The Mineralogy and Chemistry of Micrometeorites

Prior to their retrieval from low Earth orbit (LEO), the individual solar cells that make up the ‘-V2’ solar array panel from the Huhble Space Telescope (HST) were prone to hypervelocity (>5 k d s ) impact damage from micrometeoroids and space debris. The analysis of such passive collector surfaces allows sampling of micrometeoroids that have not undergone any terrestrial atmospheric alteration and better defines the population of space debris particles below the lmm size range. Herein a new approach has been taken to try and identify the nature atid origin of impact derived residues generated in the individual solar cells from the HST. A total of 25 solar cells were selected on the basis that they contained impact craters (100-1000pin diameter) rather than larger impact holes ( 1 -3mm diameter), as preliminary studies indicated that they were more likely io retain impact residues. These were suhsequently analysed using digitised hack-scattered electron imaging, coupled with digitised x-ray elemental mapping and micro-spot analysis to locate, identify and classify the residues. 29 impact craters were located on solar cells. In the analysis of the residues; 3 were identified residues as space debris in origin, 6 unclassified and 20 as micrometeoroid. The space dehris derived residues wcre identified as remnants of a point fragment, a stainless steel particle and a fragment of a printed circuit board. The micrometenroid derived residues were sub-classified in terms of mineral chemistry, with apparent inaficand phyllosilicates being the dominant components, with minor iron-nickel metal and iron sulfides, suggesting a broadly chondritic origin. Fe-Ni rich residue was also identified that would appear to belong to a group of non-chondritic particles previously unrecognised. Possible refractory or CdAI rich inclusions from a primitive micrometeoroid were also