WASHINGTON, Feb 12 (Reuters) - U.S. military fighter jets on Sunday shot down an octagonal object over Lake Huron, the Pentagon said, the latest incident since a suspected Chinese surveillance balloon put North American security forces on high alert.....U.S. Air Force General Glen VanHerck, who is tasked with safeguarding U.S. airspace, told reporters that the military has not been able to identify what the three most recent objects are, how they stay aloft, or where they are coming from.....We're calling them objects, not balloons, for a reason," VanHerck, head of North American Aerospace Defense Command (NORAD) and Northern Command, said. VanHerck said he would not rule out aliens or any other explanation.