Is it possible to destroy planets (or to damage them, or to harm a planet's environment)? I didn't see anything like that in the downloadable tech tree, but it doesn't say what the techs unlock, so... Do the more advanced weapons techs make planet destruction possible, or is it not possible, or does some other tech entirely make it possible?
"For it must be noted, that men must either be caressed or else annihilated; they will revenge themselves for small injuries, but cannot do so for great ones; the injury therefore that we do to a man must be such that we need not fear his vengeance." - Niccolo Machiavelli
It's not possible to destroy planets. It's possible to lower it's planet quality during a successful invasion, but someone stated that this applies only to your own race, if someone else conquers it the PQ will be reset, which would make it useless in that regard.