Right. I believe it was insulating foam from one of the fuel tanks IIRC. You can bet that it will be scrutinized now.
My theory (think hindenburg)
The insulation that came off of the fuel tank during liftoff left a weak spot. The ship was not fully protected from static electricity.
Upon re-entry, the now weakened ship traveled through atmosphere that was heavily charged with electricity. A wayward lightning bolt found its way to ground itself on the fuel tank...
This is just terrible.
