evidence: The latest object - shot down over Lake Huron in Michigan near the Canadian border - has been described by defence officials as an unmanned "octagonal structure" with strings attached to it. [...] President Biden ordered an object to be shot down over northern Alaska on Friday, and on Saturday a similar object was shot down over the Yukon in north-western Canada. [...] Unidentified flying objects - timeline 4 February: US military shoots down suspected surveillance balloon off the coast of South Carolina. It had drifted for days over the US, and officials said it came from China and had been monitoring sensitive sites 10 February: US downs another object off northern Alaska which officials said lacked any system of propulsion or control 11 February: An American fighter jet shoots down a "high-altitude airborne object" over Canada's Yukon territory, about 100 miles (160 km) from the US border. It was described as cylindrical and smaller than the first balloon 12 February: US jets shoot down a fourth high-altitude object near Lake Huron "out of an abundance of caution"