Recent studies regarding the habitability, observability, and possible orbital evolution of the indirectly detected exoplanet Proxima b have mostly assumed a planet with $M \sim 1.3$ $M_\oplus$, a rocky composition, and an Earth-like atmosphere or none at all. In order to assess these assumptions, we use previous studies of the radii, masses, and compositions of super-Earth exoplanets to probabilistically constrain the mass and radius of Proxima b, assuming an isotropic inclination probability distribution. We find it is ~90% likely that the planet's density is consistent with a rocky composition; conversely, it is at least 10% likely that the planet has a significant amount of ice or an H/He envelope. If the planet does have a rocky composition, then we find expectation values and 95% confidence intervals of $\left<M\right>_\text{ rocky} = 1.63_{ -0.72}^{ +1.66}$ $M_\oplus$ for its mass and $\left<R\right>_\text{ rocky} = 1.07_{ -0.31}^{ +0.38}$ $R_\oplus$ for its radius.
Categories: astro-ph.EP