[P-PS07] Planetary Sciences

[PPS07-09] The relation between the surface composition anomaly and the distribution of the exosphere of Mercury

*Yudai Suzuki¹, Kazuo Yoshioka¹, Go Murakami², Ichiro Yoshikawa¹ (1.University of Tokyo, 2.JAXA/ISAS)

Keywords:Mercury, BepiColombo mission, Mio spacecraft, exosphere

In celestial bodies with collisionless atmospheres, such as Mercury, the spatial distribution of the exosphere is expected to reflect the surface composition. In this study, we discuss whether the distribution of Mg, Ca, and Na, the primary exospheric components on Mercury, have exosphere-surface correlation by analyzing the observation data of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) and X-Ray Spectrometer (XRS) onboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. As a result, it was found that Mg has strong exosphere-surface correlation, which is consistent with the previous study (Merkel et al., 2018), Ca has weak correlation and Na has little correlation. The Monte Carlo simulations of trajectories in the exosphere show that the weak correlation of Ca is due to the relatively large solar radiation acceleration. For Na, fluctuations in production rate other than seasonal variations were detected only in the high temperature regions around 0°E and 180°E.. This can be explained well by considering that the weakly physisorbed Na layer on the surface is depleted under high temperature and that the distribution of strongly chemisorbed Na atoms is reflected in the exosphere. Based on these results, the conditions for components with correlation in celestial bodies with thin atmospheres include low volatility and little solar radiation acceleration.