Detecting Sub-Micron Space Weathering Effects in Lunar Grains with
Synchrotron Infrared Nanospectroscopy
Abstract
Space weathering processes induce changes to the physical, chemical, and
optical properties of space-exposed soil grains. For the Moon, space
weathering causes reddening, darkening, and diminished contrast in
reflectance spectra over visible and near-infrared wavelengths. The
physical and chemical changes responsible for these optical effects
occur on scales below the diffraction limit of traditional far-field
spectroscopic techniques. Recently developed super-resolution
spectroscopic techniques provide an opportunity to understand better the
optical effects of space weathering on the sub-micrometer length scale.
This paper uses synchrotron infrared nanospectroscopy to examine
depth-profile samples from two mature lunar soils in the mid-infrared,
1500–700 cm-1 (6.7–14.3 μm). Our findings are broadly consistent with
prior bulk observations and theoretical models of space weathered
spectra of lunar materials. These results provide a direct spatial link
between the physical/chemical changes in space-exposed grain surfaces
and spectral changes of space-weathered bodies.