The Volcanic Character of Mercury

Mercury is a volcanic world: the planet has experienced a geological history that included partial melting of the interior and the transport of magma to, and eruption onto, the surface. In this chapter, we review Mercury’s volcanic character, first in terms of effusive volcanism (as characterized by lava plains, erosional landforms, and spectral characteristics), next in regard to the planet’s explosive volcanic activity, and then from the perspective of intrusive magmatism. We also visit the planet’s ancient yet spatially expansive intercrater plains and the prospect that they, too, are volcanic. We combine the observations of and inferences for Mercury’s smooth and intercrater plains to propose a model for the planet’s crustal stratigraphy. The extent of our understanding of the petrology of surface materials on Mercury is then discussed, including compositions and lithologies, mineral assemblages, physicochemical properties, and volatile contents. We then describe in broad terms the history of effusive and explosive volcanism on the planet, before addressing the influence that the planet’s lithospheric properties and tectonic evolution have played on volcanism. We finish by listing some major outstanding questions pertaining to the volcanic character of Mercury, and we suggest how those questions might best be addressed.