Simulation of Venus Lightning-I: Characterization of Free Radicals Generated in Venus Major Gas Mixture

Abstract

A new Venus-ESD-Chamber (VEC) and peripheral systems were designed and built to simulate Venus lightning. It consists of three subsystems (a) electrostatic discharge (ESD) generation, (b) environmental pressure, temperature, gas composition control & monitoring, and (c) optical and non-optical sensors. We conducted arc discharge experiments in air, in CO2, and in Venus major gas mixture (CO2-N2, 96.5% ± 1.5%:3.5% ± 1.5%) under 10, 350, 700, and 1,000 mbar pressures, that correspond to the 50–75 km altitude range in the cloud layer of Venus. Plasma and Raman spectra, plus gas sensors, and GC-MS were used to identify the ESD products and to semi-quantify CO and O3 generated by ESD. We have found all species of free radicals that have been found in previous simulation studies using different discharge technologies, including some important species in CO2-N2 system, nitrogen oxides and CN. In addition, we found three species (O3, N2+, and C2) that have not been previously reported. Our results suggest that electron flux and kinetic energy are the determining factors for the type of generated free radical species and gas pressure plays a less important role. We found that the quantity of CO changes with the type of ESD. The detection of O3 in this study suggests that lightning might be one of the sources of O3 observed in the Venusian atmosphere. OI emission line at 777.4 nm is the most prominent line in our plasma spectra of FD, consistent with the intense optical flash observed by the Lightning and Airglow Camera (LAC) on the Akatsuki mission.