METEOROID MORPHOLOGY AND DENSITIES - DECODING SATELLITE IMPACT DATA

The densities of interplanetary micrometeoroids have been inferred by various techniques in the past; a valuable (albeit indirect) technique has been the study of the deceleration profile of radar meteor trails , for example. Impacts on the thin foils of the Micro-Abrasion Package on NASA's LDEF satellite and the Timeband Capture Cell Experiment on ESA's Eureca satellite now provide direct in situ measurement of the c ross-sections diameters of impacting micrometeoroids and also of space debris particles. Combining these data with impact data from thick-ta rget impact craters, where the damage is mass-dependent, and where suc h targets have experienced a statistically identical flux, leads to a measure of the impactor density which is only weakly affected by the a ssumed impact velocity. Comparing the space result with those from sim ulations shows that the density distribution of interplanetary particl es in space has a more significant low density component than the dist ributions obtained by most other recent methods and that the mean dens ity is in the range 2.0 to 2.4 g cm(-3) for masses of 10(-15) to 10(-9 ) kg. The characteristic density - namely, the single value which woul d characterize the impact behavior of the distribution-is 1.58 cm(-3). Perforation profiles reveal that a large fraction of the largest part icles impacting the satellites are nonspherical but that typical aspec t ratios are mostly in the range 1.0-1.5. Flux distributions of the me teoroid population incident on the Earth at satellite altitudes are de rived in terms of mass and mean diameter. (C) 1998 Academic Press.