Endogenic origin of the Martian hemispheric dichotomy

Abstract The hemispheric dichotomy is the oldest and largest geologic feature on Mars. The dichotomy refers to the striking elevation difference between the northern and southern hemispheres; 5 km on average. The transition is gradual in places and elsewhere is marked by a sharp boundary. Much of the northern hemisphere is low in elevation and relatively smooth. The remainder of the north and the entire south constitutes the heavily cratered highlands. There is no consensus as to the origin of the dichotomy, but formation hypotheses fall into two broad categories: exogenic (impact-related), and endogenic. In this chapter, we focus on the endogenic origin mechanisms, including long-lived single-plume mantle convection, an early episode of plate tectonics, and long-wavelength overturn of a solidified global magma ocean, as well as hybrid formation methods such as impact-induced mantle convection. Finally, we discuss implications for the present orientation of the dichotomy and its relationship to Tharsis.