Evaluation of mineralogical alteration of micrometeoroid analog materials captured in aerogel Original Research Article

Silica aerogel has been used as a capturing medium for micrometeoroids and space debris. Several previous investigations suggest that aerogel could capture hypervelocity particles macroscopically intact. However, it has not been fully evaluated whether retrieved grains retain their pristine mineralogy. This study attempts to evaluate the intact survivability of high-speed projectiles in aerogel using impact experiments. Such experiments are essential for rigorous examination or further scientific discussion on the samples of on-going and future sample return missions in which aerogels are/will be used as capturing media. We fired two kinds of micrometeoroid analog materials into aerogel with a two-stage light gas gun (2–4 km/s), serpentine and cronstedtite, which are commonly found in CM/CI, and CM chondrites, respectively. As these hydrated minerals are broken down into anhydrous ones at relatively low temperatures, it is suitable for the evaluation of thermal alteration during the capturing process. The retrieved residues were examined with SEM/EDS, Synchrotron Radiation-XRD, and TEM/EDS. The SR-XRD analysis revealed that most of the volumes of residues are mineralogically unaltered. TEM observations show that one serpentine grain shot at 4 km/s has an unaltered crystalline part inside, an amorphous layer, and the outermost molten aerogel layer. One cronstedtite grain shot at 3 km/s, also examined by TEM, was found to have an unaltered interior as well as a vesiculated silicate melt layer. Image analysis revealed both mineral grains reduced their volume down to 10% of the original on average. These results suggest that it is possible to capture serpentine and cronstedtite particles mineralogically intact with the aerogel, at least in the interior of each particle, below 4 km/s, in spite of their large volume loss.