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Jeans parameter

(ratio measuring a tendency of an atmosphere to escape)

The Jeans parameter is a measure of an atmosphere's tendency to escape (atmospheric escape) through a thermal escape mechanism (Jeans escape or hydrodynamic escape). It is a ratio of the kinetic energy of particles in the atmosphere with their gravitational potential energy. In a (virtually) spherically-symmetric situation, it is a function of distance from the center of the body. Certain thresholds have been devised to indicate whether escape would be significant.