Simulation of Oxygen Green Aurora Emission on Venus

Aurora is a luminous event generated by energetic particles interacting with the atmosphere on different planets. As for the solar system planets having no strong intrinsic magnetic field, the primary sources of energetic particles are solar energetic particles (SEPs) accelerated by magnetic reconnection in solar flares and by shock waves driven by coronal mass ejections (CMEs) and corotating interaction regions (CIRs). As observed by Apache Point Observatory (APO), the Venusian aurorae usually happened after the SEPs events passage. However, it is still unclear whether the origin of the aurorae is SEPs or not. Here we used a Monte Carlo model PTRIP (Nakamura et al., 2022) to simulate the ionization rate and emission rate of the atomic oxygen green line. We found that the simulated electron densities are consistent with the radio occultation measurements VeRa on board Venus Express (VEx) in terms of both peak altitude and density. Our estimations of the electron densities are 2×104 cm-3 for Oct. 27th, 2013 event and 1×105 cm-3 for Jul. 14th, 2012 event, while the peak altitudes are 113 km and 106 km respectively. It is very comparable with the measurements of VeRa/VEx, the electron densities are 2×104 cm-3 and 0.5×105 cm-3, while the peak altitude are around 120 km and 113 km, respectively. The brightness of the 557.7 nm emission is on the order of 10-100 R in the nadir and 1-10 kR in the limb, which is bright enough to be detected using ground-based telescopes. Our work is the first theoretical study to evaluate the production of 557.7 nm aurorae on Venus. The results support that the 557.7 nm Venusian aurorae are generated by SEPs precipitation. Our work provides a reference for future observation of the Venusian aurora.