The answer to whether planes fly in the mesosphere is definitively no, because the physical conditions of this atmospheric layer make both aerodynamic lift and engine combustion impossible. Aircraft rely on the presence of sufficient air molecules found closer to the ground. The extreme lack of air density at the mesosphere’s altitude prevents the generation of the necessary forces required to keep a plane airborne and to feed an air-breathing jet engine. This fundamental limitation creates a significant altitude gap between the highest-flying aircraft and the start of the mesosphere.
What Defines the Mesosphere
The mesosphere is the third major layer of Earth’s atmosphere, situated directly above the stratosphere. It begins at an approximate altitude of 50 kilometers (31 miles) and extends upward to about 85 kilometers (53 miles) above the planet’s surface. This region is characterized by a rapid drop in temperature as altitude increases. The top boundary, known as the mesopause, contains the coldest temperatures found anywhere in the atmosphere, often plunging to around -90 degrees Celsius (-130 degrees Fahrenheit).
Air density in the mesosphere is exceptionally low, dropping to less than one percent of the pressure felt at sea level. This layer is too high for weather balloons and conventional aircraft to reach, yet too low for satellites to maintain stable orbits, making it a difficult region for scientists to study directly.
Where Air-Breathing Aircraft Operate
The operational zone for nearly all air-breathing aircraft, including commercial airliners and military jets, is the troposphere and the lower portion of the stratosphere. Commercial jets typically cruise between 9 kilometers (30,000 feet) and 13.7 kilometers (45,000 feet), where the air temperature is relatively stable and drag is reduced. This altitude is well within the troposphere and the lower stratosphere, which extends up to about 50 kilometers.
Sustained flight requires two simultaneous conditions to be met by the surrounding atmosphere. First, the air must be dense enough to flow over the wings and create aerodynamic lift, which counteracts the force of gravity. Second, jet engines require a continuous supply of oxygen molecules, which are drawn from the surrounding atmosphere, to support the combustion of fuel. Air pressure drops exponentially with altitude, meaning the air becomes rapidly thinner as a plane climbs.
The Ultimate Altitude Limits of Flight
The physical ceiling for air-breathing aircraft is determined by the point where the decreasing atmospheric density can no longer meet the dual demands of lift and combustion. As a plane climbs higher into the stratosphere, the air eventually becomes too tenuous for wings to generate adequate lift without an impractical increase in airspeed or wing size. Simultaneously, the amount of oxygen molecules captured by the engine inlet drops to a level that starves the combustion process, limiting thrust.
Specialized reconnaissance aircraft demonstrate the technical limits of this ceiling, operating at the very top of the stratosphere. The record for sustained flight by a jet-powered aircraft, for example, was set by the SR-71 Blackbird, which achieved altitudes around 26 kilometers (85,000 feet). Other high-altitude aircraft, such as the U-2, typically cruise around 23 kilometers (75,000 feet).