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

Abstract

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, https://doi.org/10.1002/2016GL068327) 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 ± 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.

Superthermal Electron Observations at Mars During the December 2022 Disappearing Solar Wind Event

“…The inferred ambipolar potential at Mars with this method is around 0.7 V on the dayside and up to 1.5 V in the tail, similar to previous results (Akbari et al, 2019). At Venus, the inferred potential is much larger, up to 10 V, by Collinson et al (2016), but a follow-up study by Collinson et al (2023) concludes that these large potentials are likely atypical and extreme outliers associated with a transient phenomenon in the Venusian ionosphere. It is also worth mentioning that the ambipolar potential and electric field are derived within the Mars magnetosphere by Xu, Mitchell, et al (2021), mainly resulting from the electron pressure gradient between the hot sheath flow and the cold planetary flow.…”

“…The ambipolar electric field and the associated ambipolar potential ( U A ) have been derived from the measured thermal (<1 eV) electron density and temperature for Mars (Akbari et al., 2019; Ergun et al., 2016) and Venus (Collinson et al., 2016), with a magnitude of order | E A |∼ 0.1 − 1 mV/km and U A ∼ − 1 V (relative to the ionospheric production region) at both planets. Alternatively, the ambipolar potential has been derived from the energy shift of the He‐II peak in the ionospheric photoelectron energy spectrum at Mars (Xu, Mitchell, et al., 2018) and Venus (Collinson et al., 2016, 2023). As the He‐II peak is produced by the 30.4 nm solar He‐II emission line, the corresponding flux peak in the photoelectron energy spectrum is fixed at 23–37 eV (the excessive photon energy above the photoionization potential) at production and can be shifted to different energies by ambient plasma potentials.…”

“…(2016), but a follow‐up study by Collinson et al. (2023) concludes that these large potentials are likely atypical and extreme outliers associated with a transient phenomenon in the Venusian ionosphere. It is also worth mentioning that the ambipolar potential and electric field are derived within the Mars magnetosphere by Xu, Mitchell, et al.…”