Vehicle that, per ScienceNews, "would stress out a bear" (3)

I believe the answer is:

ufo

(Other definitions for ufo that I've seen before include "Saucer in the sky?" , "Initially and formally, flying saucer" , "ET transporter?" , "Odd object in the sky" , "Mysterious sighting" .)

I've seen this clue in the USA Today.

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