Is Mercury a volatile-rich planet?

• Published in: Geophysical research letters Vol. 39; no. 9
• Main Authors: McCubbin, Francis M., Riner, Miriam A., Vander Kaaden, Kathleen E., Burkemper, Laura K.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01-05-2012; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: Abundance; core; Earth sciences; Earth, ocean, space; elemental partitioning; Exact sciences and technology; experimental petrology; Fugacity; Gamma rays; Geochemistry; Geophysics; magma ocean; Mercury; MESSENGER; Mineralogy; oxygen fugacity; Partitioning; Petrology; Planetology; Planets; Silicates; Spacecraft; Spectrometers; experimental studies; wüstite; gamma rays; oxides; buffers; mercury; abundance; X-rays; metals; Review; inventory; fugacity; Messenger space probe; drill cores; planets; Heliocentric distance; iron; silicates; oxygen; volatiles
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2012GL051711

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 logfO2units below the iron‐wüstite 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.
Key Points
Mercury's oxygen fugacity is the lowest of the terrestrial planets
Mercury could be volatile‐depleted, which is masked by its low oxygen fugacity
Experimental data applicable to magmatic systems on Mercury are very limited