atmosfære

Atmosfære, in planetary science, is the layer of gases that surrounds a celestial body and is retained by gravity. On Earth it blankets the surface and fades into space; most of its mass is within the first 10–20 kilometers, though trace amounts extend much higher. Its composition varies by body, but Earth’s atmosphere is dominated by nitrogen (~78%) and oxygen (~21%), with argon, carbon dioxide, neon, helium, methane and water vapor making up the rest. Water vapor concentration varies with location and time and strongly influences weather and climate.

Structure and function: The atmosphere is structured into layers defined by temperature trends: the troposphere, stratosphere, mesosphere, thermosphere and exosphere. The troposphere contains most weather and clouds and ends at the tropopause; the stratosphere holds the ozone layer that absorbs UV radiation. The atmosphere regulates surface temperature, provides breathable air, shields life from harmful radiation, and drives weather systems and climate through wind, precipitation and radiant heat.

Variability and impact: Atmospheric pressure, composition and temperature change with altitude, latitude and season. Human activities alter the atmosphere by emitting greenhouse gases, aerosols and pollutants, contributing to climate change, air quality changes and ozone depletion in some regions. Studying atmospheres—via spectroscopy, weather satellites, balloons and probes—helps understand planetary environments, climate history and the potential habitability of other worlds. Other planets and moons show a wide range of atmospheres, from thin CO2 envelopes on Mars to dense nitrogen-oxygen or hydrogen-helium atmospheres on outer planets.