9:30 AM - 9:45 AM
[PPS08-13] 4He and 20Ne from Coronal Mass Ejection Recorded in Ilmenite Grain from Lunar Soil 71501
Keywords:Lunar regolith, Solar wind, Coronal mass ejection
Introduction: Solar-type stars are known to be active in their early stages of formation [e.g., 1]. On the other hand, it is not well understood how the Sun has evolved in the past. In this study, we focus on the past energy of the solar wind. The Sun emits plasma into interplanetary space as solar wind and coronal mass ejections (CMEs). When these plasmas reach to an airless celestial bodies such as lunar surface, they are implanted into the lunar regolith materials. The implantation range increases with increasing the particle speed. Therefore, we can estimate an energy distribution of the implanted particles by depth profiling of the solar wind components [2].
Samples and Methods: We used two ilmenite grains from Apollo 17 lunar soil 71501 (71501#1 and 71501#3). Soil 71501 is estimated to have been exposed to solar wind of ~100 Myr ago [3, 4].
Noble gas analysis was performed using laser ionization mass nanoscope (LIMAS) [e.g., 2, 5]. Depth profiling was performed by the same procedure as in [2]. We measured 4He+, 20Ne+, and the major element ions of ilmenite, 56Fe2+, 48Ti4+, and 16O2+. A polished terrestrial ilmenite implanted with 4He (3 × 1015 cm-2, 20 keV) and 20Ne (1 × 1014 cm-2, 100 keV) was used as a standard to calibrate the concentrations of samples.
The solar wind energy distribution [6] observed by the ACE/SWICS for the 2.3-year period 2001–2004 and fluences of 4He and 20Ne obtained from Genesis target material at the same period [7] were used to analyze the noble gas depth profiles. We also used SRIM [8] to simulate ion implantation. We used the energy distribution of [6] slower than 900 km/s as an index of 2.3 years average solar wind, and that faster than 900 km/s as an index of CMEs associated with Halloween solar storms (Halloween-CME; H-CME). SRIM simulations were performed for each index to estimate the depth profiles formed by the average solar wind for 2.3 years and by a single H-CME class energetic particles.
Results and Discussion: Depth distributions of noble gases show peaks in depth of ~15–30 nm from the surface of both grains. This peak depth was comparable with the depth distribution of average solar wind. Peak concentrations of 20Ne were 2 × 1019 and 6 × 1019 cm-3 for 71501#1 and 71501#3, respectively. From these concentrations, solar wind exposure ages were estimated to be 1200 and 3000 years, respectively.
The gentle slope of the depth profiles deeper than 100 nm may be derived from H-CME class energetic particles. The estimated depth profile of H-CME was compared with the profiles obtained from lunar samples. The results show that 71501#1 and 71501#3 show distributions comparable with 170 and 1000 times accumulation of H-CME class energetic particles, respectively.
Based on these results, we estimated the frequency of H-CME class energetic events on the Sun 100 million years ago. The frequencies obtained from 71501#1 and 71501#3 were 15 and 30 times per 100 years, respectively. On the present Sun, Halloween solar storm class CMEs occur about 10 times per 100 years [8]. It is possible that the Sun at 100 Myr ago was more violent than the present.
References: [1] Feigelson E. D. et al. (2002) ApJ. 572, 335–349. [2] Bajo K. et al. (2015) Geochem. J. 49, 559–566. [3] Benkert J. -P. et al. (1993) J. Geophys. Res. 98, 13147–13162. [4] Eugster O. et al. (2001) Meteorit. Planet. Sci. 36, 1097–1115. [5] Yurimoto H. et al. (2016) Surf. and Interf. Anal. 48, 1181–1184. [6] Reisenfeld D. B. et al. (2013) Space Sci. Rev. 175, 125–164. [7] Ziegler J. F. et al. (2010). Nucl. Instrum. Methods Phys. Res. B. 268, 1818–1823. [8] Gopalswamy N. (2018) In Extreme Events in Geospace, 37–63.
Samples and Methods: We used two ilmenite grains from Apollo 17 lunar soil 71501 (71501#1 and 71501#3). Soil 71501 is estimated to have been exposed to solar wind of ~100 Myr ago [3, 4].
Noble gas analysis was performed using laser ionization mass nanoscope (LIMAS) [e.g., 2, 5]. Depth profiling was performed by the same procedure as in [2]. We measured 4He+, 20Ne+, and the major element ions of ilmenite, 56Fe2+, 48Ti4+, and 16O2+. A polished terrestrial ilmenite implanted with 4He (3 × 1015 cm-2, 20 keV) and 20Ne (1 × 1014 cm-2, 100 keV) was used as a standard to calibrate the concentrations of samples.
The solar wind energy distribution [6] observed by the ACE/SWICS for the 2.3-year period 2001–2004 and fluences of 4He and 20Ne obtained from Genesis target material at the same period [7] were used to analyze the noble gas depth profiles. We also used SRIM [8] to simulate ion implantation. We used the energy distribution of [6] slower than 900 km/s as an index of 2.3 years average solar wind, and that faster than 900 km/s as an index of CMEs associated with Halloween solar storms (Halloween-CME; H-CME). SRIM simulations were performed for each index to estimate the depth profiles formed by the average solar wind for 2.3 years and by a single H-CME class energetic particles.
Results and Discussion: Depth distributions of noble gases show peaks in depth of ~15–30 nm from the surface of both grains. This peak depth was comparable with the depth distribution of average solar wind. Peak concentrations of 20Ne were 2 × 1019 and 6 × 1019 cm-3 for 71501#1 and 71501#3, respectively. From these concentrations, solar wind exposure ages were estimated to be 1200 and 3000 years, respectively.
The gentle slope of the depth profiles deeper than 100 nm may be derived from H-CME class energetic particles. The estimated depth profile of H-CME was compared with the profiles obtained from lunar samples. The results show that 71501#1 and 71501#3 show distributions comparable with 170 and 1000 times accumulation of H-CME class energetic particles, respectively.
Based on these results, we estimated the frequency of H-CME class energetic events on the Sun 100 million years ago. The frequencies obtained from 71501#1 and 71501#3 were 15 and 30 times per 100 years, respectively. On the present Sun, Halloween solar storm class CMEs occur about 10 times per 100 years [8]. It is possible that the Sun at 100 Myr ago was more violent than the present.
References: [1] Feigelson E. D. et al. (2002) ApJ. 572, 335–349. [2] Bajo K. et al. (2015) Geochem. J. 49, 559–566. [3] Benkert J. -P. et al. (1993) J. Geophys. Res. 98, 13147–13162. [4] Eugster O. et al. (2001) Meteorit. Planet. Sci. 36, 1097–1115. [5] Yurimoto H. et al. (2016) Surf. and Interf. Anal. 48, 1181–1184. [6] Reisenfeld D. B. et al. (2013) Space Sci. Rev. 175, 125–164. [7] Ziegler J. F. et al. (2010). Nucl. Instrum. Methods Phys. Res. B. 268, 1818–1823. [8] Gopalswamy N. (2018) In Extreme Events in Geospace, 37–63.