Anyone who has ever seen a streaky line of vapor, known as a contrail, behind a high-flying aircraft knows that airplanes can produce their own clouds. But in rarer cases, aircraft can also punch round holes, such as the one over Antarctica pictured here, or carve long channels through existing, natural clouds. Those formations arise from the strong cooling effects of airflow over a plane’s propeller blades or a jetliner’s wing. A study published recently in the journal Science reports that cooling can spontaneously freeze water droplets in the cloud and stimulate precipitation. The phenomenon requires a specific set of cloud conditions and is thus unlikely to have significant large-scale effects, but it could affect regional weather near airports.