Capture of solar wind alpha-particles by the Martian atmosphere

Integration along He(++) test-particle trajectories in the self-consistent electromagnetic fields generated by three-dimensional hybrid simulations of the solar wind/Mars interaction is used to evaluate the removal of solar wind alpha-particles due to charge-exchange processes with neutral species of the Martian exosphere. The total removal rate of solar wind He(++) ions, transformed into either singly ionised or neutral helium, is equal to 6.7 x 10(23) s(-1), which corresponds approximately to 30% of the flux of solar alpha-particles through the planetary cross-section. The deposition rate of helium neutral atoms, created by double electronic capture on exospheric oxygen, impacting the exobase, and penetrating below where it can be trapped, is about 1.5 x 10(23) s(-1). That means an important contribution of the solar wind source to the helium balance of the Martian atmosphere. The implantation of the solar helium into the Martian atmosphere shows an asymmetry related to the orientation of the motional electric field of the solar wind, -V(SW) x B(IMF). Citation: Chanteur, G. M., E. Dubinin, R. Modolo, and M. Fraenz (2009), Capture of solar wind alpha-particles by the Martian atmosphere, Geophys. Res. Lett., 36, L23105, doi: 10.1029/2009GL040235.