ON THE ORIGIN OF THE TAILWARD VELOCITY OF O+ IONS OVERTHE MAGNETIC POLES OF MARS

摘要

We numerically simulate the dynamics of a population of 0+ ions of iono-spheric origin picked-up by the solar wind in the dayside ionosheath of Mars. Theiraverage velocity as they] each the magnetic polar regions of the planet is comparedwith in situ measurements of the Mars Express spacecraft. We find that the veloc-ity of 0+ ions measured over the magnetic poles of the planet, which is essentiallytailward with very small y and z-components according to measurements, cannotbe accounted for solely in terms of particle gyromotions. We suggest that the ve-locity of 0+ ions over the magnetic poles of the planet is more probably the resultof wave-particle interactions that mediate the transfer of momentum from the solarwind plasma to ionospheric plasma and newly born ions in the ionosheath.