ALL CREDIT GOES TO NILAUS
Planet "defense?" system used by Nilaus to deter the Dark Fog.

FULL EXPLANATION
The signal towers allow for missile turrets anywhere on the planet to shoot anywhere inside the signal tower's range. So by placing them all around the planet the moment any Dark Fog land (if at all) they will get nuked assuming you have a lark collection of missile turrets somewhere. Global Defense. Pairing this with PSG's (Planetary Shield Generators) would also allow for defense against space attacks but is not included and probably wastes more resources than it is worth.