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"Animal, Vegetable or Mineral?
Playing Twenty Questions with Exoplanets."

#### Wren Montgomery

UC Berkeley, Dept. of Earth & Planetary Science

The effects of self compression on the internal structures of
planetary bodies are poorly understood. As the number of known planets
increases, understanding the effects of self-compression and layering on
mass and radius provides an estimate of planetary compositions, which is
useful data for the study of planetary system evolution. In this study,
we apply the second-order Birch-Murnaghan equation of state to a spherical
body, and study the effects of the material properties (as determined from
lab experiments) of the planet on astronomical observables, planetary
radius and mass. The most important parameter for a single-material,
single-phase body is the overall compression of the planet, i.e., the core
density over the surface density. For bodies of two or more distinct
layers, the location of the boundary, the ratio between the bulk moduli of
the two materials and the ratio between the initial densities of the
layers are also useful dimensionless parameters. The effects of these
parameters are most clearly seen in the resulting changes in the moment of
inertia coefficient, $\alpha$ = C/MR$^2$. Specific cases of astronomical
interest are discussed, including water planets and Earth-like rocky
planets with metallic cores.