Did you know that comets occasionally split into several co-moving fragments?
Comet Shoemaker-Levy 9 broken in dozens of fragments (click to view)

Comets are only weakly held together, like fluffy uncompacted snowballs. Small stresses, such as those due to heating during close passages to the Sun or from the tidal perturbation of a nearby planet, are often enough to break them apart. The most famous example of a shattered comet was Shoemaker-Levy 9 which split into twenty-odd fragments after a close approach to Jupiter in 1992. The fragments all inherit the speed of the parent comet and therefore move in unison like a flock of migrating geese.

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