An AI fleet containing 3 Teros Heavy Cruisers (and one troop ship) headed for Deneb my only colony with a Space Station, that had just built a Human Light Cruiser. 1 on 1, a Human Light Cruiser can take on the Teros ships, but I did not have any deflectors (big problem!), and they outnumbered me 3:1. My fleet was off attacking one of their colonies, and would not arrive for many turns. I feared the worst when the Teros arrived, that they would blow my CL out of the sky, destroy my Space Station, and bomb my 2nd best manufacturing colony into the stone age.
Upon arrival, I got a notification of a "Teros Encounter at Deneb". I opted NOT to begin a battle I knew I could not win. With trepidation I hit "Next Turn".
...And nothing happened. No invasion, no bombardment, no destruction, NO ATTACK! In fact, the Teros were redeploying one of their Heavy Cruisers back to a home system, leaving just 2 to threaten me.
A quicksave test battle showed me that I was a fool to even consider attempting to drive them away. I just barely penetrated their shields before being torn to ribbons by their Ion Beams. Even with 2 Heavy Cruisers, I was still in mortal danger. With some minor worry, I hit "Next Turn" again.
...No attack. In fact, ANOTHER Heavy Cruiser departed, leaving only one left to face me. I'd still lose, but my fleet was going to arrive next turn. I fought a small battle, destroying a Scout Cruiser before retreating my ship, and hit "Next Turn".
All Teros Ships have now departed the Deneb system. (Interestingly, my damaged Light Cruiser retreated BACK to Deneb from Deneb. Is this intended for defender retreats?)
The entire Teros attack has amounted to NOTHING. They never initiated a battle when they had superiority, and instead withdrew their ships from the system. Were they afraid of my Light Cruiser, or was this the result of poor planning on the AI's part. It LOOKS as though this was supposed to be an invasion, but when they arrived, they saw they didn't have the forces to take my planet, and so just decided to go home. Does the AI ever mount successful invasions?