Knowra Planetary atmosphere Planetary atmosphere A layer of gases gravitationally bound to a planet. Its pressure, temperature, and composition vary with altitude and shape climate, weather, and surface conditions.
Hydrostatic equilibrium : A balance in which pressure gradients support a fluid against gravity. Atmospheric pressure generally falls with altitude because it supports the weight of overlying gas.
Atmospheric pressure : The force per unit area exerted by the weight and motion of atmospheric gas. Pressure measures the overlying gas and declines upward through the atmosphere.
Planetary habitability : The capacity of a planetary environment to support life, especially liquid-water life as known on Earth. Atmospheric pressure and composition help determine whether surface liquid water can persist.
Earth's atmosphere : The nitrogen- and oxygen-rich gaseous envelope surrounding Earth. Earth's atmosphere is a familiar case with a surface, active weather, and abundant liquid water.
Atmospheric erosion : The removal of atmospheric gas by processes such as stellar wind, radiation, and particle escape. Long-term erosion can transform a planet from a gas-rich world into an airless or thin-aired one.
Atmospheric escape : The loss of gas from an atmosphere into space. Escape determines whether a planet retains light gases over geological time.
Atmospheric temperature : A measure of the thermal state of atmospheric gas at a given location and time. Temperature controls density, circulation, and the ability of gas to escape.
Planetary climate : The long-term statistical pattern of temperature, circulation, and other environmental conditions on a planet. Atmospheric energy transport and greenhouse gases are central to climate.
Venus atmosphere : The dense, carbon-dioxide-dominated gaseous envelope surrounding Venus. Venus demonstrates how high pressure and an intense greenhouse effect shape a rocky planet.
Runaway greenhouse effect : A positive feedback in which warming increases greenhouse trapping until a planet's surface becomes extremely hot. It describes a possible climate endpoint for atmospheres with strong water-vapor feedback.
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