WHILE DRIVING STRAIGHT ON THE FREEWAY AT ABOUT 70MPH THE FRONT HALF OF OUR 'PANORAMIC' SUNROOF 'EXPLODED' FROM THE INSIDE OUT AS IF FROM CABIN PRESSURE. THE REMAINING GLASS WAS BLOWN UPWARDS. THERE WERE NO OTHER VEHICLES NEARBY NOR WAS THERE ANYTHING ABOVE OUR VEHICLE WHEN THIS OCCURRED. THERE WAS NO EVIDENCE OF A PROJECTILE IN OR AROUND THE VEHICLE.