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Destruction and Observational Signatures of Sun-Impacting Comets

Motivated by recent data on comets in the low corona, we discuss destruction of sun impacting comets in the dense lower solar atmosphere. Perihelion distances q less than the solar radius and incident masses Mo much greater than 1E12 g are required to reach such depths. Extending earlier work on planetary atmosphere impacts to solar conditions, we evaluate the mechanisms and spatial distribution of nucleus mass and energy loss as functions of Mo and q, and of parameter X = 2Q/CHvovo. Q is the total specific energy for ablative mass loss, CH the bow shock heat transfer efficiency, and vo the solar escape speed (619 km/s). We discuss factors affecting Q and CH and conclude that, for solar vo, X is most likely less than 1 so that solar impactors are mostly ablated before decelerating. Sun impacting comets have kinetic energies 2E30 erg x(Mo/1E15 g), comparable with the energies of magnetic flares. This is released as a localised explosive airburst within a few scale heights H around 200 km of the photosphere, depending weakly on Mo , q and X. For X = 0.01, Mo around 1E15 g, and a typical Kreutz Group shallow incidence angle, comet the airburst occurs around atmospheric density n around 3E15 per ml and this would be 1000 times larger (700 km deeper) for vertical entry. Such airbursts drive flare like phenomena including prompt radiation, hot rising plumes and photospheric ripples, the observability and diagnostic value of which we discuss.