17:15 〜 19:15
[PCG19-P05] Observational study of the impact of solar energetic particles on the Martian ozone layer
Ozone is a critical trace gas for understanding the dynamics and photochemistry of planetary atmospheres. It also plays a crucial role in protecting life from exposure to severe ultraviolet solar radiation. On Earth, it is well known that ozone is efficiently destroyed by odd nitrogen (NOx) and odd hydrogen (HOx) generated by solar energetic particles (SEPs) penetrating into the atmosphere. However, SEP-induced impact on the atmospheric composition has not been identified on planets other than Earth, such as Mars, which lacks a global magnetic field and has a thin CO2-dominated atmosphere. Mars has a particularly harsh environment to SEP events, as demonstrated by the recent discovery of global diffuse aurorae (Schneider et al., 2015). Nakamura et al. (2023) predicted that such a space-atmosphere interaction induced by SEP would cause significant impacts on Mars' atmospheric composition. Herein, we report unique ozone observations by NOMAD/UVIS during the SEP event.
We analyzed the retrieved ozone column density acquired by the spectra in the ultraviolet to visible (UVIS) channel of the NOMAD (Nadir and Occultation for MArs Discovery) instrument onboard the ExoMars Trace Gas Orbiter (TGO). We confined our analysis to the major SEP event in February 2024.
We found that the retrieved ozone column during this event exhibited a gradual seasonal increase consistent with previous studies. Meanwhile, a relative decrease of ~15% was identified during the peak phase of the SEP event. The further analysis is required to have a confidence the SEP-induced variation by comparing the computer simulations and observations in other Martian Years. Based on observed SEP spectra by the SEP instrument onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, our model predicted that the SEP energy up to 1 MeV was sufficient to penetrate the Martian atmosphere down to ~50 km and cause the remarkable depletion of ozone column density ~7%. Our model suggests water cluster ions (H+(H2O)n) generated by SEP produce HOx compounds that destroy ozone in the CO2-dominated atmosphere. In this study, we will report further investigation to determine whether this ozone reduction is caused by the SEP or by other factors such as atmospheric circulation or cloud effects. This study will provide the potential observational indication of SEP-induced changes in the Martian atmospheric composition. Understanding the impact of SEP on Mars is crucial for reconstructing the planet's atmospheric evolution from its early epoch, when solar activity was more intense than today, to its current state.
We analyzed the retrieved ozone column density acquired by the spectra in the ultraviolet to visible (UVIS) channel of the NOMAD (Nadir and Occultation for MArs Discovery) instrument onboard the ExoMars Trace Gas Orbiter (TGO). We confined our analysis to the major SEP event in February 2024.
We found that the retrieved ozone column during this event exhibited a gradual seasonal increase consistent with previous studies. Meanwhile, a relative decrease of ~15% was identified during the peak phase of the SEP event. The further analysis is required to have a confidence the SEP-induced variation by comparing the computer simulations and observations in other Martian Years. Based on observed SEP spectra by the SEP instrument onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, our model predicted that the SEP energy up to 1 MeV was sufficient to penetrate the Martian atmosphere down to ~50 km and cause the remarkable depletion of ozone column density ~7%. Our model suggests water cluster ions (H+(H2O)n) generated by SEP produce HOx compounds that destroy ozone in the CO2-dominated atmosphere. In this study, we will report further investigation to determine whether this ozone reduction is caused by the SEP or by other factors such as atmospheric circulation or cloud effects. This study will provide the potential observational indication of SEP-induced changes in the Martian atmospheric composition. Understanding the impact of SEP on Mars is crucial for reconstructing the planet's atmospheric evolution from its early epoch, when solar activity was more intense than today, to its current state.