Why did the nuclei of the original Shoemaker-Levy 9 comet break into many pieces?

The nuclei of the original Shoemaker-Levy 9 comet break into many pieces as a result of a close approach to the planet Jupiter. During this close approach, the uneven gravitational attractions of the Jupiter on the Shoemaker-Levy 9 comet’s far and near edges broke the fragile nuclei apart.