Optical Properties of Asteroid Surface Alteration

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Dr. McFadden's research will have two phases: (1) Laboratory analytical experiments simulating the effects of solar wind on asteroid surfaces and the way these changes affect spectral reflectance and other optical properties. (2) Comparison of the laboratory results with remote sensing data made with respect to spectral reflectance and polarimetric and photometric scattering properties. This will define which of these parameters are diagnostic of solar wind bombardment and also define asteroid surface conditions whose specific spectral signatures are attributable to the effects of surface alteration. Understanding the chemical and physical states of asteroids and their evolutionary history has been impeded by investigators' inability to satisfactorily compare remote sensing measurements with certain samples of meteorites and synthetic mixtures of terrestrial materials. Dr. McFadden's study will examine the effects of solar wind bombardment on the reflectance and other optical properties of meteorite samples and mineral mixtures. This will improve the understanding of the relationship between asteroids and their possible meteoritic analogues, and test the current primary assumption in interpretation of asteroid spectral reflectance: that the surfaces of asteroids are represented appropriately by unaltered meteoritic materials.