The collection of micrometeoroid remnants from low earth orbit

The solar array panel returned from the Hubble Space Telescope after 3.62 years of space exposure offered the opportunity to study individual solar cells for hypervelocity impact damage and residue. A detailed electron microscope investigation of impact craters (100-1000 mu m diameters) has identified that most are residue-rich and by digitised x-ray elemental mapping and semi-quantitative micro-spot analysis the original precursor composition of the impactor can almost unambiguously be identified. The residues contain diverse elemental compositions that can be associated with known meteorite mineralogies and directly compared with interplanetary dust particles and micrometeorites, possibly the most likely source object. The observation of a magnesium-rich residue with (Mg+Fe) / Si ratio similar to that of forsterite (end-member Mg-olivine identified in meteorites), indicates that it is possible in favourable conditions to define clearly the compositional nature of the impactor. The identification of near-intact calcium-rich fragments, that are neither artefacts nor contamination, indicates that volatile chemistries can survive hypervelocity impacts in brittle glass substrates. The abundance of micrometeoroid residues in the individual solar cells has highlighted that valuable information can be retained from impact craters in returned space hardware which are essentially not designed as a dust collectors. (C) 1999 COSPAR. Published by Elsevier Science Ltd.