Ternary plot for Kepler-102d (K-102d) showing the range of possible combinations of iron, rock, and ice in increments of 10% for a planet of fixed radius. The color bar shows the resulting mass of such a planet. Masses and volumes of different substances are calculated by solving equations of state (EOS) using assumed internal pressure and temperatures using Burnman 0.9 (Cottaar et al. 2016). Every point corresponds to a planet with physically allowed EOS for that combination of iron, rock, and ice—and all produce values for the mass of the planet within 1σ (large points) and 2σ (small points) of our measured mass value for that planet. The horizontal dotted lines show iron fraction, the dotted lines with negative slope show ice fraction, and the lines with positive slope show silicate fraction. The red circle highlights the composition that produces our best-fit mass of M _d = 2.5 M _⊕.