The Influence of a Conductive Core in Magnetosphere Topology and Surface Precipitation on Mercury Under Extreme Solar Wind Conditions

Mercury is the smallest planet in the solar system with a radius of R_M=2440 km and a large conductive core of approximate radius R_C=0.8 R_M [1, 2]. Despite its small stature, Mercury possesses a dynamo generating a dipole-like field with a magnetic moment of 195±10 nT-R_M³ that is offset ~0.2 R_M north [3, 4]. The combination of variable solar wind dynamic pressure due to Mercury's eccentric orbit and the planet’s occupancy of a large fraction of its asymmetric, weak magnetosphere produces a system in which magnetosphere topology and particle precipitation onto the surface are sensitive to both external driving and internal magnetic structure [7, 8, 9, 10]. The Hermean magnetosphere is also influenced by electromagnetic induction due to the presence of Mercury’s electrically conducting core, which modifies the magnetic response due to time-variable external forcing [10, 11, 12]. Previous work has shown that induced currents can strengthen the effective field during solar-wind pressure enhancements, altering magnetopause stand-off distance and compression of the dayside magnetosphere [11, 13, 14, 15, 16].  

We use the Amitis GPU-based hybrid code [17, 18] to investigate the influence of a conductive core on magnetosphere topology and surface precipitation during an extreme solar event under different interplanetary magnetic field (IMF) orientations and interior configurations. We find that across all simulated cases, IMF orientation is the dominant first-order control on where reconnection can occur and on the large-scale reorganization of precipitation patterns, which agrees with previous work [18, 19, 20, 21, 22, 23, 24]. However, the presence of a conductive core modifies the system’s response relative to a purely resistive body, and this modification is most apparent when examining magnetopause boundary motion and precipitation patterns as a function of time. 

References: [1] Smith et al. (2012) Science, [2]  Hauck et al. (2013) JGR: Planets, [3] Anderson et al. (2011) Science, [4] Johnson et al. (2012) JGR: Planets, [5] He et al. (2017) JGR: Space Physics, [6] Korth et al. (2017) GRL, [7] Nevsky et al. (2024) Universe, [8] Slavin et al. (2009) Science, [9] Glassmeier et al. (2007) SSR, [10] Johnson et al. (2016) GRL, [11] Katsura et al. (2021) Icarus, [12] Jia et al. (2015) JGR: Space Physics, [13] Grosser et al. (2004) PSS, [14] Heyner et al. (2016) JGR: Space Physics, [15] Shi et al. (2025) Icarus, [16] Fatemi et al. (2017) J. Phys.: Conf. Ser., [17] Fatemi et al. (2018) A&A,  [18] Slavin et al. (2014) JGR: Space Physics, [19] Fatemi et al. (2020) JGR: Space Physics, [20] Varela et al. (2015) PSS, [21] Exner et al. (2024) JGR: Space Physics, [22] Jia et al. (2019) JGR: Space Physics, [23] Guo et al. (2023) JGR: Planets, [24] Glebe et al. (2026) JGR: Space Physics.