The strength of cometary meteoroids:: clues to the structure and evolution of comets

Meteoroid behaviour during atmospheric interaction provides clues about the strength and density of cometary disintegration products, establishing a bridge between different research fields. We have estimated the strength of cometary meteoroids by studying meteor ablation light curves measured accurately from multiple-station meteor observation programmes. Our approach assumes that the typical height for meteoroid fragmentation is associated with the peak of meteor luminosity. The strength of cometary meteoroids is independent of the entry velocity and very similar for cometary streams with similar ages. Meteoroids from periodic comets have typical strength of similar to 10(4) dyn cm(-2). The only exception among the studied comets is the extremely fluffy particles from 21P/Giacobini-Zinner that exhibit similar to 4x10(2) dyn cm(-2). Finally, evolved bodies, e.g. 2P/Encke and 3200 Phaeton, release the toughest meteoroids. We suggest that the main physical difference between cometary particles reaching the Earth from several sources could be a different degree of compaction arising from different physical processing of cometary nuclei by collisional processes, thermal and, perhaps, aqueous alteration. Meteor data suggest that highly processed cometary nuclei produce the meteoroids with the largest tensile strength values while 'pristine comets' are producing meteoroids with the lowest strength values characteristic of bodies with a low degree of compaction.