was discovered, the strange shape of the nucleus of the comet 67P/Churyumov-Gerasimenko, consisting of two lobes, was investigated. There were two possible explanations: two comets merged or a massive erosion had dug very deep into the nucleus of the comet until it assumed its current shape.

The team that carried out this study used high-resolution images taken between August 6, 2014 and March 17, 2015 by ESA’s Rosetta space probe. In this way the researchers studied the layers of material of the nucleus to determine that it’s the result of a low-speed collision between two comets that formed separately.

Matteo Massironi explained that the images show that both lobes of the comet 67P/Churyumov-Gerasimenko have an outer shell of material arranged in distinct layers. He and his colleagues believe that this structure extends below the surface of the comet for several hundred meters. The layering is a bit like that of an onion but in this case there are two different sized onions grown independently which merged later.

These conclusions were reached after having identified and analyzed over a hundred terraces on the surface of the comet 67P/Churyumov-Gerasimenko and parallel layers of material clearly visible along the walls of exposed rock. At INAF-Astronomical Observatory of Padua a 3D computer model was created and then used to determine the inclinations of these layers and figure out how they extend underground.

It soon became clear that these layers were consistently oriented all around both lobes of the comet 67P/Churyumov-Gerasimenko and in some areas extended to approximately 650 meters (about 2,130 feet) deep. This was the first clue, reinforced by the discovery that the rock layers are inclined in opposite directions near the comet’s neck. The impact between the two original comets must have taken place at low speed to maintain the stratification.

To be certain, the researchers also examined the relationship between the local force of gravity and the orientation of the individual layers around the surface of the computer-generated comet. Normally, the layers of material form an angle perpendicular to the direction of the force of gravity acting on an object placed above them. The results showed that the model with two separate objects matched the available data better.

This research confirmed previous studies that pointed out the similarities between the two lobes of the nucleus of comet 67P/Churyumov-Gerasimenko. This means that they formed through similar processes of accretion. The two-lobe nucleus didn’t form due to erosion but this phenomenon has nevertheless an important role in its evolution today.

This discovery provides important information about the origin of the comet 67P/Churyumov-Gerasimenko, which confirms that it’s extremely interesting from the scientific point of view. Its study is providing new data on the evolution of comets and in general on the history of the solar system in a mission that is still going on so it can still tell us a lot.

[ad name=”AmazonDocumentary”]