The US military is in a state of "heightened alert" over unidentified objects flying in its airspace, with no less than four of them having been shot down in the past eight days.
Only the first one of those, a white balloon determined to be a surveillance object sent from China, has been identified as of yet, while the origin of the rest remains a mystery as of yet.
But it is not the first time that the Pentagon is faced with unexplained floating objects in its airspace and officials struggle to come up with an explanation.
