Radiation study of two very bright terrestrial bolides and an application to the Comet S-L 9 collision with Jupiter

Lightcurves and spectra of two of the brightest photographed bolides were studied. The Sumava bolide reached -21.5 absolute (i.e., 100 km distance) magnitude. This fragile cometary body of initial mass of about 5000 kg exhibited many flares and disappeared at an altitude of 59 km above the surface. The Benesov bolide (-19.5 mag) was a stony body of initial mass of about 13,000 kg which radiated down to 17 km of altitude and exhibited a bright flare at 24 km accompanied with severe fragmentation. It is shown that the fragmentation was the main mode of ablation. By modeling the lightcurve of Sumava it is found that about 85% of the initial mass was lost in five subsequent breakups. Even between the breakups, the ablation coefficient is found to be much higher than the theoretical value for melting and vaporization. The spectra show that the radiation of both bolides was produced by a gas heated to 4000-5000 It. At this temperature only the ablated material radiates; the radiation of the atmosphere was negligible. Atomic and molecular emissions are dominant for most of the trajectory, but near the maximum light thermal continuous radiation is also present. The results were generalized for the entry of the comet Shoemaker-levy 9 into the Jupiter atmosphere. Due to the high ablation, the cometary nuclei are not expected to penetrate below the jovian clouds. As the radiating volume of the associated bolides is optically thick, the bolides remain relatively faint and only weak dependence of the bolide brightness on the impactor mass is produced. The results are in accordance with the bolide and fireball observations from the Galileo spacecraft. (C) 1996 Academic Press, Inc.