Pattern of lobate scarps on Mercury’s surface reproduced by a model of mantle convection

Abstract

Numerical simulations suggest that lobate scarps on the surface of Mercury could have resulted from compressive stresses induced by convection within the planet’s mantle, in addition to those generated by global contraction. Mercury is the smallest and least tectonically active of the terrestrial planets1,2. Although Mercury’s ancient, cratered surface resembles the Moon, it has the largest ratio of metallic core to silicate mantle among the terrestrial planets3 as well as an internal magnetic field4. Images from the Mariner 10 spacecraft reveal lobate scarps, so called because of their curved or scalloped edges, which have been interpreted to be high-angle thrust faults5,6,7,8 resulting from a period of global contraction. A range of mechanisms has been invoked to explain the stresses leading to global contraction, including cooling and core formation5,9, tidal effects due to gravitational interactions with the Sun10, mantle convection11 and the impact that formed the Caloris basin12. Here I present numerical simulations of the three-dimensional nature of convection within Mercury’s silicate mantle. The model yields a regularly spaced pattern of convection, in which upwelling regions of the mantle assume linear, sheet-like shapes at low latitudes and a nearly hexagonal pattern near the poles. The distribution of resultant surface stresses is consistent with the observed pattern of lobate scarps, suggesting that the compressive features record an ancient pattern of mantle convection11, in addition to global contraction. The gravity and topographic data returned from the MESSENGER 11 mission13 will help test this hypothesis.