In late February, 2012, ships traveling over the Pacific Ocean off the coast of the western United States etched their movements in the sky above them, leaving trails of bright white clouds to mark their oceanic wanderings. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite captured this true-color image of ship trails in the sky on February 21, 2012.
Clouds are formed when water vapor condenses onto a small particle, such as dust or a salt crystal. Ships burn fossil fuel, and emit small aerosol particles which can effectively act as a nucleus for cloud formation.
While ships travel in this region constantly, clouds do not always form over their tracks. In order for such clouds to form, three things must occur. First, the ship must emit small particles in the exhaust, which provide the cloud condensation nuclei. Second, there must be very humid air in the ship’s path, and third, the air surrounding the vessel must be non-turbulent. All three conditions were met on the day this image was captured.