Dracotahl

new to game, quick question in Sins of a Solar Empire Sins Forums

ok I just started my first game. Looks good so far, but I'm discovering all these planets and asteroid belts with crystal or metal asteroids I would like to mine. I have complete control over the systems in question but have no idea how to go about building extractors in these new areas. Is there a time limit before I offically take control over the planet and can then start building there? I mean there is nothing left for me to attack so I'm a bit confused. Thanks