Detonator it set off an electro magnetic pulse (EMP), which destroys all deployed ships in on the affected body. It can be built at the Shipyard after you build a Munitions Lab. Inhabitted planets have so much eletro-magnetic energy pulsing through the atmosphere already that any detonations would just disipate into the amosphere causing no detectable disturbances. It is used to destroy:
Playing Tip: Detonating the Probes around a star is considered an annoying act by many players but not one offensive enough to typically result in retaliation. However destroying Mining Platforms is regarded as a direct assault to many players and has a high chance of being retaliated against.
Some empires do like to occasionally detonate all the probes on stars near their planets and then watch to see what empires replace the lost probes. That way they can tell who has probes in the area. This loss of visibility is only a mild protection at best though as ships can still be sent to attack a planet that is not visible with a probe.