CONTEXT: The complex interplay between the Solar Wind and the lunar surface serves as a quintessential example of space weathering. However, uncertainties persist regarding the influence of plasma originating from Earth’s ionosphere, necessitating a comprehensive understanding of its quantitative impact. Hitherto, the dearth of reliable models has impeded accurate computation of ion flux from Earth to the Moon under varying solar wind conditions. AIM: The objective of this study is to adapt a kinetic model for the challenging conditions of having both the Earth and the Moon in a single simulation box. METHODS: IAPIC, the Particle-In-Cell Electromagnetic Relativistic Global Model was modified to handle the Sun-Earth-Moon system. It employs kinetic simulation techniques that have proven invaluable tools for exploring the intricate dynamics of physical systems across various scales while minimizing the loss of crucial physics information such as backscattering. RESULTS: The modeling allowed to derive the shape and size of the Earth’s magnetosphere and allowed tracking the O+ and H+ ions escaping from the ionosphere to the Moon: O+ tends to escape towards the dayside magnetopause, while H+ travels deeper into the magnetotail, extending up to the Lunar surface. In addition, plasma temperature anisotropy and backstreaming ions were simulated, allowing for future comparison with the experiment. CONCLUSION: This study shows how a kinetic model can successfully be applied to study the transport of ions in the Earth-Moon environment. A second paper will detail the effect on the Lunar environment and the impact on the Lunar water.

The boundary between the solar wind (SW) and the Earths magnetosphere, the magnetopause (MP), is highly dynamic. Its location and shape depend on SW dynamic pressure and interplanetary magnetic field (IMF) orientation. We use a 3D kinetic Particle-In-Cell code (IAPIC) to simulate an event observed by THEMIS spacecraft on July 16, 2007. We investigate the impact of radial (θBx=0◦) and non-radial (θBx=50◦) IMF on the shape and size of Earths MP for a dipole tilt of 31◦ using maximum density gradient and pressure balance methods. Using the Shue model as a reference (MP at 10.3 RE), we find that for non-radial IMF the MP expands by 1.4 and 1.7RE along the the Sun-Earth (OX) and tilted magnetic equatorial (Tilt) axes, respectively, and it expands by 0.5 and 1.6RE for radial IMF along the same respective axes. When the effect of backstreaming ions is removed from the bulk flow, the expansion ranges are 1.0 and 1.3RE and 0.2, and 1.2RE, respectively. It is found that the percentage of backstreaming to bulk flow ions are 16.5% and 20% for radial and non-radial IMF. We also show that when the backstreaming ions are not identified, up to 40% of the observed expansion that is due to backstreaming particles can be inadvertently attributed to a change in the SW upstream properties. Finally, we quantified the temperature anisotropy in the magnetosheath, and observe a strong dawn-dusk asymmetry in the MP location, being more extended on the duskside than on the dawnside.

The boundary between the solar wind (SW) and the Earth’s magnetosphere, named the magnetopause (MP), is highly dynamic. Its location and shape can vary as a function of different SW parameters such as density, velocity, and interplanetary magnetic field (IMF) orientations. In the present paper an event of July 26, 2017, captured by THEMIS spacecraft is simulated by a 3D kinetic Particle-In-Cell (IAPIC) code. We investigate the impact of radial (B = Bx) and quasi-radial (Bz < Bx,By) IMF on the shape and size of Earth’s MP for a dipole tilt of 31◦ using both maximum density steepening and pressure system balance methods for identifying the boundary. We found that, compared with northward or southward-dominant IMF conditions, the MP position expands asymmetrically by 8 to 22\% under radial IMF. In addition, we construct the MP shape along the tilted magnetic equator and the OX axes showing that the expansion is asymmetric, not global, stronger on the MP flanks, and is sensitive to the ambient IMF. Finally, we investigate the contribution of SW ions back-scattered by the bow shock to the MP expansion, the temperature anisotropy in the magnetosheath, and a strong dawn-dusk asymmetry in MP location. These simulations can substantially contribute in a complementary manner with the available MHD and Hybrid models to both future space mission measurements and exoplanet magnetosphere investigations.