[P-PS09] Lunar Science and Exploration

[PPS09-13] Comprehensive characterization of charged particles and electromagnetic fields in the lunar mini-magnetosphere based on low-altitude data obtained by Kaguya

*Kohei Ogino¹, Yuki Harada¹, Masaki N Nishino², Yoshifumi Saito², Shoichiro Yokota³, Yoshiya Kasahara⁴, Atsushi Kumamoto⁵, Futoshi Takahashi⁶, Hisayoshi Shimizu⁷ (1.Graduate School of Science, Kyoto University, 2.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3.Graduate School of Science, Osaka University, 4.Information Media Center, Kanazawa University, 5.Graduate School of Science, Tohoku University, 6.Department of Earth and Planetary Sciences, Kyushu University, 7.Earthquake Research Institute, University of Tokyo)

Keywords:Moon, Plasma, Electromagnetic field, Mini-magnetosphere, Kaguya

Although the Moon does not have a global magnetic field like the Earth, crustal remanent magnetizations (lunar magnetic anomalies, hereafter LMAs) are nonuniformly distributed over the lunar surface. The interaction between the solar wind and LMAs leads to the formation of mini-magnetospheres. Since the spatial scales of lunar mini-magnetospheres are very small, typically below several tens of kilometers, direct observations of the lunar mini-magnetospheres are challenging from a typical altitude of lunar orbiters (~100 km). As a result, the plasma environment and electromagnetic field structure in the solar wind-LMA interaction region have not been fully understood. Saito et al. (2012) first reported simultaneous observations of ions and electrons below 30 km altitude based on a single low-altitude path obtained by ‘Kaguya’. In this study, we extensively analyze low-altitude data of ions, electrons, magnetic fields (1-10 Hz), and wave electric fields (1-10 kHz) obtained by Kaguya. By analyzing multiple orbits over various LMAs, we aim to comprehensively characterize the plasma environment and electromagnetic fields in the solar wind-LMA interaction region. We find that, at any LMAs, the acceleration of the incident solar wind electrons and deceleration of the solar wind ions are consistently observed in the region where the model crustal magnetic field (Tsunakawa et al., 2015) is stronger than 4 nT, suggesting the existence of anti-moonward electrostatic fields in these regions. By analyzing the characteristics of particles and electromagnetic fields inside the region as well as the outside, it has been shown that upward electrostatic fields are closely related to solar wind ion reflection and strong plasma wave excitation. This suggests that the upward electrostatic fields at low altitudes play important roles in many kinds of phenomena associated with solar wind-LMA interaction. Based on the result derived from the currently available low-altitude data, we discuss implications for future low-orbiting or lander missions.