Protoplanetary disk affected by photoevaporation due to the proximity of an O-type star. The photoevaporation designates the process by which a planet is stripped of its atmosphere or part of it due to the interaction of it with highly energetic photons and other types of electromagnetic radiation. When a photon interacts with a molecule belonging to the atmosphere, that molecule is excited, its speed and temperature are increased. If sufficient energy were transferred, that atom or molecule could reach the escape velocity of the planet and "evaporate" into space, that is, escape from the atmosphere and the gravitational attraction of the planet. The lower the molecular mass of the gas, the greater the velocity resulting from the interaction with the radiation. Thus, hydrogen is the most prone to photoevaporation. Photoevaporation in protoplanetary disks
Protoplanetary disks can be dispersed by stellar wind and / or heating, due to the incidence of electromagnetic radiation. The discs are formed of gas and dust and, since the gas is composed of very light elements such as hydrogen or helium, it is the gas that suffers the most photoevaporation. The acceleration of the bodies caused by the radiation favors the exit of the particles from the disc towards the outside. This effect is only appreciable when the radiation is sufficiently energetic, such as that from nearby stars of type O or type B, or also when nuclear fusion begins at the central protostar.
wiki
