Ohmic heating of asteroids around magnetic stars

Abstract

We consider the impact of electromagnetic induction and Ohmic heating on a conducting planetary object that orbits a magnetic star. Power dissipated as heat saps orbital energy. If this heat is trapped by an insulating crust or mantle, interior temperatures increase substantially. We provide a quantitative description of this behavior and discuss the astrophysical scenarios in which it might occur. Magnetic fields around some main-sequence stars and white dwarfs are strong enough to cause the decay of close-in orbits of asteroids and dwarf planets, drawing them through the Roche limit on Myr time scales. We confirm that Ohmic heating around neutron stars is driven by the rotation of the stellar magnetic dipole, not orbital dynamics. In any case, heating can raise interior temperatures of asteroids or dwarf planets on close-in orbits to well above liquidus. Hot material escaping to the surface may lead to volcanic ejections that can obscure the host star (as in the light curve of KIC 8462852) and pollute its atmosphere (as observed with metal-rich white dwarfs). We speculate that mixing of a volatile-rich mantle or crust with material from an induction-heated core may lead to an explosion that could destroy the asteroid prior to tidal break-up.

36 pages, 5 figures, 2 tables, ApJ, accepted

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• Thermal Desorption of H2O-Ice: From Nanoscale Films to the Bulk
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• Measurement of stellar and substellar winds using white dwarf hosts
• Planetesimals drifting through dusty and gaseous white dwarf debris discs: Types I, II and III-like migration
• White dwarf magnetospheres: Shielding volatile content of icy objects and implications for volatile pollution scarcity
• The Decline and Fall of ROME. V. A Preliminary Search for Star-Disrupted Planet Interactions and Coronal Activity at 5 GHz Among White Dwarfs within 25 pc
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