Recent tectonic activity on Mercury revealed by small thrust fault scarps

Abstract

The planet Mercury has contracted over its history. The identification of small thrust fault scarps suggests the occurrence of tectonic activity on Mercury within the past 50 million years and thus a slow-cooling planetary interior. Large tectonic landforms on the surface of Mercury, consistent with significant contraction of the planet, were revealed by the flybys of Mariner 10 in the mid-1970s1. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission confirmed that the planet’s past 4 billion years of tectonic history have been dominated by contraction expressed by lobate fault scarps that are hundreds of kilometres long2,3,4,5. Here we report the discovery of small thrust fault scarps in images from the low-altitude campaign at the end of the MESSENGER mission that are orders of magnitude smaller than the large-scale lobate scarps. These small scarps have tens of metres of relief, are only kilometres in length and are comparable in scale to small young scarps on the Moon6,7,8. Their small-scale, pristine appearance, crosscutting of impact craters and association with small graben all indicate an age of less than 50 Myr. We propose that these scarps are the smallest members of a continuum in scale of thrust fault scarps on Mercury. The young age of the small scarps, along with evidence for recent activity on large-scale scarps, suggests that Mercury is tectonically active today and implies a prolonged slow cooling of the planet’s interior.