Mercury's global contraction much greater than earlier estimates

Mercury, a planet with a lithosphere that forms a single tectonic plate, is replete with tectonic structures interpreted to be the result of planetary cooling and contraction. However, the amount of global contraction inferred from spacecraft images has been far lower than that predicted by models of the thermal evolution of the planets interior. Here we present a synthesis of the global contraction of Mercury from orbital observations acquired by the MESSENGER spacecraft. We show that Mercurys global contraction has been accommodated by a substantially greater number and variety of structures than previously recognized, including long belts of ridges and scarps where the crust has been folded and faulted. The tectonic features on Mercury are consistent with models for large-scale deformation proposed for a globally contracting Earthnow obsoletethat pre-date plate tectonics theory. We find that Mercury has contracted radially by as much as 7 km, well in excess of the 0.83 km previously reported from photogeology and resolving the discrepancy with thermal models. Our findings provide a key constraint for studies of Mercurys thermal history, bulk silicate abundances of heat-producing elements, mantle convection and the structure of its large metallic core.