Comets' Nuclei Break Up And Make Up Over Their Life Time

Comet 67P/Churyumov-Gerasimenko. ESA

Just like those annoying couples that are constantly on the “it’s complicated” setting, cometary nuclei tend to have a troublesome history.

According to a new study published in Nature, some of the comets that orbit the Sun in less than 200 years regularly split in two and merge back together. The team showed that if comets suddenly begin to spin more quickly, the strain created can form cracks on the surface. 

The team, led by Purdue postdoctoral fellow Masatoshi Hirabayashi and CU-Boulder Professor Daniel Scheeres, believe that this model can explain the formation of several "bilobed" comets like 67P/Churyumov-Gerasimenko (67P).

67P has a characteristic rubber duck shape that has fascinated the public and experts alike. However, it is not alone: Of the seven comet nuclei that have been imaged at high resolution, five have two large lobes connected by a thin neck. Trying to understand the reason behind it, the team devised a computer simulation of 67P.

As these comets pass near the Sun, they can start outgassing as well as get extra torque by gravity, which changes their spin. This gravitational effect can also be produced when passing near a gas giant. The model shows that 67P should have two large cracks on the neck due to this phenomenon and those have been observed.

“Our spin analysis predicted exactly where these cracks would form,” said Scheeres in a statement. “We now have a new understanding of how some comets may evolve over time.”

67P must have been spinning on itself every seven to nine hours to produce the cracks; for now, it is safe from splitting as it rotates every 12 hours. If in the future 67P's rotation reaches the seven-hour benchmark, the comet will break into two chunks. If this happens, 67P’s lobes will split apart and then slowly collide back together, similar to some of its fellow comets.

“The head and body aren’t going to be able to escape from each other,” Scheeres added. “They will begin orbiting each other, and in weeks, days or even hours they will come together again during a slow collision, creating a new comet nucleus configuration.”

If these findings are confirmed, the role comets have played in the early Solar System would be significantly small as they would not have survived for long. It's possible the destruction and reformation of the nucleus could be a periodic occurrence in the life of these comets until they become so eroded that they disappear.

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