File:Contrails over the Persian Gulf (MODIS 2024-12-23).jpg

English: Long, thin clouds marked the passage of dozens of airplanes over the Persian Gulf on December 19, 2024, when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired this true-color image. The image centers on the northern Persian Gulf, which is lined by Kuwait (west), Iran, and Iraq (east). The city of Basrah, Iran, can be seen in the upper left corner of the image.

The light-colored streaks across the sky are condensation trails (contrails) and are created by the exhaust of aircraft in certain atmospheric conditions. Contrails are a type of cirrus cloud that forms in nearly the same way as naturally occurring cirrus. The difference lies in the source of ingredients. Aircraft exhaust contains an abundance of water vapor and small particles. At high altitudes, where it’s cold enough—at least -39°C (-38°F)—the water vapor can easily freeze onto the particles and form these long, narrow clouds.

Contrails have been seen since the first airplane flights and are considered a normal feature of aircraft moving through humid, cold atmospheric layers. They may last just minutes or, in particularly favorable conditions, for several hours.