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Motivated by recent data on comets in the low corona, we discuss destruction of 'sun-impacting' comets in the dense lower atmosphere.Perihelion distances q ≲ R ! and masses M o >>" 10 12 " g are required to reach such depths.Extending earlier work on planetary atmosphere impacts to solar conditions, we evaluate the mechanisms and distribution of nucleus mass and energy loss as functions of M o and q, and of parameter X = 2Q/C H v o 2 . Q is the total specific energy for ablative mass-loss, C H the bow-shock heat-transfer efficiency, and v o the solar escape speed (619 km/s). We discuss factors affecting Q and C H and conclude that, for solar v o , X is most likely < 1 and solar-impactors mostly ablated before decelerating. Sun-impacting comets have energies M o v o 2 /2 ~ 2x10 30 ×(M o /10 15 g) erg, (comparable to magnetic flares ~ 10 29-33 ). This is released as a localised explosive airburst within a few scale heights H ≃ 200 km of the photosphere, depending weakly on M o , q and X. For X = 10 -2 and M o = 10 15 g, ! 2! a shallow incidence (e.g. polar θ ~ cos -1 (0.01)) Kreutz comet airburst occurs at atmospheric density n ~ 3x10 15 cm -3 -a height of 700 km (3.5 H) above the photosphere (where n = n o = 10 17 cm -3 ). The airburst n scales as ~ (M o Xcos 3 θ ) 1/2 (while height z(km) = 200ln(n o /n)) so n increases 1000× (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.

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