My wondering- Why do aeroplanes make tracks in the sky?

Jets burn like cars do. Like cars they have exhaust which is the gas that is created when an engine burns fuel. One of the chemicals in the exhaust is called water vapor. When the exhaust escapes from the engine it leaves a trail in the sky. It is very cold in the sky so the stripes that the jets leave are cooled water and iced crystal. The water droplets are very light so they float in the sky. The technical name for these stripes is contrail or vapor trail. They are made by jets.