Coraor, Aron - Simulating surface materials: Preparation for the Exploration of Airless Bodies

The spectral data of samples and surfaces of the Moon, Near Earth Asteroids, Phobos, and Deimos will provide invaluable information of the geochemical state of these bodies, necessary for guiding human exploration and sample return. In keeping with the RIS4E goals, we have initiated experimental synthesis of minerals under simulated airless body conditions in order to optimize interpretation of remote sensing data sets and for investigation of the spectral effects of simulated space weathering. Initial efforts have been directed towards assessing the potential for using Fe in plagioclase to distinguish lunar feldspathic terrains, terrains that otherwise are characterized by limited variability in plagioclase composition. For lunar plagioclase, the Fe and Mg contents may rival the abundance of Na.
We will report here the results of our efforts to synthesize anorthitic plagioclase with variable Fe contents. The synthesis experiments were designed to grow plagioclase that (i) is in equilibrium with a melt that would stabilize olivine at a lower temperature, but at higher temperature has only plagioclase on the liquidus, (ii) is in equilibrium with metallic Fe, and (iii) is from a melt in which early spinel stabilization has been avoided by the addition of some additional excess silica in the mix (which adds a pyroxene component to the melt). The synthesis experiments involved loading Fe capsules with a well-homogenized mixture of oxides, silicates, and Feo sponge + hematite (to make FeO), placing the capsules (with a constrictor ring to prevent escape of silicate melt) into silica glass tubes and then evacuating these tubes before loading them with enough N2 to provide about an atmosphere of pressure at the synthesis temperature. These tubes were placed in a platform furnace and heated above the liquidus, and cooled to a temperature that remained above the saturation temperature of mineral phases other than plagioclase. Characterization of the material requires consideration of the analytical challenges inherent to low Na compositions and the possibility of secondary Fe-fluorescence when droplets of metallic Fe are present in the plagioclase.
Once these materials have been well characterized compositionally and used for Vis-NIR and mid-IR studies, these samples will be used for dust toxicity studies.