Inefficient compaction effect in small planetary cores

Abstract:

Growth of the solid inner core is generally considered to power the Earth's present geodynamo. Cristallisation of a solid central inner core has also been proposed to drive the lunar dynamo and to generate a magnetic field in smaller bodies. We estimated the compaction of planetary cores for different scenarios of growth and size of an inner core. Our main results indicate that small inner cores are unlikely to compact efficiently the liquid trapped during the first steps of the growth. This is especially true for small bodies for which the typical size of the core is similar to the compaction length. The light elements are thus trapped during the cristallisation, decoupling the release of latent heat and of light elements that are powering the geodynamo. We present a model to include the effect of an inefficient compaction in the energy budget and investigate the implications for the dynamo evolution in small bodies.