The mesosphere is the coldest layer within Earth’s atmosphere. It is characterized by temperatures that plunge to extreme lows.
Earth’s Atmospheric Layers
Earth’s atmosphere is organized into distinct layers. The layer closest to the surface is the troposphere, extending up to about 15 kilometers (9 miles). Within this layer, temperature decreases with increasing altitude, and it is where most weather phenomena occur.
Above the troposphere lies the stratosphere, reaching an altitude of about 50 kilometers (31 miles). Unlike the troposphere, the temperature within the stratosphere increases with height. This warming is primarily due to the ozone layer absorbing ultraviolet radiation from the sun. Following the stratosphere is the mesosphere, spanning from about 50 to 85 kilometers (31 to 53 miles). Beyond the mesosphere are the thermosphere and the exosphere, where temperatures begin to rise again due to the absorption of high-energy solar radiation, though the air density is extremely low.
Why the Mesosphere is the Coldest
The mesosphere experiences the coldest temperatures in Earth’s atmosphere due to air density and radiation absorption. As altitude increases within the mesosphere, the density of air molecules significantly decreases. This scarcity of molecules means there are fewer particles available to absorb incoming solar radiation and retain heat.
Unlike the stratosphere, the mesosphere contains little ozone, which absorbs ultraviolet radiation and warms the stratosphere. This lack of heat absorption contributes to the temperature drop. Carbon dioxide, a warming greenhouse gas in the lower atmosphere, efficiently radiates heat into space in the rarefied mesosphere, further cooling it. Temperatures in the upper mesosphere can fall to -90 degrees Celsius (-130 degrees Fahrenheit). The coldest point, the mesopause, can reach -173 degrees Celsius (-225 degrees Fahrenheit).
Phenomena in the Mesosphere
The mesosphere is notable for several distinct phenomena. This layer is where most meteors, commonly known as “shooting stars,” burn up upon entering Earth’s atmosphere. As meteoroids encounter the increasing density of gases in the mesosphere, friction with air molecules generates intense heat, causing them to disintegrate and create visible streaks of light.
Another striking phenomenon observed in the mesosphere is the formation of noctilucent clouds, also referred to as polar mesospheric clouds. These ethereal, shimmering clouds are the highest clouds in Earth’s atmosphere, typically forming at altitudes between 76 and 85 kilometers (47 to 53 miles). They are composed of tiny ice crystals that form on minute dust particles, possibly originating from meteoric debris. Noctilucent clouds are best seen during twilight hours in summer at high latitudes when they reflect sunlight from below the horizon, glowing with a distinctive bluish or silvery hue against the dark night sky. Their formation requires extremely cold temperatures, below about -120 degrees Celsius (-184 degrees Fahrenheit), which are found in the mesosphere during summer.