A mission type in which a fleet will attempt to take over the attacked colony. Your fleet will have to be able to quell all rebels that will result from the attempted conquering because colonists are generally loyal to their leader and unwilling to go gently into that good night.

Please be aware that gravity affects the size of ships that can actively attack ground defenses at a colony.

4000 / Planet Gravity = tonnage limit
e.g. 4000 / 10.0 = 400 tons

Beware that conquering a colony is very destructive business and much of the colonial assets will be lost in the struggle. Further, much of what remains will only be wreckage which only your tech sector will be able to use. If you already have assets on the same planet, assimilating foreign land can wreak havoc on your development.