Flying just 295km above Mercury’s North Pole ... across the surface during volcanic eruptions, creating these smooth plains.

The last mission to Mercury—three passes by Mariner 10 ... At least 40 percent of the surface consists of smooth plains, most of which are ancient lava flows. When Mariner 10 flew past, it ...

Most of these flooded plains are smooth, with a few impact craters that must have been formed more recently. The Caloris Basin, which at 1500 kilometres wide is Mercury’s largest crater ...

Mercury's magnetic field ... faults cutting across and deforming older craters and relatively young smooth plains, which are interpreted as volcanic flows, have been observed in the Mariner ...