Just a hunch....in the leaked trailer it looks like what's firing down on the crew aren't rockets or bombs but whatever is in those urns?Consensus of opinion was that it's more likely just random debris raining down from the crashing ship.
Many assumed it was an Engineer ship, but it could just as easily have been a human craft.
It could be two completely different moments that are shown in the trailer. Firstly it shows the derelict, then people running from an massive encroaching shadow, then a shot shows that they are running from something that could be the derelict, and then the shot in question looks like something else altogether.
The object in the last frame doesn't seem to fit with the object shown in the proceeding two.
EDIT: There actually are some similarities