Photoevaporation

Photoevaporation is the heating and dispersal of material when radiation causes gas to escape from a surface or cloud. It occurs in settings ranging from planetary atmospheres to irradiated interstellar clouds.

Photoionization: Photoionization occurs when a photon removes an electron from an atom or molecule. Ionizing photons often supply the heat that drives gas out of an irradiated cloud.
Atmospheric escape: Atmospheric escape is the loss of gas from a planet or moon into space. Photoevaporation is one radiation-driven route by which planetary atmospheres escape.
Radiative transfer: Radiative transfer describes how radiation is emitted, absorbed, and scattered as it travels through matter. It determines how deeply the heating radiation penetrates the gas or surface.
Core-powered mass loss: Core-powered mass loss is atmospheric escape driven by heat remaining in a planet’s cooling interior. It can strip planetary envelopes without requiring stellar radiation to power the outflow.
Hydrodynamic escape: Hydrodynamic escape is the bulk outflow of an atmosphere driven by pressure gradients and heating. It describes the collective gas flow that can carry away photoheated material.
Hot Jupiter: A hot Jupiter is a gas giant orbiting very close to its star, with a strongly heated atmosphere. Some hot Jupiters show extended atmospheres losing gas under stellar irradiation.
Thermal equilibrium: Thermal equilibrium is a state in which energy gains and losses balance, leaving temperature steady. Heating and cooling rates set the temperature that drives or suppresses gas escape.
Magnetically driven wind: A magnetically driven wind is an outflow accelerated by magnetic forces acting on conducting gas. Magnetic acceleration offers a different driver from radiation heating.
Jeans escape: Jeans escape is the loss of fast individual particles from the high-speed tail of a gas distribution. It contrasts with photoevaporation’s often collective, radiation-driven outflow.
Hot Neptune desert: The hot Neptune desert is the observed scarcity of Neptune-sized planets on very short-period orbits. Photoevaporation is one explanation for why close-in planets lose much of their gaseous envelopes.

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