Comet 67P cracking under pressure

PASADENA, Calif. — It’s hard being a comet sometimes. Comet 67P/Churyumov-Gerasimenko is developing stress fractures and might break apart in the next several hundred years.

Comet 67P is famous for its oddball shape. With two lobes joined together at a neck, it vaguely resembles an interplanetary peanut. The Rosetta spacecraft, which ended its 26-month visit to the comet in September (SN Online: 9/29/16), noticed a large crack in the neck in 2014. After the comet made its closest approach to the sun in August 2015, the fissure grew by several hundred meters and new cracks appeared.

The fractures appear to be developing as forces subtly bend the comet to and fro, Stubbe Hviid, a planetary scientist at the German Aerospace Center Institute of Planetary Research in Berlin, reported October 17 in a press conference at a meeting of the American Astronomical Society’s Division for Planetary Sciences. Hviid and colleagues combined maps from Rosetta with computer simulations of all the forces at work within the comet to determine how the cracks develop. They found that the two bulbous ends rock in opposite directions as the comet spins, flexing the neck and creating severe stress. Because the comet isn’t held together strongly — it’s a conglomeration of dust and ice not much stickier than snow, Hviid said — the neck is starting to break. After a few hundred more years, he said, the comet could fold itself in half as the two lobes snap apart and smoosh together.