Is Mercury a volatile-rich planet?

Abstract

Data returned from the gamma-ray spectrometer onboard the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft have been interpreted to say that Mercury is a volatile-rich planet (elevated K/Th and K/U), which is important given its heliocentric distance. The MESSENGER X-ray spectrometer provided chemical information from the surface of Mercury which we used to calculate an average surface composition for the regions analyzed. The high S abundance and low FeO abundance of the surface indicates that the oxygen fugacity of the Mercurian interior is very reducing (-6.3 to -2.6 log f O2 units below the iron-wstite buffer). At these low oxygen fugacities, elements that are typically considered lithophile can become more siderophile or chalcophile. We review available metal/silicate partitioning data for K and U to show that Mercury's volatile inventory is still an open question, and additional experiments investigating metal/silicate partitioning at the conditions of Mercury's core formation are needed. © 2012 by the American Geophysical Union.