What causes jet streams?

Jet stream is the gas that comes back from a jet engine. When a jet takes off, you may see a stream of white gas flowing behind the jets. This is normal. It is called contrails. Contrails usually consist of water and ice. It is projected out the back of a jet. Some jets leave long contrails whereas others leave short contrails. Others don’t leave any contrails. Instead of being jet fuel, this jet stream is actually water and ice.

They are created when this water that is in the exhaust and forms ice crystals when it becomes mixed with the cold air. Then this stream of icy water is shot out the end of the jet. The length of the contrails depends on the amount of water and ice that has formed.