The Secret Life of Contrails

That white line behind a plane isn't smoke. It is an accidental cloud called

a contrail. Contrail is short for condensation trail. Jet engines release hot exhaust with

water vapor and tiny particles. Up high, the air is extremely cold,

so that water vapor can condense fast. As exhaust mixes with frigid air,

it can reach the conditions needed for cloud formation. The droplets freeze into countless ice

crystals almost instantly. Ice crystals scatter sunlight so the trail looks bright white.

Now the big question: why do some contrails vanish while others spread for

hours? The control knob isn't the plane. It is the air the plane