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Jeans escape (or Jeans gas loss) is loss of part of an atmosphere due to some molecules being at escape velocity simply for being within the higher-velocity end of the Maxwell-Boltzmann distribution. The latter is the distribution of speeds of the particles making up a gas due to their bouncing off each other: the distribution features a most-probable speed (a peak in the distribution) with decreasing probability ("tails") according to how much faster or slower than this peak, but while the probability can be small, no speed (below the speed of light) has zero probability and a particle can reach the escape velocity. Jeans escape is a type of thermal escape, i.e., escape of molecules due to the atmosphere's temperature. Losing gas in the manner is also referred to as boiling off.