Ionic loss from Venus upper ionosphere via plasma wake

Recent observations have detected significant escape of ions from the Venusian ionosphere. The measurements indicate that the composition of the escaping mix of ions may reach a critical ratio of H+: O+≈2:1, suggesting that it originated in water molecules, in line with the observed dryness of the planet. In this work, we suggest an additional mechanism that can explain the escape of ions from Venus by invoking a test charge approach. For this purpose, an electrostatic wakefield potential, accompanying a moving test charge, is examined in a plasma consisting of two positive ions (H+ and O+), as well as electrons. It is found that the wakefield potential can be attractive between like charges; it may thus be responsible for gluing charges to an escaping test charge of the same sign, facilitating the collective escape. This attractive potential is strongly influenced by the test charge speed and the plasma density at different altitudes. Our results are consistent with the observation of Venus Express space probe.