[P-CG19] 惑星大気圏・電磁圏

[PCG19-P06] Simulation of Oxygen Green Aurora Emission on Venus

*Pucheng Lu¹、Yuki Nakamura¹、Candace Gray³、Keshav R. Tripathi²、Takeshi Imamura²、Lauriane Soret⁴、Jean-Claude Gérard⁴、Hiromu Nakagawa⁵、Shohei Aoki²、Kanako Seki¹、Naoki Terada⁵、Yuki Harada⁶、Nicholas M. Schneider⁷、Francois Leblanc⁸、Beatriz Sánchez-Cano⁹ (1.Department of Earth and Planetary Science, Graduate School of Science, the University of Tokyo、2.Department of Complexity Science and Engineering, Graduate School of Frontier Science, the University of Tokyo、3.Department of Astronomy - Apache Point Observatory, New Mexico State University、4.Space sciences, Technologies and Astrophysics Research Institute, University of Liège、5.Graduate School of Science, Tohoku University、6.Department of Geophysics, Graduate School of Science, Kyoto University、7.Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder、8.LATMOS/CNRS, Sorbonne Université、9.School of Physics and Astronomy, University of Leicester)

キーワード：Solar energetic particles, Venusian aurorae, Monte Carlo simulation, Electron density

Aurora is a luminous event generated by energetic particles interacting with planetary atmospheres. Recent observations by Mars Express, Mars Atmosphere and Volatile Evolution (MAVEN), and Emirates Mars Mission (EMM) missions revealed a variety of aurorae on the nightside of Mars with different sources. Discrete and sinuous aurorae are localized emissions caused by the suprathermal electrons energized in the magnetosheath or the magnetotail (Bertaux et al., 2005; Lillis et al., 2022). In contrast, global diffuse aurora spans across the nightside of Mars due to the precipitation of 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) (Schneider et al., 2015). Since Mars lacks a global intrinsic magnetic field, SEPs can access the Martian atmosphere globally on the nightside. Due to the similar magnetic field configuration, Venus is expected to have a global diffuse aurora during SEP events. The ground-based observation by Apache Point Observatory (APO) 3.5 m telescope, the atomic oxygen auroral missions at 557.7 nm has been discovered in association with the arrival of CMEs and CIRs, suggesting that they are driven by SEP proton precipitation (Gray et al., 2025). 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 the Oct. 27^th, 2013 event and 1×10⁵ cm^-3 for the Jul. 14^th, 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 altitudes 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.