Bolides produced by impacts of large meteoroids into the Earth's atmosphere: comparison of theory with observations
I. Beneov bolide dynamics and fragmentation
J. Borovika 1,
O.P. Popova 2,
I.V. Nemtchinov 2,
P. Spurný 1 and
Z. Ceplecha 1
Received 23 September 1997 / Accepted 12 January 1998
Detailed analysis of one of the largest and well documented bolides - the Beneov bolide (EN 070591) - has been performed. The bolide had an initial velocity of 21 km s-1, reached a maximal absolute magnitude of -19.5 at the altitude of 24 km and radiated down to 17 km. Detailed photographic data for the light curve, geometry and dynamics of the main body and several fragments are available. This enabled us to test the theoretical radiative-hydrodynamic model used previously for the analysis of satellite-detected bolides.
The conventional analysis produces a huge discrepancy between the dynamic (80-300 kg) and photometric (5000-13,000 kg) mass. The discrepancy might be removed assuming a low density of 0.5 g cm-3 but this is unrealistic. The radiative-hydrodynamic modeling yielded a mass of 2000 kg and density of 1-2 g cm-3. However, the dynamics was not sufficiently well reproduced.
There is direct observational evidence of meteoroid fragmentation at altitudes of 38-31 km and of catastrophic disruption at 24 km. These, however, do not explain the problem with the mass. The crucial point is that the bolide was significantly decelerated already at the altitudes between 50-40 km, while enormous luminosity was produced below 40 km. We suggest that the meteoroid must have been fragmented into 10-30 pieces of a mass of 100-300 kg already at an altitude of 60-50 km. By creating a progressive fragmentation model with two types of fragmentation at three different altitude levels, we were able to reproduce the dynamics and luminosity sufficiently well. The best estimate of the initial mass is 3000-4000 kg for a density of 2 g cm-3.
The comparison with the bolide PN 39434 suggests that the behavior of Beneov is typical for large stony meteoroids. Early fragmentation under dynamic pressures of the order of 1 Mdyn cm-2 is very important. The analysis of the light curve with the radiative-hydrodynamic model can give good order-of-magnitude estimates of mass, if no dynamic data are available.
Key words: meteoroids, meteors
Send offprint requests to: J. Borovicka, (email@example.com)
© European Southern Observatory (ESO) 1998
Online publication: May 15, 1998