[P-EM10] Space Weather and Space Climate

[PEM10-12] Tracing Evidence of the Young Sun's Magnetic Activity from the Lunar South Pole Regolith

*藤井 咲花¹、Vladimir Airapetian²、佐藤 達彦³、山敷 庸亮¹ (1.京都大学大学院総合生存学館、2.National Aeronautics and Space Administration Goddard Space Flight Center、3.国立研究開発法人日本原子力研究開発機構)

キーワード：Lunar regolith、Young Sun、isotope、flares

Observations of young Sun's analogues and theoretical models of solar and stellar activity suggest that the young Sun was a frequent and powerful source of superflares that affected objects in the solar system during its first 200 million years. We propose that the Moon’s South Pole is an ideal region to study the effects of the young Sun's magnetic activity. This is because the ice and regolith in permanently shadowed regions may preserve traces of interaction of high-energy (with energies exceeding 10 GeV) solar particles with the lunar surface. Apollo lunar samples suggest that the early Moon was a magnetized body with a relatively strong global magnetic field formed over 4.2 billion years ago. This, high-energy protons and heavy ions associated with solar superflares are thought to had deflected from equatorial regions and predominantly impacted the lunar polar regions, inducing changes in stable isotope ratios—such as 28Si/29Si or 15N/14N—through spallation reactions. Here, we present preliminary results from calculations performed using the Particle and Heavy Ion Transport code System (PHITS) to assess the production rates of cosmogenic isotopes resulting from interactions with early lunar regolith and ice. Our findings indicate that the observed changes in the isotopic ratios of hydrogen, neon, and nitrogen, which are to be searched for in future missions, can provideevidence of the impact of the young Sun's frequent superflares.