Cao, Hao ; Soderlund, Krista M. ; Steinbrügge, Gregor ; Liu, Dunyu ; Dumberry, Mathieu ; Rivoldini, Attilio ; Schubert, Gerald

Talk presented at AGU 2023 San Fransisco on 2023-12-13

Abstract: Mercury, the innermost planet in the solar system, remains an enigma after the wealth of measurements collected by the NASA MESSENGER mission. The state of Mercury's iron-rich core and the dynamo action that generates Mercury’s relatively weak, axially aligned, yet north-south asymmetric internal magnetic field is not well understood. Here we investigate the dynamo action associated with one unique possibility of Mercury's core structure: a double-iron-snow (DIS) dynamo with an extended, stably stratified basal iron snow zone. This double-iron-snow structure model is one possible scenario that fits most other geophysical observations, including the moment of inertia and 88-day libration amplitude. Our three-dimensional numerical dynamo survey of the convective forcing, relative electrical conductivity, and Brunt-Väisälä frequency revealed that although a relatively weak surface magnetic field (with Elsasser number ~10-4) can be achieved within this set-up, the external magnetic field remains highly dipolar and north-south symmetric. This symmetry preference is due to the magnetic anchoring effect of the basal iron snow zone. Our results indicate that while the existence of a top iron-snow zone (or a stably stratified layer) can lead to a weak and more axisymmetric magnetic field, the existence of an extended basal iron-snow zone would prohibit the equatorial symmetry breaking in the magnetic field observed at Mercury. Thus, our dynamo modeling effort argues against the existence of an extended basal iron snow zone inside Mercury's core at present.

Note: GP24A-07
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Funding: 3PRODPLANINT/3PRODPLANINT/3PRODPLANINT