Planes do not fly in the mesosphere. Earth’s atmosphere has distinct layers, and aircraft operate within specific regions. Conditions in the mesosphere are too extreme for conventional flight, making it inaccessible for all but specialized scientific instruments.
Earth’s Atmospheric Layers
Earth’s atmosphere is stratified into five primary layers: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Each layer is characterized by unique temperature profiles, gas compositions, and densities. The troposphere, extending from the Earth’s surface up to about 12 kilometers (7.5 miles) on average, is where almost all weather occurs and where the air is densest. Temperatures in the troposphere generally decrease with increasing altitude.
Above the troposphere lies the stratosphere, reaching an altitude of roughly 50 kilometers (31 miles). This layer contains the ozone layer, which absorbs ultraviolet radiation from the sun, causing temperatures to increase with height. The mesosphere is the next layer, extending from about 50 to 85 kilometers (31 to 53 miles) above the surface. In this region, temperatures decrease significantly with altitude, making its upper boundary the coldest part of Earth’s atmosphere.
The thermosphere, located above the mesosphere, stretches from approximately 85 kilometers (53 miles) to about 600 kilometers (375 miles). Temperatures here can rise dramatically due to the absorption of high-energy solar radiation, though the air is extremely thin. Finally, the exosphere is the outermost layer, where the atmosphere gradually fades into space, with atoms and molecules eventually escaping Earth’s gravity.
Where Aircraft Typically Fly
Commercial airliners primarily operate within the troposphere and lower stratosphere. Their cruising altitudes range from approximately 9,100 to 12,800 meters (30,000 to 42,000 feet). This range offers optimal fuel efficiency due to reduced air density and allows aircraft to fly above most weather disturbances and turbulence.
Private jets often fly at slightly higher altitudes than commercial airliners, typically between 12,500 and 15,500 meters (41,000 and 51,000 feet). This allows them to avoid congested airspace and experience smoother flight conditions. Military aircraft, such as fighter jets and reconnaissance planes, can reach greater heights. Some fighter jets operate up to 18,300 meters (60,000 feet), and specialized reconnaissance aircraft like the U-2 spy plane routinely fly above 21,300 meters (70,000 feet), with some experimental military aircraft reaching up to 25,900 meters (85,000 feet). These ceilings place all conventional aircraft below the mesosphere.
Why Planes Don’t Fly in the Mesosphere
Conventional aircraft cannot fly in the mesosphere due to low air density. At these altitudes, the air is too thin to generate sufficient lift over a plane’s wings. Aircraft rely on the interaction between their wings and a dense flow of air to create the upward force necessary for flight.
Jet engines require a certain air density to function properly. They operate by taking in air, compressing it, mixing it with fuel, and igniting the mixture. The scarcity of air molecules in the mesosphere means there is not enough oxygen to support combustion. The air pressure at the bottom of the mesosphere is less than 1% of the pressure at sea level and continues to decrease with altitude.
Temperatures in the mesosphere drop to as low as -90°C (-130°F) or even -100°C (-148°F) at its upper boundary, the mesopause. While cold can improve engine efficiency by increasing air density (at lower altitudes), the lack of air molecules at mesospheric heights renders conventional engines ineffective. The absence of an ozone layer in the mesosphere would also expose any craft to high levels of ultraviolet radiation.
Phenomena in the Mesosphere
Despite being unsuitable for conventional aircraft, the mesosphere is a dynamic layer where several natural phenomena occur. This is the region where meteors burn up as they enter Earth’s atmosphere. Friction between rapidly moving space rocks and increasing gas density causes them to heat up and disintegrate, creating visible streaks of light known as “shooting stars.”
The mesosphere is also home to noctilucent clouds, the highest clouds in Earth’s atmosphere. These wispy, bluish-silver clouds are composed of tiny ice crystals that form on dust particles, possibly from micrometeors, at low temperatures, often below -120°C (-184°F). They are visible during summer at high latitudes when sunlight illuminates them from below the horizon after sunset.
Scientific research instruments, particularly sounding rockets, study the mesosphere directly. These suborbital rockets launch into and through the layer, collecting data on its composition, temperature, and dynamics before returning to Earth. This method provides insights into this region, which is too high for weather balloons and too low for orbiting satellites.