Fighter jets shot one down but say the last three are different from an alleged Chinese spy balloon.
Pentagon officials say they're "not ruling anything out" when asked if "aliens or extra-terrestrials" could be behind a fourth object found flying over North America.
Fighter jets shot this one down over Michigan - but say the last three are different from an alleged Chinese spy balloon at the beginning of the month.
A security review has been launched in the UK as a result.
Sky's US correspondent James Matthews has the latest:
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