Convection and Dynamos in Planetary Interiors

Lead Research Organisation: Newcastle University
Department Name: Sch of Maths, Statistics and Physics

Abstract

Many planets have a magnetic field that is generated by a dynamo process from the motion of conducting fluids inside planetary interiors, such as in the Earth. In magnetohydrodynamics (MHD), convection in a rotating, electrically conducting fluid acts to maintain a magnetic field. In a planet this fluid is driven by gradual cooling in the interior of the planet. This can happen if the convection is able to produce a magnetic field strong enough to alter the structure of the convective flows. Interestingly, some planets such as Mars do not presently have a magnetic field, but show evidence of having one in the past. The Mars Global Suveryor revealed that the rocks on the surface have strong remnant magnetisation despite there being no global magnetic field (Acuna et al. (1999)). Studies observe that the cessation of the Martian dynamo occurred rapidly (Lillis et al. (2008)). One possible cause of this sudden termination is subcritical dynamo action. That is, dynamo action for convective forcing below the threshold necessary for convective motions to occur in the absence of magnetic fields.

In the subcritical regime, the energy required to sustain the dynamo is far less than required to initiate the dynamo devoid of the strong magnetic field. Since the energy in the subcritical regime is lower than that required to generate the dynamo, if the Martian dynamo was ceased then it may not be possible for it to restart. This is the scenario that I will explore in my thesis. Note that other theories have been evoked to explain the cessation of the Martian dynamo, such as a giant impact (Roberts et al. (2009)).

The aim of my thesis project is thus to:
* determine the effects of the magnetic field on the convective behaviour and the efficiency of heat transport
* study the effects of rotation and differing properties of the fluid on the possible existence of a subcritical dynamo
* investigate whether or not the existence of a solid inner planetary core affects the subcritical dynamo

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
ST/R50497X/1 01/10/2017 30/09/2021
1949517 Studentship ST/R50497X/1 01/10/2017 30/06/2021 Robert George Cooper