Cooper et al. reply —

Taylor et al. argue that documented differences between laser diffraction and sieving techniques1, rather than degradation of the samples over time, can explain the different particle size distributions of lunar soil samples that we observe. However, we would expect comparatively larger particle sizes for laser diffraction measurements if this were the case; instead, our laser diffraction measurements yielded smaller values. We find that methodological differences cannot account for the discrepancy between the two sets of measurements.

Taylor et al. further suggest that a valid comparison between the measurement techniques on a lunar soil sample has not been demonstrated. Although not discussed in our paper2, we performed sieve and laser diffraction measurements for a representative material and found good agreement in the results. Taylor et al. argue that the material used lacks the complexity, mineralogy and texture of a natural terrestrial or lunar soil, however neither sieving nor laser diffraction techniques avoid uncertainties introduced by irregularly shaped particles1. Furthermore, mineralogy should not affect the laser diffraction measurements because minerals in the lunar soils do not interact with the carrier fluid (isopropanol). Various fluids were used in sieving, so the suggestion that water affected the sieve results applies to only a few cases.