it is noticable already during the events in the Isstvan campaign that Horus himself enters a bit a of a tunnel vision, he is starting to miss little details, and for example fails to predict that Angron would personaly fly down to take on his legions stragglers on the surface.
asside from that, they probably made a direct push for Terra as soon as they entered the Sol system, all focus and attention was on Terra itself, and most likely on Mars. compared to those 2 most likely heavely fortified planets, and the militarized Luna, I doubt they paid much attention to the other planets.
especialy an uninhabitted gas giant.
tho I dont know for sure if any of the moons besides Luna have ever been propperly colonised.
on another note as I mentioned. Saturn is a gas giant, wich probably means that any attempts at sensor scanning anywhere near the planet, would be interfered by radiation of different kinds
Last edited by Haskanael; 02-21-14 at 05:49 AM.