11:15 AM - 11:30 AM
[PPS04-09] Analysis of the spatial distribution of surface K abundances on Mercury to test thermal redistribution driven by surface-exosphere interaction
★Invited Papers
Keywords:Mercury, Surface composition, Volatile element, Thermal desorption, Gamma-ray spectroscopy
Observations by the MESSENGER spacecraft have revealed that Mercury has the highest volatile element abundance, K/Th ratio, among the inner planets [1,2]. This may reflect the data acquisition concentrated in the northern-high latitudes due to the north-south asymmetric orbit of the MESSENGER spacecraft. Understanding the spatial distribution of the K/Th ratio is important for revealing the representative value of the global surface of Mercury. It has been reported that there is a negative correlation between the K abundances and surface temperatures on Mercury, suggesting that repeated thermal desorption-adsorption processes may produce a spatial distribution that reflects the surface temperature environment [2,3]. The gamma-ray spectroscopic data used in these previous studies were obtained with a large field-of-view and do not accurately reflect the elemental compositions at each location.
This study aimed to clarify the relationship between the K abundances and the surface temperatures. Using a methodology for estimating the elemental compositions corresponding to predefined surface regions from low-spatial resolution data[4], we analyzed gamma-rays spectroscopic data obtained by MESSENGER GRS, combining with the surface temperature model.
To determine the spatial distribution of K and Th abundances on Mercury's surface, this study aims to understand the dominant processes that determine surface composition. We analyzed the gamma-ray spectroscopic data using a methodology for estimating elemental compositions corresponding to defined surface regions from low-spatial resolution data and estimated the surface K and Th abundances corresponding to geological contexts.
Among the smooth plains units with young formation ages, the Northern Plain showed the highest K abundance, while the Caloris Plains showed the lowest K abundance. No significant diversity in Th abundance was found between the smooth plains and intercrater plains with older formation ages. The derived K/Th ratios did not show a correlation with the surface crater densities. On the other hand, a negative correlation between K abundance and surface temperature was observed, which is consistent with the thermal redistribution scenario. This suggests that the spatial distribution of K abundances on the present Mercury surface reflects the surface temperature environment more dominantly than the exogenous contamination. The northern averaged K/Th ratio was estimated to be 4800 ± 600, lower than previous estimates, implying that volatile contents at Mercury's surface, or even in bulk Mercury, may be lower than previously estimated.
[1]Peplowski et al., 2011, Science, 333, 6051, 1850-1852. [2]Peplowski et al., 2012, JGR, 117, E12, 2012JE004141. [3] Hyodo et al., 2021, Icarus, 354, 114064. [4]Peplowski et al., 2014, Icarus, 228, 86-95.
This study aimed to clarify the relationship between the K abundances and the surface temperatures. Using a methodology for estimating the elemental compositions corresponding to predefined surface regions from low-spatial resolution data[4], we analyzed gamma-rays spectroscopic data obtained by MESSENGER GRS, combining with the surface temperature model.
To determine the spatial distribution of K and Th abundances on Mercury's surface, this study aims to understand the dominant processes that determine surface composition. We analyzed the gamma-ray spectroscopic data using a methodology for estimating elemental compositions corresponding to defined surface regions from low-spatial resolution data and estimated the surface K and Th abundances corresponding to geological contexts.
Among the smooth plains units with young formation ages, the Northern Plain showed the highest K abundance, while the Caloris Plains showed the lowest K abundance. No significant diversity in Th abundance was found between the smooth plains and intercrater plains with older formation ages. The derived K/Th ratios did not show a correlation with the surface crater densities. On the other hand, a negative correlation between K abundance and surface temperature was observed, which is consistent with the thermal redistribution scenario. This suggests that the spatial distribution of K abundances on the present Mercury surface reflects the surface temperature environment more dominantly than the exogenous contamination. The northern averaged K/Th ratio was estimated to be 4800 ± 600, lower than previous estimates, implying that volatile contents at Mercury's surface, or even in bulk Mercury, may be lower than previously estimated.
[1]Peplowski et al., 2011, Science, 333, 6051, 1850-1852. [2]Peplowski et al., 2012, JGR, 117, E12, 2012JE004141. [3] Hyodo et al., 2021, Icarus, 354, 114064. [4]Peplowski et al., 2014, Icarus, 228, 86-95.