Nova device

The Nova device was a weapon of Movellan design which was capable of destroying an entire planet.

During the Dalek-Movellan War, a Movellan force followed a Dalek group to their homeworld of Skaro where they sought to reawaken Davros in order to use him to program their battle computers to end the logical stalement the Dalek Empire was facing against the Movellans.

When discovering their aim, the Movellans planned to use the Fourth Doctor to reprogram their own battle computers to defeat the Daleks. In order to deny the Daleks a similar advantage, they planned on detonating the nova device on Skaro thus destroying Davros and his creations but this was thwarted by the interference of the Doctor along with his companion. (DW: Destiny of the Daleks)