A newly-identified spectral reflectance signature near the lunar South pole and the South Pole-Aitken Basin

Faith Vilas,Wendell W Mendell,Lucy A Mcfadden,Cassandra J Runyon,Elizabeth A Jensen,Deborah L Domingue

doi:10.1186/bf03352763

Faith Vilas, Wendell W Mendell + Show 4 more

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https://doi.org/10.1186/bf03352763

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Abstract

Abstract Signal analysis of Galileo images of the Moon suggests the presence of an absorption band centered near 0.7 μm in the reflectance spectra of areas located adjacent to the equatorward walls of lunar craters at latitudes ranging from −58 to −78°, and areas contained in the South Pole-Aitken Basin. We propose three potential explanations: an Fe2+→Fe3+ charge transfer transition in oxidized iron in clinopyroxenes (high-Ca bearing pyroxenes) or phyllosilicates (Fe- and Mg-bearing sheet silicates containing adsorbed H2O and interlayer OH−), or an effect of titanium in ilmenite (a common lunar opaque material). No identification of the mineralogy is conclusive. The presence and nature of the absorption feature could be confirmed using AMICA images of the lunar far side from the Japanese mission Hayabusa, spectroscopic results from the Japanese mission Selene scheduled for launch in 2007, or the Moon Mineralology Mapper on the Indian mission Chandrayaan-1.

Highlights

We used Galileo Solid State Imager (SSI) images taken through the GRN, RED (670 nm, 60 nm), 756 nm (18 nm), and 889 nm (120 nm) broadband filters to search for spectral evidence of aqueous alteration near the lunar South pole by detecting signs of a broad (∼260 nm wide) yet weak absorption feature in the lunar reflectance spectrum centered near 0.7 μm
A spatial unit represented by a pixel containing 25 to 33% antigorite produces the RED filter inflection we found near the lunar South pole
Near the lunar South pole, these regions all consist of rough, hilly terrain separate from the equatorward walls of large craters, representing areas where the surface material appears to have been churned through previous surface event or events

Summary

Motivation and Background for Search for Lunar Phyllosilicates

Spectral observations of reflected sunlight from the surface of a planetary regolith serve as a remote sensing probe of surface mineralogical composition and particle state. We used Galileo Solid State Imager (SSI) images taken through the GRN (central wavelength = 560 nm, width = 60 nm), RED (670 nm, 60 nm), 756 nm (18 nm), and 889 nm (120 nm) broadband filters to search for spectral evidence of aqueous alteration near the lunar South pole by detecting signs of a broad (∼260 nm wide) yet weak (expected absorption of 2–5%) absorption feature in the lunar reflectance spectrum centered near 0.7 μm. The SPA regions with 0.7-μm absorption features do not correlate with walls of large craters

Testing the Veracity of the Absorption Feature Signature

Findings

Possible Origins for the Observed Absorption Feature