JET SMOKE TRAIL

I am curious why do jets leave smoke trail in the sky? To answer my query I did a quick research from google and gotten these answers:

"What you are seeing is not smoke. It is a contrail . It is formed because the compressors in the jet engine compress a lot of air volume into an small chamber and the water vapor gets compressed into drops of water that are shot out of the back of the engine. The reason you see it at high altitudes is because the temp up there is around -40, those drops of water/vapor freeze instantly and form a cloud that you see witch is really thousands of water particles frozen. And to answer the other part only jet engines can do this because they have compressors, props do not so they cant make contrails. So if you are flying in a jet when the temp is a lot below freezing you will have a contrail. In some parts of Alaska and Siberia. The temp is already -20 and when planes take off they leave a contrail right there on the ground."
source: google