While driving southbound at about 55 mph on a smooth level divided highway on a clear day with a temperature of about 45 degrees my moon roof exploded. Both the glass portion and the inner sliding cover were closed. There was a loud "wham, " and then a rattling sound that turned out to be the shards of class bouncing around on the inner sliding cover. No debris other than the glass was inside the roof, and we checked 100 yards back in the direction from which we came and found nothing that could have hit us from above. Luckily, there was a Subaru dealer nearby, and we were able to continue our vacation with a loaner while they fixed the moon roof. We took the opportunity to replace a lost "smart key" at the same time, and that is reflected on the attached bill but has nothing to do with this event. We were uninjured, but had the inner sliding cover been open, we would have been showered with broken glass while driving at highway speed.

- Belchertown, MA, USA