http://starwars.wikia.com/wiki/Hyperspace/Legends#Hazards
>Hyperspace collisions, whether they be intentional or by accident, could devastate or even destroy a planet. Considering the fact that the output of the reactors of many Capital ships rivaled or eclipsed that of a star, and that the energies needed to make hyperspace travel possible were vast, one could unleash a great deal of destructive power on a target. Even if a planet had its planetary shielding up at the time of a hyperspace collision, it could still have the potential to kill millions on a world such as Coruscant just due to the fallout.[4] One of the more famous hyperspace accidents occurred during the Clone Wars, when the battlecruiser Quaestor collided with the Separatist planet Pammant, fracturing it to its core.[5]