Some effects of multiple impacts on the thermochemical evolution of Mars

Abstract

The early history of the terrestrial planets was strongly shaped by the occurrence of several large meteorite impacts. A large impact causes not only severe effects on geologically short timescales (i.e., on the order of seconds to centuries), but may also disturb the thermal structure of the mantle and core of a planet for millions of years. Numerical models have shown that even a single large impact can potentially suppress convection on a large scale and extinguish a core dynamo (e.g., Roberts and Arkani-Hamed, 2012; Arkani-Hamed and Olsen, 2010). This study combines numerical mantle convection models that include a detailed model of mantle mineralogy and chemistry and are coupled with a simple model of core energetics (e.g., Ruedas et al., 2013) with a parameterization of the thermal effects of an impact and a simple description of some aspects of the concomitant mass transport in order to improve existing models in terms of applicability to the real planet Mars. The effects of single and multiple giant impacts on the long-term evolution of the mantle and core of Mars are studied and an assessment is made whether traces of the early giant impacts - apart from the obvious craters - may have survived to the present day and could be observable by geochemical or geophysical methods. Of particular interest in this context are possible variations in the surface heat flow or in the trace element concentrations in the crust.