Because they form at such cold temperatures, the water vapor in the cloud freezes. The crystals inside these clouds will reflect sunlight and make some very interesting effects. Rainbows and color halos are frequently seen in and around cirrus clouds. As I said earlier, a contrail is simply a cirrus cloud. But instead of forming naturally, it has a little help from an airplane.
Airplane contrails only form under certain conditions.
O C. Second, the airplane must supply moisture for the cloud to form. This moisture comes from airplane exhaust. As the plane burns jet fuel, it spews out carbon dioxide and water vapor. It is this vapor that forms the contrail as it freezes. The lifespan of a contrail is entirely dependent on the amount of moisture already present in the atmosphere.