MESSENGER's exploration of Mercury has revealed a rich and dynamic
geological history and provided constraints on the processes that
control the planet's internal evolution. That history includes
resurfacing by impacts and volcanism prior to the end of the late heavy
bombardment and a subsequent rapid waning of effusive volcanism.
MESSENGER also revealed a global distribution of thrust faults that
collectively accommodated a decrease in Mercury's radius far greater
than thought before the mission. Measurements of elemental abundances on
Mercury's surface indicate the planet is strongly chemically reduced,
helping to characterize the composition and manner of crystallization of
the metallic core. The discovery of a northward offset of the weak,
axially aligned internal magnetic field, and of crustal magnetization in
the planet's ancient crust, places new limits on the history of the core
dynamo and the entire interior. Models of Mercury's thermochemical
evolution subject to these observational constraints indicate that
mantle convection may persist to the present but has been incapable of
significantly homogenizing the mantle. These models also indicate that
Mercury's dynamo generation is influenced by both a static layer at the
top of the core and convective motions within the core driven by
compositional buoyancy.