Sun Roof problems of the 2006 Mercedes Benz E350

I was driving my mercedes E350 on the highway at 60 mph when I heard an explosion. The sunroof had exploded while I was driving and showered glass shards into the interior. Most of the glass landed in the rear of the vehicle. We could not find any rocks or the like inside the vehicle afterwards. Anyone who had been in the back seat would have been injured by the very sharp glass fragments. Although I was extremely startled I was able to keep control of the vehicle. I don't know if a rock broke through the glass or whether the glass simply exploded.