On the Eccentricity of Proxima b

Abstract

We apply Monte Carlo projection to the radial-velocity data set that Anglada-Escudé et al. use for the discovery of Proxima b. They find an upper limit to the orbital eccentricity of ε < 0.35. To investigate the eccentricity issue further, we calculate a suite of mono- and bi-variate densities of ε . After discarding apparent artifacts at ε ≈ 0 and ε ≈ 1, we find that ε seems to have a tri-modal sampling distribution—three chimeras or types of orbit compatible with the RV data set. The three modes (peaks) in the density of ε are located at ε  = {0.25, 0.75, 0.95}, with relative weights {0.79, 0.10, 0.11}. Future RV observations will clarify which of the three chimeras represents the true eccentricity of Proxima b. The most likely estimate is ε est  = 0.25, and our lower limit is ε l lim  = 0.025. Our strategic, long-term goal is to elevate the orbital analyses of exoplanets to meet the challenges of sometimes complex probability density distributions.