The regulation of hydrogen and oxygen escape from Mars

It is shown that under present conditions the Jeans escape flux of hydrogen from Mars in the form of H and H₂ is constrained to be the same as twice the non-thermal (McElroy, 1972) escape of O atoms. The mediation of the chemical chain that recombines CO₂ plays an essential role in regulating the escape of hydrogen to match that of oxygen, confirming a mechanism postulated by McElroy and Donahue (1972). It is also shown that if the oxygen flux changes, a change in the O₂ mixing ratio results and the consequence is to induce a large change in the odd hydrogen concentration, and consequently in H₂ production and hydrogen escape. The effect is to stabilize the hydrogen escape flux at twice the O flux. It is shown that surface chemistry should not change the operation of this mechanism but has consequences for the eddy coefficient variation at low altitudes. There is a strong correlation between low humidity, large solar zenith angles and large O₃ abundances. The effect of argon in a mixing ratio as large as 0.3 on these results is also investigated.