Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21733907m&link_type=abstract
American Astronomical Society, AAS Meeting #217, #339.07; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
Induction heating is a process originally proposed by Sonett et al. to explain thermal processing of asteroids, some of which were heated to temperatures >1000 K in the solar nebula. In the scenario of Sonett et al., the asteroids were heated during the Sun's T Tauri phase by a dense, fully-ionized solar wind. In their view an asteroid exposed to such a wind would "see” a motional electric field E=-v/c x B, where v is the wind velocity and B is the magnetic field in the wind's rest frame. If correct, the resulting electric polarization of the asteroidal material would produce electrical currents and heating via Ohmic dissipation. We revisit the induction heating mechanism to assess its possible relevance to planetesimals in weakly-ionized protoplanetary disks, where large magnetic fields of 0.1-1 G are predicted on a variety of grounds. Due to the high densities of these disks, we adopt a fluid approach for the plasma. We point out that E=-v/c x B is strictly speaking the electric field far from a planetesimal, where the plasma streams freely. At the planetesimal surface, viscous forces in a shear layer bring the plasma to rest and the motional electric field vanishes. We show that there is nevertheless a nonvanishing electric field produced indirectly via magnetic field perturbations in the shear layer. We calculate these perturbations by solving the equations of nonideal MHD, including Ohmic dissipation, the Hall effect, and ambipolar diffusion. We use these results to find the electric field in- and outside a planetesimal and give quantitative estimates of the rates of heating by Ohmic dissipation, viscous dissipation, and energy dissipation associated with ambipolar diffusion.
Menzel Raymond L.
Roberge Wayne
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