The white streaks you see coming off high-flying jet airplanes are called contrails, which is short for condensation trail. Contrails are clouds that formed when water vapor condenses and freezes around small particles that exist in aircraft exhaust. The water vapor comes from the air around the plane and the exhaust of the aircraft.

Some contrails evaporate quickly while others stay in the sky for a long time after the airplane is gone. These contrails can become human-made cirrus clouds. Contrails last longer when there is a greater amount of water in the air; they last until the water in the clouds evaporates.

There are three types of contrails: short-lived, persistent non-spreading, and persistent spreading.