  For the first time, we explore the tightly coupled interior-magnetosphere
system of Mercury by employing a three-dimensional ten-moment multifluid model.
This novel fluid model incorporates the non-ideal effects including the Hall
effect, inertia, and tensorial pressures that are critical for collisionless
magnetic reconnection; therefore, it is particularly well suited for
investigating $collisionless$ magnetic reconnection in Mercury's magnetotail
and at the planet's magnetopause. The model is able to reproduce the observed
magnetic field vectors, field-aligned currents, and cross-tail current sheet
asymmetry (beyond the MHD approach) and the simulation results are in good
agreement with spacecraft observations. We also study the magnetospheric
response of Mercury to a hypothetical extreme event with an enhanced solar wind
dynamic pressure, which demonstrates the significance of induction effects
resulting from the electromagnetically-coupled interior. More interestingly,
plasmoids (or flux ropes) are formed in Mercury's magnetotail during the event,
indicating the highly dynamic nature of Mercury's magnetosphere.
