Two-phase magnetohydrodynamics: Theory and applications to planetesimal cores

Publication date: Available online 7 February 2020Source: Physics of the Earth and Planetary InteriorsAuthor(s): David Bercovici, Elvira MulyukovaAbstractCore freezing and resultant compositional convection are likely important drivers for dynamo activity in large terrestrial bodies like the Earth. The solidification of compositional mixtures, such as iron and sulfur, generates mush zones of partial melt at the freezing front, which can eject chemically buoyant or heavy liquid that then drives convection. For smaller bodies such as planetesimals in the asteroid belt, conditions for generating a dynamo are harder to achieve. Nevertheless, evidence for magnetization of achondrite meteorites is abundant, suggesting that many planetesimal cores were somehow magnetized. As such small bodies cool rapidly under low gravity they likely spend much of their evolution with a large poorly compacted partial melt mushy zone. The magneto-hydrodynamic behavior of a deformable partial melt zone can induce magnetism via separation of solid and liquid phases, and conversely magnetism can impose extra forces on the phase separation in the mush zone. To this end, we have developed a new two-phase magneto-hydrodynamic theory for deformable mushes and slurries. The model includes the standard effects of Lorentz forces, and the competition between magnetic field stretching and diffusion. There are additional effects at the liquid pore or solid grain scale, which involve the interaction between phase...

Source: Physics of the Earth and Planetary Interiors - February 7, 2020 Category: Physics Source Type: research