Optical maturity variation in lunar spectra as measured by Moon Mineralogy Mapper data

Abstract

[1] High spectral and spatial resolution data from the Moon Mineralogy Mapper (M 3 ) instrument on Chandrayaan-1 are used to investigate in detail changes in the optical properties of lunar materials accompanying space weathering. Three spectral parameters were developed and used to quantify spectral effects commonly thought to be associated with increasing optical maturity: an increase in spectral slope ("reddening"), a decrease in albedo ("darkening"), and loss of spectral contrast (decrease in absorption band depth). Small regions of study were defined that sample the ejecta deposits of small fresh craters that contain relatively crystalline (immature) material that grade into local background (mature) soils. Selected craters are small enough that they can be assumed to be of constant composition and thus are useful for evaluating trends in optical maturity. Color composites were also used to identify the most immature material in a region and show that maturity trends can also be identified using regional soil trends. The high resolution M 3 data are well suited to quantifying the spectral changes that accompany space weathering and are able to capture subtle spectral variations in maturity trends. However, the spectral changes that occur as a function of maturity were observed to be dependent on local composition. Given the complexity of space weathering processes, this was not unexpected but poses challenges for absolute measures of optical maturity across diverse lunar terrains.

Bulk hydrogen abundances in the lunar highlands: Measurements from orbital neutron data

“…While the bulk iron and titanium abundances across the FHT are mostly uniformly low (Lucey et al, 2000b;Lawrence et al, 2002), other bulk composition parameters, such as magnesium concentrations, do appear to show significant variations across the FHT (Prettyman et al, 2006;Peplowski and Lawrence, 2013) and in principle could be linked to compositional effects related to hydrogen retention. More recent measures of optical maturity (Nettles et al, 2011) show different compositional variations that can be compared to the derived hydrogen concentrations. All these dependencies could be investigated using multivariate analyses of the type that have been successfully carried out for compositional datasets at Mars (e.g., Karunatillake et al, 2012).…”

Lunar opposition effect as inferred from Chandrayaan‐1 M3 data

“…There is a problem related to residual band‐to‐band artifacts in the spectra caused by residual variability in the M 3 detector response that was not compensated with the flat field [ Nettles et al ., ; Green et al ., ]. In Figure a we present three spectra extracted from a fragment of the calibrated M 3 image M3G20090417T155652.…”

“…The photometric correction of M 3 images consists of two parts: the Lommel‐Seeliger function described limb‐darkening and the wavelength‐dependent phase function [ Lundeen et al ., ]. As we are interested in quantification of the wavelength dependence of BOE, we did not apply the Level 2 M 3 phase function [ Besse et al ., ], but corrected the data with the Lommel‐Seeliger function for consistency with many previous works [ Nettles et al ., ; Hicks et al ., ; Buratti et al ., ; Hapke et al ., ; Besse et al ., ]. This function is widely applied for planetary data, though it does not provide satisfactory accuracy at arbitrary illumination and observation [ Shkuratov et al ., , ].…”

Is the Linné impact crater morphology influenced by the rheological layering on the Moon's surface? Insights from numerical modeling

“…The continuous ejecta of Linné, which extends up to 8 km from the crater center, is indeed characterized by a high albedo emblematic of very young surfaces (e.g., Nettles et al. ).…”