[P-EM10] Space Weather and Space Climate

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

*Emika Fujii¹, Vladimir Airapetian², Tatsuhiko Sato³, Yosuke Alexandre Yamashiki¹ (1.Graduate School of Advanced Integrated Studies in Human Survivability Kyoto University, 2.National Aeronautics and Space Administration Goddard Space Flight Center, 3.Japan Atomic Energy Agency)

Keywords: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.