Birth and Decline of Magma Oceans in Planetesimals: 1. Experimental Study of Erosion and Deposition of Particles in an Internally Heated Convecting Fluid
Abstract
This paper is the first of two companion papers presenting a theoretical and experimental study
of the evolution of crystallizing magma oceans in planetesimals. We aim to understand the behavior of crystals
formed in a convective magma ocean, and the implications of crystal segregation for the thermal and structural
evolution of the convective system. In particular, we wish to constrain the possibility to form and preserve
cumulates and/or flotation crusts by sedimentation or flotation of crystals respectively. We use lab-scale
analog experiments to study the stability and the erosion of a floating lid composed of plastics beads lying
over a convective viscous fluid volumetrically heated by microwave absorption. We propose a law for erosion
and re-entrainment that depends only on two dimensionless numbers that govern these phenomena: (a) the
Rayleigh-Roberts number, characterizing the vigor of convection and (b) the Shields number, that encompasses
the physics of the flow-particle interaction. We further consider the formation of a cumulate at the base of
the convective layer by sedimentation of beads that are denser than the fluid. We find that particle deposition
occurs at a velocity that scales with the Stokes velocity, a result consistent with previous experimental studies.
We build up a model that describes the transient evolution of the convective system's thermal state and the
fraction of particles that segregated from the flow or that remain in suspension.
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JGR Planets - 2022 - Sturtz - Birth and Decline of Magma Oceans in Planetesimals 2 Structure and Thermal History of Early.pdf (2.2 Mo)
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