What are the dotted colored rings around the planets for?

[GhoulMX]

I already finished the tutorial. I dont remember (if I remember correctly  ) if the tutorial explained what those rings meant.   I am such a noob at this game still, but I am loving it.   

[Hearteater]

Those are the gravity wells. The inner (green) ring is the maximum distance you can build structures (such as turrets). Beyond the green ring only mobile units can travel, but their speed is greatly reduced. They can travel as far as the yellow ring. The yellow ring is the absolute boundary.

[GhoulMX]

Thank you very much Hearteater... that makes a lot of sense.