perhaps it could be heading for a stationary target like a spacedock or starbase and would require a small fleet to destroy it.
Great ideas and i will put the ideas into account.
I might make a map pack to go with it (probally ask chris jones for help) and there could be a A.I in the system that the asteroid/Comet does do a collision course with a planet. But working on planet damage will be hard but i will look into it.
Thank you all for your ideas and keep them coming.