Global MHD simulations of Mercury's interaction with the solar wind: Influence of the planetary conducting core on the magnetospheric interaction

Mercury's comparatively weak intrinsic magnetic field and its close proximity to the Sun lead to a mini-magnetosphere that undergoes more direct space-weathering interactions than other planets. A unique aspect of the Mercury interaction system relates to the large ratio of the scale of the planet to the scale of the tiny magnetosphere and the presence of a large-size core (with radius ~ 80% of the planetary radius) composed of highly conducting material, implying that there is potentially strong feedback between the planet's interior and the magnetosphere, especially under conditions of strong solar wind driving. Understanding the solar wind-magnetosphere-exosphere-interior interaction at Mercury as a highly coupled system requires not only analysis of spacecraft data but also a modeling framework that is both comprehensive and inclusive. To this end, we have developed a new global MHD model of Mercury's interaction with the solar wind based on the BATSRUS code in which the interior of the planet (modeled as layers of different electric conductivities) is electrodynamically coupled to the surrounding space plasma environment. The new modeling capability allows for self-consistently characterizing the dynamical response of the Mercury system to time-varying external conditions. In particular, we have applied the coupled model to assess quantitatively the effect of induction arising from the planet's conducting core on the global magnetosphere. A set of idealized simulations have been carried out in which Mercury's magnetosphere is impacted by solar wind disturbances with different levels of pressure enhancement. Our results show that due to the induction effect, Mercury's core can impose strong global influences on the way Mercury responds to changes in the external environment, including modifying the global magnetospheric structure and affecting the extent to which the solar wind directly impacts the planetary surface. By applying the model to simulate extreme events, such as those observed by MESSENGER during impact of Coronal Mass Ejections (Slavin et al., 2013), we aim to obtain a deeper understanding of the tightly coupled Mercury system, and thereby to develop further constraints on the properties of the planet's interior.