Widespread small grabens consistent with recent tectonism on Mercury

Since Mariner 10 first imaged Mercury in 1974, tectonic landforms dominated by shortening structures have been extensively documented. Contractional tectonism on Mercury is thought to have begun early in the planet's history and is theorized to have continued throughout Mercury's geological history, but observational evidence for recent tectonism is limited. Here we report the widespread occurrence of relatively young grabens on Mercury from global mapping of tectonic features using MESSENGER imagery. The identified grabens are about 10 to 150 m deep, tens of kilometres in length and generally less than 1 km wide. We find that the grabens occur as secondary tectonic features on larger compressional tectonic structures, which indicates continued activity of the parent structure. We estimate that they must be similar to 300 million years old or younger; otherwise, impact gardening would have masked their signature by burial and infilling. The widespread distribution of grabens and their young age supports the continued activity of Mercury's shortening structures into geologically recent times and is consistent with thermochemical evolution models for a slowly cooling planetary interior and prolonged global contraction.