A mysterious incident over the southern Indian Ocean forced a U.S. Air Force aircraft to turn around due to an unnamed hazard in space.

According to several New Zealand-based news outlets, a U.S. Air Force (USAF) C-17 Globemaster transport aircraft left Christchurch Airport on New Zealand's South Island on Tuesday (Aug. 18) bound for McMurdo Station in Antarctica. Aircraft trackers using flight radar software noticed the C-17 turn around over the ocean some two hours into its flight.

According to a statement from New Zealand's Civil Aviation Authority given to the country's Stuff news outlet, the C-17 turned around after the Russian Air Traffic Management Corporation issued a notice advising of "space activity, potentially hazardous to aviation en route to Antarctica." It still remains unknown what that activity might have entailed, and the USAF has yet to issue a statement.

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