Institute of Astronomy

Improving our knowledge of exoplanetary interiors through a refined water equation of state

SpeakerTalk DateTalk Series
Scott Thomas28 July 2014Across HR 2014 Posters


We have entered an era where planets at smaller and smaller radii are able to be found and characterized. A growing area of interest is exoplanetary interior modeling: using mass and radius measurements, these models allow us to place constraints on the planets' interior compositions. One important piece of information required for interior models is the pressure-temperature-density relation of various minerals, or ""equation of state"". Most authors use simple equations of state, often based on extrapolations of low-pressure experimental data. This is driven partially by the lack of available experimental information and partially by the desire to simplify the models, so this approach often neglects temperature dependence. While this produces only small changes in the bulk parameters of the system, more accurate equations of state are important when we build thermal structure models to understand the thermal evolution of planets. This is especially relevant for planets containing large fractions of water, which has a rich phase structure with strong temperature dependence. We survey the H2O equations of state used in exoplanetary interior studies to date, and compile a fully temperature-dependent H2O equation of state in the region relevant to planetary interior pressures and temperatures. We include data from a variety of sources, including experimental measurements for familiar phases like vapour, liquid and low-pressure ice; experimentally-verified quantum molecular dynamics simulations; and theoretical calculations at extreme temperatures. Using this, we examine the internal structure and evolution of planets containing H2O, including the effects of irradiation during their evolution and possible migration.