I let a TX3 auton explore a system until it had "No unexplored objects in system".
But it hadn't found the Acheron stargate which was near a Mining Colony that it did discover (top centre of second image).
Using a system map ROM brought the stargate up, no problem.
I don't know if this is intentional but I personally would greatly prefer to have the autons find the stargates as well.
Ferdinand (I think) gets credit for spotting this.