Widely different characteristics of oxygen and hydrogen ion escape from Venus

Abstract

We study the solar wind induced escape of O + and H + ions from Venus' atmosphere in the HYB-Venus hybrid simulation. Most of the previous Venus global plasma modelling studies have concentrated only on the O + escape. According to the hybrid simulation, planetary O + and H + ions behave very differently from each other in the Venusian induced magnetosphere. Both species are asymmetrically distributed in the direction of the interplanetary electric field and in the dawn-dusk plane. The H + flow can be understood by E × B drift motion but finite Larmor radius (FLR) effects are essential to the behavior of O + ions. These differences result in different H + /O + escape ratios globally and in the plasma wake. Further, the energy ratio of the escaping planetary ions was found to be consistent with the observations made in the near Venus wake by the ASPERA-4 instrument onboard the Venus Express spacecraft. © 2010 by the American Geophysical Union.