Here is the final, yet not optimal animation from my "30 seconds left"-image (
http://www.planetside.co.uk/forums/index.php/topic,16270.0.html)
It turned out that 30 seconds weren't enough time until the impact, so I increased it in the title.
I had to turn off "acceleration cache" for the first four or five cloud layers of the asteroid to avoid flickering issues in the fire/smoke trail. I should have turned it off in all layers. There's some heavy flickering in the rear part of the trail.
Anyway I don't want to improve this. Rendertimes were almost one and a half hours per frame, so I had enough...
Some postwork: lensflare, motion blur and chromatic aberration.
Didn't want to put it on Vimeo, because of the heavy blurring, so I decided to make it downloadable here.