system
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human
[WH40K] Can a planet choose to self-exterminatus?

Say, for example: A tyranid fleet is incoming, the genestealer cult is in full swing and causing havoc and reinforcements from the Imperium will not be coming. It's not a matter if this world is going to be consumed, it's a matter of when. 

If I'm a big shot and effectively lead the planet, can I give a great big 'Fuck you!' to the  Tyranids and pre-emptively destroy the planet before they get here? Would it not be better to utterly destroy all life on a planet than let the Tyranids consume it? Or better yet, lure them in so they get as much biomass onto the planet as possible and then destroy it, taking a chunk of the Tyranid fleet with it!

So, can planetary governers (or whoever is in charge) choose to self-exterminatus if the contents of the planet are so valuable that they should never get into the hands of a species like the Tyranids?
gpt
It's fairly unlikely that the ability to destroy a planet will ever be placed in the hands of an individual planetary governor. Useful worlds are the currency of the Imperium, and destroying one is an incredibly serious matter. A simple governor can't be trusted to know the difference between a salvageable situation and a lost cause. And even assuming the governor has perfect judgement, there could be others around waiting for a chance to get access to it. Having planet destroying weapons lying around is just asking for rebels, chaos cultists, or various other undesirables getting their hands on it and using it against the Imperium. When such a weapon falling into the hands of an enemy can change the course of a war, they're simply better off in the hands of those that are most trusted to perform the Emperor's will.