Iron Mineralogy of Venus' Surface Investigated by Mössbauer Spectroscopy

Abstract

We discuss the use of Mössbauer (MB) spectroscopy to study Fe-bearing minerals on Venus' surface. At present, there is no direct information about the mineralogy of Venus' surface, although in situ chemical analyses by X-ray fluorescence (XRF) spectroscopy have been done by the Venera 13, 14, and Vega 2 spacecraft at three landing sites. The XRF elemental analyses are sensitive to major rock-forming elements heavier than sodium and show the presence of several mass percent iron. Normative mineralogical calculations model the Fe mineralogy at the Venera 13, 14, and Vega 2 landing sites, but the actual Fe minerals present are unknown. We calculate synthetic MB spectra for the normative Fe minerals at the Venera 14 and Vega 2 landing sites. Some calculations include several mass percent of the Fe oxides (magnetite, hematite) and sulfides (pyrite, pyrrhotite) that are frequently discussed in the literature as being present on Venus' surface. Our results indicate that the normative iron minerals at the different landing sites can be identified, quantitatively measured, and distinguished from each other using MB spectroscopy. We also find that about 1 mass percent of any of the different iron oxides and sulfides considered in our modeling should be detectable using MB spectroscopy. This is significant because the loaded dielectric model for low radar emissivity regions on Venus requires several mass percent of Fe-bearing phases. The temperature dependence of the MB spectra is also calculated. Finally, the implications of these results for future spacecraft missions to Venus using MB spectroscopy are discussed.