Two-comet dance gave 67P its duck shape

摘要

The rubber-duck comet formed not with a bang, but a whimper. No one actually knows how comet 67P got its distinctive shape. But everyone's favourite comet chaser, the European Space Agency's Rosetta spacecraft, thinks the comet's birth wasn't nearly as traumatic as it might have been. Hans Rickman of Uppsala University in Sweden and colleagues saw two possibilities. One is that two chunks of ice and dirt, the building blocks of comets, merged at slow speeds early in the solar system's history. Alternatively, the two lobes were part of a single larger body that shattered in a violent collision, only for the two chunks to find each other again and stick together.