A comparison of inner Solar System volcanism

Volcanic and tectonic global maps of the inner planets and the Moon allow conclusions about the long-term volcanic behaviour of terrestrial planets and hint at the most promising extrasolar planets to look for active, radiogenically driven volcanism. The volcanic landforms, eruptive sites and longevity of activity on Mercury and the Moon contrast substantially with those of Earth, Venus and Mars. Here, I synthesize global maps of volcanic and tectonic features for these five worlds and, from the collective records of volcanic activity in the inner Solar System, draw conclusions about the long-term behaviour of terrestrial planets in general. Mercury and the Moon differ from the larger planetary bodies in terms of not only size and composition (and so shorter periods of melt production) but also by their being affected by a horizontally compressive stress state arising from a reduction in planetary volume as they cooled. The phenomenon of global contraction also readily accounts for the dearth of widespread extensional tectonic structures on Mercury and the Moon. From this comparative analysis, the most promising extrasolar planets on which to focus future searches for evidence of active, radiogenically driven volcanism are probably the larger rocky bodies in a mature planetary system or those worlds in relatively young systems.