Dynamo action in planetesimals

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Recent measurements of remanent magnetization in meteorites showed that the field strengths are probably incompatible with ambient field capture or impact-generated fields. The proposed mechanism for the generation of magnetic fields in meteoritic material that has formed in planetesimals is a hydromagnetic dynamo. It was also shown that fluid material must have been present in a large variety of bodies in the early Solar System. The proposed project aims at the investigation of dynamo action in planetesimals. One of the generators may be convection driven by radioactivity or chemical differentiation of the melt, providing heat sources for a few million years. Another possible dynamo mechanism may employ the nutation-driven flows in the bodies, assuming that most planetesimals had nonspherical shapes. An extreme form of dynamo with forcing on the surface could be a collisional dynamo where external, abrupt changes of the rotation axis lead to topology changes of the magnetic fields, possibly exciting a dynamo in minor bodies of the Solar System. The existence of the latter dynamo is yet to be shown theoretically. If no dynamo is found, but the field is simply amplified by differential rotation, magnetic instabilities will be important for the magnetisation of those parts of the planetesimal which had already solidified.