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SUMMARY:Laboratory analogues for the settling and remelting of iron snow i
 n planetary cores - Quentin Kriaa\, DAMTP
DTSTART:20250430T130000Z
DTEND:20250430T140000Z
UID:TALK229924@talks.cam.ac.uk
CONTACT:Anna Walczyk
DESCRIPTION:In this seminar\, I will present several laboratory experiment
 s\, complemented by numerical simulations\, that aim at modelling iron sno
 w: What can we learn about the settling and remelting of iron crystals in 
 the planetary core of Ganymede (a natural satellite of Jupiter) which nour
 ish a compositional convection at the origin of the planet's magnetic fiel
 d? \n\nAs Ganymede gradually releases heat in space and cools down\, its i
 ron-rich core gradually solidifies. This solidification leads to the forma
 tion of pure iron crystals at the core periphery\, that subsequently sink 
 deep in the core due to gravity. The settling dynamics of a cloud of cryst
 als is modelled experimentally with particle clouds of sub-millimetric gla
 ss spheres settling in water. These clouds grow with depth due to the entr
 ainment of ambient water into the clouds. The canonical model of entrainme
 nt by Morton et al. 1956 would predict their growth rate to be unaffected 
 by the particles' size. Yet\, their growth rate is maximum for a specific 
 particle size. This optimum originates from the partial decoupling between
  the settling particles and the flow\, as explained with 3D two-way couple
 d Eulerian simulations.\n\nWhen iron crystals ultimately reach very large 
 temperatures deep in Ganymede's core\, they remelt. Their dense molten sno
 w drives a compositional convection that is assumed vigorous enough to pow
 er a magnetic field through dynamo. To test this assumption\, experiments 
 are conducted where sugar grains (aka the iron snow flakes) are continuous
 ly sieved above a water tank (aka the deep convective core). The size of g
 rains controls particle-scale interactions with the flow\, with a critical
  influence on the length scales and velocity scale of convection\, on the 
 laminar/turbulent nature of the flow\, and on the depth where sugar grains
  fully dissolve -- with paramount implications for the emergence of dynamo
  in Ganymede.\n
LOCATION:JDB Seminar RM
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