No, those trail are not the smoke from the plane engine. They are called Contrails, shortened for condensation trail. The science behind it is same as on certain days in winter when you exhale you can see your breath.
Jet fuel is actually made of carbon and hydrogen. When it burns with oxygen, CO2 is formed along with H2O. When this water mixes with the wet cold air, it condenses and ice crystals are formed. How long will these contrails last depends on how wet and cold is the surrounding air. When the conditions are pleasant, they spread across to look like Cirrus clouds.
Now, why do only few planes leave contrails?
1. Altitude - Contrails usually form at altitude above 20000 feet where the air is at -40 to -60 degree Celcius.
2. Engines - Some engines leave contrails and some don't.
3. Dry air - Contrails are not formed when the air is dry.
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