Nanoscale Characterization of Space Weathered Lunar Samples

Abstract

High-resolution nanoscale Fourier transform infrared (Nano-FTIR) imaging and spectroscopy correlated with photoluminescence measurements of a lunar ilmenite basalt (12016) and recrystallized impact melt breccia (15445), Apollo samples with different origins and history, reveal distinct chemical differences associated with the parent-rock geochemistry and space weathering effects. Intrinsic or delivered Nd3+ and an amorphous silicate glass component produced by solar wind bombardment are observed on exterior surfaces, whereas intrinsic Cr3+ and/or trapped electron states likely produced by energetic x-rays or cosmic rays are observed in interior surfaces. Spatially localized 1050 cm-1/935 cm-1 band ratios in Nano-FTIR hyperspectral maps may reflect shock-induced nanostructures in the impact melt brecci, while shifts in silicate band positions may indicate general space-weathering. Collectively, the shock features, amorphous silicate over-layer, electron-trap states and differential Nd3+ and Cr3+ ratios provide compelling evidence and proxies for space weathering and transformation events not easily obtained with conventional far-field optical analysis techniques.