Suffice to say, a lot.

Personally, I have a hard time believing you're actually nuking/blasting a planet to dust, since then terran planets would be effectively useless after the first wave of bombardment. Not to mention the fallout that TEC bombardment would cause and all the other potential problems you have with saying "**** it, let's just blow everything to pieces".

Then again, this is also a game that features lasers that move slower than autocannon shells, so maybe it doesn't really matter very much.