Meteoroid Morphology and Densities: Decoding Satellite Impact Data

et al. 1982, Zolensky et al. 1989, Flynn and Sutton 1991, Love et al. 1993). The recovery of space-exposed thin foils, The densities of interplanetary micrometeoroids have been however, presents the opportunity for further determinainferred by various techniques in the past; a valuable (albeit tions of the density from the perforation signatures of indirect) technique has been the study of the deceleration profile of radar meteor trails, for example. Impacts on the thin foils impacting meteoroids. This must, however, be combined of the Micro-Abrasion Package on NASA’s LDEF satellite and with the cratering record of a thick-target for exactly the the Timeband Capture Cell Experiment on ESA’s Eureca satelsame pointing history of space exposure in order to elimilite now provide direct in situ measurement of the cross-sections nate any assumptions of calibration or space environment diameters of impacting micrometeoroids and also of space de(flux distributions). Such data are here presented from bris particles. Combining these data with impact data from the LDEF Micro-Abrasion Package (MAP) experiment thick-target impact craters, where the damage is mass-depen(McDonnell et al. 1993) which exposed thin foils of thickdent, and where such targets have experienced a statistically nesses 1.5–30 em. identical flux, leads to a measure of the impactor density which By scanning the flux distribution on thin foils (perforais only weakly affected by the assumed impact velocity. Comtions) and on thick targets (craters) where both have been paring the space result with those from simulations shows that exposed to the same flux, we can obtain a measure of the density distribution of interplanetary particles in space has particle density. Information on particle density arises bea more significant low density component than the distributions cause different mechanisms are involved in the two target obtained by most other recent methods and that the mean types. For example, in thin foils (of thickness f ) intermedidensity is in the range 2.0 to 2.4 g cm for masses of 10 to ate sized particles (of diameter dp P f) can cause a hole 10 kg. The characteristic density—namely, the single value of around 5 times the particle diameter (Hörz et al. 1995), which would characterize the impact behavior of the distribuwhile very large particles (say dp . p20f) effectively tion—is 1.58 cm. Perforation profiles reveal that a large frac‘‘punch out’’ their cross-sections (size). For a thick target, tion of the largest particles impacting the satellites are nonimpact-crater dimensions are more mass-sensitive; the respherical but that typical aspect ratios are mostly in the range sultant thin-foil damage may also be used to obtain the 1.0–1.5. Flux distributions of the meteoroid population incident on the Earth at satellite altitudes are derived in terms of mass aspect ratio of the impacting particles. and mean diameter.  1998 Academic Press Previous workers (e.g., Paley 1992, Deshpande 1993,