Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 2K083

Thermal Processing of Solids though the Short Circuit Instability

McNally, C.P. (Niels Bohr International Academy, Niels Bohr Institute, University of Copenhagen)
Hubbard, A. (American Museum of Natural History)
Mac Low, M.-M. (American Museum of Natural History)
Ebel, D.S. (American Museum of Natural History)
D\'Alessio, P. (Centro de Radioastronomia y Astrofisica, UNAM)

The turbulent magnetohydrodynamic flow in the inner regions of a protoplanetary disk forms thin current sheets. These sheets are sites of magnetic reconnection and dissipate the magnetic fields amplified by the disk dynamo. In our own solar system, meteorites record a history of intermittent heating events: meteoritic chondrules were formed in the early Solar System by brief heating of silicate dust to melting temperatures. We suggest that our recently described short-circuit instability concentrates the heating in current sheets enough heat precursor grains for chondrules and other high-temperature minerals. By including the effects of radiative cooling, taking into account the extremely sharp temperature dependency of the opacity, we find two classes of short-circuit event with peak temperatures of ~1600K and ~2100K, set by the dust destruction temperature and the saturation of potassium ionization. The volume-filling nature of turbulent magnetic reconnection is compatible with constraints from formation of high temperature minerals: continuous processing over millions of years in the early solar system, the occurrence of igneous rims, compound chondrules, chondrule-matrix complementarity, and chondrule-chondrule complementarity. The same short-circuit mechanism may perform high-temperature mineral processing continuously in protoplanetary disks, producing not just chondrules but also crystalline silicates and CAIs. As the mechanism is most efficient at the lowest temperatures where the disk is magnetically active, the inner edge of a dead zone is a particularly important region for short-circuit heating events. As the edge of the dead zone moves, both secularly and during outbursts (such as FU Ori), large regions of the inner disk may experience short-circuit heating events.

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