Behind any aircraft at hight altitude ''ex 30,000 ft" there is a white jet out from the A/C engines !

Question

What is that white jet ?
Where is coming from?
What is contains or requirment to have this white jet behind the engines??
What is the conditions to get this phenomena?
is it a 100% Fuel Burn to get a water condensation?

Answer 1

For a contrail to form, suitable conditions must occur
immediately behind a jet engine in the expanding engine
exhaust plume. A contrail will form if, as exhaust gases
cool and mix with surrounding air, the humidity becomes high
enough (or, equivalently, the air temperature becomes low
enough) for liquid water condensation to occur. The level of
humidity reached depends on the amount of water present in
the surrounding air, the temperature of the surrounding air, and
the amount of water and heat emitted in the exhaust.
Atmospheric temperature and humidity at any given location
undergo natural daily and seasonal variations and hence, are
not always suitable for the formation of contrails.
If sufficient humidity occurs in the exhaust plume, water con-
denses on particles to form liquid droplets. As the exhaust air
cools due to mixing with the cold local air, the newly formed
droplets rapidly freeze and form ice particles that make up a
contrail Thus, the surrounding atmosphere’s
conditions determine to a large extent whether or not a contrail
will form after an aircraft’s passage. Because the basic processes
are very well understood, contrail formation for a given aircraft
flight can be accurately predicted if atmospheric temperature
and humidity conditions are known.
After the initial formation of ice, a contrail evolves in one of two
ways, again depending on the surrounding atmosphere’s humid-
ity. If the humidity is low (below the conditions for ice conden-
sation to occur), the contrail will be short-lived. Newly formed
ice particles will quickly evaporate as exhaust gases are com-
pletely mixed into the surrounding atmosphere. The resulting
line-shaped contrail will extend only a short distance behind
the aircraft

Answer 2

The white contrail behind jet engines that you see is because it is extremely cold up at 30 thousand feet, and the trail of vapor that you see from an airliner waiting to takeoff turns white at this point...

Answer 3

May be a contrail, because the gas inside the aircraft is warmer than the air outside of the aircraft?

Answer 4

Dude, take a deep breath. It's called a contrail. Look it up.