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)
Abstract:
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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