Modeling snow regime in cores of small planetary bodies.
Authors: Ch.-Ed. Boukaré, Marc Parmentier, Yanick Ricard and Steve Parman
Observations of present day magnetic field on small planetary bodies such as Ganymede or Mercury challenges our understanding of planetary dynamo. Several mechanisms have been proposed to explain the origin of magnetic fields. Among the proposed scenarios, one family of models relies on snow regime.
Snow regime is supported by experimental studies showing that melting curves can first intersect adiabats in regions where the solidifying phase is not gravitationaly stable. First solids should thus remelt during their ascent or descent. The effect of the snow zone on magnetic field generation remains an open question.
Could magnetic field be generated in the snow zone? If not, what is the depth extent of the snow zone? How remelting in the snow zone drive compositional convection in the liquid layer? Several authors have tackled this question with 1D-spherical models. Zhang and Schubert, 2012 model sinking of the dense phase as internally heated convection. However, to our knowledge, there is no study on the convection structure associated with sedimentation and phase change at planetary scale.
We extend the numerical model developped in [Boukare et al., 2017] to model snow dynamics in 2D Cartesian geometry. We build a general approach for modeling double diffusive convection coupled with solid-liquid phase change and phase separation. We identify several aspects that may govern the convection structure of the solidifying system: viscosity contrast between the snow zone and the liquid layer, crystal size, rate of melting/solidification and partitioning of light components during phase change.
I will present this work at AGU 2017, New Orleans.
Related paper:
C.E. Boukaré, Y. Ricard, 2017, Modeling phase separation and phase change for magma ocean solidification dynamics, G3, doi: 10.1002/2017GC006902.
I will present this work at AGU 2017, New Orleans.
Caption: Snow pattern during solidification. Solids crystallize at the bottom of the domain, float (they are buoyant) and remelt (they cross the liquidus). Crystal size (large epsilon values means large crystals) which controls the ascension velocity, affects the convective structure. Planetary core solidification at low pressure might occur in similar fashion.
C.E. Boukaré, Y. Ricard, 2017, Modeling phase separation and phase change for magma ocean solidification dynamics, G3, doi: 10.1002/2017GC006902.