I'm hearing this from a number of sources, including NASA itself.

Another article speculates that a meteor or other debris might have been the culprit.

What is the standard orientation of the Shuttle in orbit when no docking or other maneuvering is taking place?

I have heard that the Shuttle often flies in the second "vertical" configuration above (LVLH). Base forward in the direction of orbit. If so, it is likely that any orbital debris would strike hard from the direction of the base.

This shot appears to be taken through the cockpit "ceiling" windows, which would imply that at least when this shot was taken, the Shuttle was flying in a "vertical" configuration.

If there was an impact sufficient to damage the wing, one would think the vibration would rattle the whole vehicle. On the other hand, the reaction jets thump pretty good too, and maybe nobody would have noticed.

Input?