A Survey of Strong Electric Potential Drops in the Ionosphere of Venus

Every planet or moon with an ionosphere is thought to generate a weak electrical potential which helps ions overcome gravity and escape to space. A pilot study at Venus by Collinson et al. (2016, ) indicated a planetary potential an order of magnitude stronger than expected. Here we present a statistical study of the electrical potential drop in the ionosphere of Venus, which was found to be an average of 7.04 & PLUSMN; 2.19 V. However, these strong potentials measured by Venus Express are likely atypical and extreme outliers associated with a transient phenomenon in the Venusian ionosphere. We posit they are associated with transient and sporadic density cavities in the ionosphere and may be the result of sporadic electrostatic double layer formation in the dayside ionosphere. Previous investigations have suggested that Venus has a much stronger electrical potential in its ionosphere than expected. This electrical potential is important as it helps charged particles escape into space. At Venus, the potential can be strong enough to directly propel all water-group ions (including oxygen) to escape velocity. Thus, understanding what is responsible for such a strong potential at a planet so similar to Earth is of utmost importance for understanding what makes terrestrial planets habitable. We present a statistical study of all measurements by the European Space Agency's Venus Express Orbiter (2006-2014). This statistical study revealed an average potential of 7.04 & PLUSMN; 2.19 V, far exceeding that at Mars and Earth. However, this measurement was only possible during 30 out of 3,189 orbits of Venus Express. The measurements could only be made at solar minimum and the reasons for this are yet unknown. More research is needed to investigate what generates this strong electric field. To accomplish this, future missions to Venus are necessary with a more comprehensive instrument suite that can measure the planet's electrical potential more consistently. We present a statistical survey of all Venus Express measurements of the electrical potential drop in the Venusian ionosphereMean potential was 7.04 & PLUSMN; 2.2 V, but such strong potentials are likely due to transient and local phenomena possibly electrostatic double layersFuture missions to Venus are necessary to consistently measure its intrinsic electrical field and investigate its typical strengths