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White Trails in the Sky Are Formed by Ice Crystals, Resulting from the Condensation of Steam from Turbines at High Altitudes
It looks like smoke, but it’s not. The white trails left by airplanes in the sky are formed by the condensation of water vapor, like small artificial clouds. The phenomenon has a technical name: condensation trail or contrail. In English, it is called “contrails.”
These trails usually appear when the airplane flies above 8,000 meters, where temperatures can drop to -50ºC. In this cold environment, there is an intense thermal contrast with the hot gases exiting the turbines, which exceed 300ºC.
How the Trail That Looks Like Smoke Is Formed
As they exit the turbines, the hot gases come into contact with the extremely cold air at altitude. This encounter causes the rapid condensation of water vapor, which turns into small droplets.
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Shortly thereafter, these droplets freeze and turn into ice crystals. The result is the white trail we see cutting across the sky.
The appearance of the trail can vary. On colder and more humid days, it tends to be larger and last longer. In drier atmospheres, the trail disappears quickly.
In addition to ice, these trails may also contain residues from fuel combustion, such as soot and sulfur dioxide.
Historical Records
The first observations of this phenomenon occurred shortly after World War I. In 1919, during a flight in Munich, Germany, a condensation trail was recorded when the aircraft reached an altitude of over 9,200 meters. From then on, trails became common as airplanes began to fly higher.
Although they look like polluting smoke, the trails are mainly composed of water in solid state, in the form of ice crystals.
Information from UOL.
