Light curves of very faint meteors

Abstract

THE variation of brightness as a function of height when a meteoroid burns up (ablates) in the Earth's atmosphere is governed by the physical properties of the meteoroid. The basic theory of the ablation of a solid meteoroid to due to Öpik¹, and the theoretical light curves are in fairly good agreement with the observed light-curves of very bright meteors². In contrast to this the observations of Jacchia³ and Hawkins and Southworth⁴ of faint photographic meteors show that the train lengths of these meteors are much shorter than predicted by the classical theory, and it is principally due to evidence of this sort that the “dustball” theory of Whipple⁵ which supposes the original meteoroid to consist of an aggregate of many small solid particles, has become very popular. Nevertheless Jones and Kaiser⁶ found that by extending the classical ablation theory to include the effects of the meteoroid's thermal capacity, conduction and radiation they could explain many features of the experimental data in terms of compact meteoroids which fragment as a result of thermal shock. According to Jones and Kaiser⁶ it is possible to choose between the two theories on the basis of observations of very faint meteors (magnitude M > + 3) since these meteoroids should not fragment due to thermal shock if they are compact; on the other hand if they are fragile conglomerates they will probably continue to show the effects of severe disintegration.