Wed 21st March @ noon, Rm 312.222

Abstract:

Thousands of exoplanets have been discovered in solar systems with a range of C/O ratios. This ratio has a large control on the oxygen fugacity under which planets in the systems form and evolve. In our solar system, the planet Mercury lies at the extreme low end of oxygen fugacity and may provide insights into how planets in high C/O star system will evolve. As oxygen fugacity decreases, sulfur becomes an important anion, and its solubility in silicate melts increases by 1-2 orders of magnitude. At the same time, the Fe contents of silicate melts all but disappears as FeS and/or Fe-metal are stabilized. Ca and Mg bond with S in the melt, reducing the stability of olivine and Ca-bearing phases such as plagioclase and clinopyroxene. The result is that while Mercury is similar in size to the Moon, its chemical and physical evolution is dramatically different. There is no anorthosite flotation crust, likely no overturn, and Mercury has an enormous metallic core, likely with high Si, S and/or C contents. Pyroclastic volcanism is much more common on Mercury than on the Moon, though what volatile species causes the explosive eruptions is not clear. In this talk I will go over what we know of Mercury from the MESSENGER mission and what we have learned from experimental studies at low oxygen fugacities. Combining the phase equilibria with dynamic models of magma ocean crystallization, I will describe some (highly speculative) models for the internal chemical layering in Mercury and its subsequent evolution.

Short bio:

I received my Ph.D. in Geology and Geochemistry from the Massachusetts Institute of Technology in 2001. I came to Brown after three years as Lecturer at Durham University, Great Britain. I am considered a leading expert on the behavior of volatiles in the Earth’s interior. My work on water in early Earth magmas is providing new insights into the thermal evolution of the Earth. Likewise, my recent research on noble gas solubility in the mantle is challenging the existing models of mantle structure and evolution.