Scorched Earth Policy...

You big wussy!
If you dont want them to have the planet, kill em!

Just kiddin`

You could trade the planet to a weak minor civ for loads of cash...enemy doesnt benefit and its easier to reclaim.

Destroy the colony before they invade.

If you're going to gift the system to a minor civ, I recommend you load up the populace onto a combat transport. By doing so you give the minor civ a planet that isn't quite as productive, and a lot easier for you to take back

Or you could ue Terror Stars... LOL

when u see some freak with transport going to your planet u trade ur planet to someone who can really kick his ass

Go to the planet screen, click on the details button in the corner, and then click on the destroy colony screen. Voila, instant death for the billions of people that called that planet home...you horrible killer.

Or you could try to profit from the chunk of rock like other people have said by trying to sell it to someone you are on better terms with.

Or even better...sell it, then get ready to take it back

~SDC~