Experimental Measurement of Water Bands in Anhydrous Minerals to Improve Modeling of Adsorbed and Bound Water on the Regoliths of Inner Solar System Airless Bodies

Abstract:

Investigating the characteristics of H2O/OH-absorption bands is critical for understanding their abundance and adherence to remotely observed surfaces. Our goal is to experimentally measure the spectra of anhydrous minerals in thin section and as powders to distinguish between internal H2O, surface adsorbed H2O, adsorbed OH, and OH that was formed as a result of irradiation. From these spectra, we are developing a model that will allow us to better deconvolve the abundance of adsorbed H2O and internally bound OH-/H2O in these materials. With this model, we aim to be able to remove the effects of terrestrial adsorbed H2O, thus enabling us to use the dry spectra to model these materials in the regoliths of airless bodies found in the inner solar system. To complete this task, we created un-mounted thin sections of two ordinary chondrite meteorites (Kilabo – LL6 and Gao-Guenie – H5) and eight ultramafic and banded rocks collected at the Stillwater Intrusion to serve as analogs for the Earth’s moon. These rocks host an abundance of three key mineral series of interest: olivine, pyroxene, and plagioclase. We conducted EDS scans of each rock to create an elemental map and assess the specific mineral composition of phases in each sample. Transmittance spectra of each thin section were also collected from the visible through mid-IR range using the FTIR microscope to characterize bound water in each sample. These thin sections will be heated up to ~1000°C in a vacuum to remove any internal water and will be measured in transmission for a second time to determine their true anhydrous spectral baseline. Subsets of the samples have been powdered and will be measured under ultra-high vacuum conditions at temperatures ranging from ~293K to 650K to examine the spectral parameters for adsorbed terrestrial water on each sample. Ultimately, these powdered samples will be used for space weathering experiments to examine the nature of the OH- bands induced by irradiation.