Laboratory Emission, Visible-near Infrared, and Mössbauer Spectroscopy of Iron Sulfates: Application to the Bright Paso Robles Soils in Gusev Crater, Mars

Introduction: The Mars Exploration Rover (MER) in Gusev Crater has exposed in its tracks an unusual occurrence of a soil high in sulfur and high in phosphorus [1, 2] at a site called Paso Robles (Fig. 1). This salty soil is thought to be composed of the following: Fe-, Mg-, and Ca-sulfates; Ca-phosphate; hematite, halite, allophane, and amorphous Si [1]. We are currently studying a large suite of sulfate minerals [e.g., 3-7] using a variety of methods including midinfrared emission, reflectance, and micro-transmission spectroscopies, plus visible-near infrared (VNIR) spectroscopy and Mössbauer (MB) spectroscopy. Prior to our work, only the most common sulfates had been studied in detail in the literature using our wide variety of spectroscopic techniques. Included in our sulfate studies are numerous Fe sulfates that are clearly an important mineral phase of the anomalous Paso Robles soils. Hence, we are beginning to apply our spectral databases to the interpretation of various MER datasets to further explore and better understand the chemistry of these salt-rich soils. The focus of this work is to present sulfate emissivity, VNIR, and Mössbauer spectra.