The Martian dynamo

Abstract

Mars has a well-conducting core composed of a mixture of iron and sulphur. It is probably liquid and differentially rotating. The main problem is whether the core is stably stratified or convective. About 10–15% of sulphur is enough to drive a compositional convection over a great part of Martian evolution if an inner solid solid core was formed. Convection in a liquid rotating stratified core results in a mean helicity, which, together with differential rotation and turbulent magnetic diffusivity, is a source for mean field dynamo. The magnitude of the magnetic field generated can explain the origin of magnetization of the shergottie, nakhlite and chassignite meteorites. However, the dynamo probably does not work at present, in accordance with a weak large-scale magnetic field on the Martian surface estimated from the Mars-2, -3, -5, and Phobos mission results. This field is interpreted as an external product of the magnetized mantle having a slightly elliptical form. Some other possible explanations for the outer magnetic field are discussed.