Apassenger jet flying at cruising altitude is often traveling in the upper troposphere at approximately 725 km per hour (or 450 mph). why don't passenger jets burn up as meteors do?

Explanation:

Objects like meteors travel at high rates of the speed and thus, possess large amounts of the kinetic energy.  As the meteors enter Mesosphere, they enter more dense segment of earth's atmosphere with the greater numbers of the gas molecules.  Meteors which encounter the large numbers of the gas molecules at the high rates of the speed and generate large amounts of the friction in process. As a result, enormous heat is built up. This build-up of heat  ultimately causes the fast-traveling meteors to burn up in atmosphere.

While passenger jets travel at very small speed as compared with the speed of the meteors and don not burn.