Abstract
AbstractIon escape is one of the key processes responsible for drastic climate change on ancient Mars. Ion escape is affected by the solar X‐ray and EUV (X‐ray and extreme ultraviolet (XUV)) flux, the solar wind, and the presence of a planetary intrinsic magnetic field, all of which was much different at ancient Mars. We investigated how the presence and strength of a dipole field affects the ion escape under 50 or 10 times higher solar XUV flux and strong solar wind with multispecies magnetohydrodynamics model. The results showed two opposite effects on the escape rates, which is associated with the pressure ratio of the dipolar magnetic pressure at the equatorial surface to the solar wind dynamic pressure. The escape rates increase by up to a factor of 6 for O2+ and CO2+ but change little for O+ if the pressure ratio is below 0.1. On the other hand, the escape rates decrease by more than one order of magnitude for the three ions if the pressure ratio is above 0.1. The threshold can be described by the pressure balance between the solar wind flow and the dipole field at high latitudes, where the ionospheric outflow emerges in the unmagnetized cases. The effects on the escape rates are stronger under lower solar XUV cases. The total escape rate reaches 1027 s−1 in the unmagnetized case, which may lead to a large contribution to atmospheric loss at ancient Mars, but it can be reduced by an order of magnitude in the presence of a dipole field.
Published Version
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