Anne M. Hofmeister

Additional Areas of Research

Heat Transfer

Thermal conductivity (k) or its close relative thermal diffusivity (D) plays an crucial role anywhere heat is exchanged, such as magmatism, mantle convection and evolution of diverse planetary bodies. Most of the available data on materials comprising planets and meteorites were collected using contact methods and contain systematic and opposing errors due to contact resistance and spurious radiative transfer. The only method which provides accurate and reliable values for semi-transparent materials such as silicates and oxides is laser-flash analysis. Such an apparatus is in operation in the mineral physics program at Washington U. It is the only such facility in geoscience world-wide.

Because of substantial errors in the measurements, heat transport in insulators has been misunderstood. Some of the work at Washington U. involves basic theoretical physics. The data gathered here are in reasonably good agreement with the damped harmonic oscillator model, which allows extrapolation to the deep Earth. Our best estimates are 5 to 10 times conventional numbers for the core mantle boundary and suggest a very stagnant lower mantle.

We are undertaking systematic study of D of diverse materials as a function of temperature. One focus is on high pressure phases such as perovskites. Methods for measuring D at pressure are underdevelopment. This program is in collaboration with J. J. Dong (Auburn University) with the goal of improved theory and measurements which will provide robust values to the core-mantle boundary. Applications to mantle convection are being made in collaboration with Dave Yuen (U. Minnesota). Application has been made to revising the global heat flux (with R. E. Criss in this department). We have shown that the current models used to provide this estimate do not conserve rock-mass. An improved model is underdevelopment.

Another focus is thermal diffusivity of continental crustal materials and their melts, as well as glasses, in collaboration with Alan G. Whittington and Peter Nabelek (U. Missouri, Columbia). Applications are underway to the continental geotherm, understanding thrust belts, and pluton assemblage. A search is underway for a postdoctoral assistant. New graduate students are welcome.

Dust in Space

Astronomical measurements of infrared spectra show signatures of dust superimposed upon stellar emissions. A first step in understanding the development of protoplanetary nebula is simply identification of the dust that exists in space. To achieve this end, my research group is collecting IR reflectivity spectra and thin film data of about 100 minerals thought to be part of the condensation sequence, or identified in meteorites, and various simple chemical compounds, and glasses. Quantitative analyses of these data provide optical functions and emission spectra, which can be used to infer grain sizes, in addition to chemistry and structure. Application to the stars is made through collaborations with Angela Speck (University of Missouri) and Karly Pitman (PSI; NASA/JPL) Much of the laboratory data were gathered by Erin Keppel, a middle-school teacher in St. Louis, during her summer break. Future plans include low temperature emissions and reflection spectra, and study of organic compounds.