Variation of the lunar atmosphere with the strength of the solar wind

A simplified model of the lunar atmosphere is used to calculate average densities of seven different neutral gases and their ionized components, near the moon's surface, as a function of the solar corpuscular flux J. The method of calculation takes into account, in a unified way, the effect of sources of gas in the lunar crust as well as accretion by the solar wind, and the escape of gases by thermal evaporation and photoionization as well as interaction with the solar wind. For 107/cm2 sec < J < 109/cm2 sec, the main constituents of the lunar atmosphere are argon, constant at about 5 × 104/cm3, and neon, which increases linearly with J. For 109/cm2 sec < J < 1011/cm2 sec, argon and water vapor decrease with increasing J, whereas hydrogen, helium, and neon increase. For 1011/cm2 sec < J < 1013/cm2 sec, the densities of argon, neon, hydrogen, and helium take on the approximately constant values (independent of J) of 2 × 103/cm3, 2.8 × 105/cm3, 3.1 × 105/cm3, and 1.5 × 106/cm3, respectively. Hence, the total number density of gas from the sources considered will not exceed 2.1 × 106/cm3, regardless of how strong the solar flux may become. The densities of krypton and xenon will never be larger than 0.38/cm3 and 0.057/cm3, respectively. The only gases that contribute appreciably to the ionosphere are neon and argon.