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The Diviner Lunar Radiometer Experiment on LRO includes three channels near 8 microns, selected to measure the Christiansen Feature (CF). The wavelength position of the CF is particularly sensitive to the major crystalline components of lunar rocks and soils. Diviner observations of the Apollo landing sites demonstrate a close correlation between CF values and FeO abundance in soil samples.
This relationship extends to pyroclastic glass beads (23 wt.% FeO), sampled at Apollo 17, that are derived from the Taurus-Littrow dark mantle deposit (DMD). With the inclusion of these samples, the CF correlation spans the entire range of FeO concentrations measured in Apollo soils. This provides a new dataset for remotely assessing soil FeO abundances across the lunar surface.
Pyroclastic glasses are found in many lunar soils, and 25 distinct compositions have been documented. In most cases, the source deposit has not been identified. The Sulpicius Gallus DMD, on the western edge of Mare Serenitatis, contains local concentrations of red and orange material thought to be pyroclastic glass. This deposit has a higher albedo than the deposit at Taurus Littrow, suggesting different compositions or different degrees of crystallization. Diviner CF values, averaged over 1 x 1 km areas, correspond to an FeO concentration of 19 wt.% -- significantly lower than the Taurus-Littrow samples but within the range of all pyroclastic glass compositions in lunar soils. Work is now underway to analyze the entensive DMD on the Aristarchus plateau, as well as similar deposits across the lunar surface.
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