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Credit: NASA Dryden Flight Research Center Collection
Contrails, or condensation trails, form when the plume of gases and soot emitted by a plane's engine interacts with cold air in the upper atmosphere to form ice particles. Later, the contrail loses its easily recognizable line shape and becomes a wispy cirrus cloud. Here, in a photo taken in 1970, new contrails stream behind the wings of a B-52 bomber and the smaller X-24A plane below it.