= Exoplanet bulk-composition ternary diagram
An <exoplanet bulk-composition ternary diagram> represents three component <mass fractions> by one point inside a triangle. If the components have fractions $x_1,x_2,x_3$, then $x_i\geq0$ and $x_1+x_2+x_3=1$. Each vertex is a pure component, an edge excludes the opposite component, and the centre corresponds to equal thirds. The fractions are <barycentric coordinates> relative to the vertices.
For an illustrative iron-rock-water model, measured <mass> and <radius> restrict the allowed part of the triangle through an <exoplanet interior> calculation. They need not select a unique point, making <exoplanet interior-composition degeneracy> visible. The diagram is conditional on the chosen three components: an unmodelled <hydrogen>-<helium> envelope cannot automatically be interpreted as more of one of those solid components.
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