A comparison of the median masses and errors for each of the GJ 9827 planets (filled squares), as determined from the MCMC error estimation in SYSTEMIC (top, with upper limits for planet c and d) and in RADVEL (bottom), vs. other small exoplanets (filled circles) with mass and radius uncertainties ≤1.9 M_⊕ and <1 R_⊕, respectively, from the NASA Exoplanet Archive. The point color corresponds to the planet’s insolation flux. Over-plotted in colored solid and dashed lines are planet composition estimates from Zeng et al. (2016). From top to bottom, the compositions are 100% Fe (solid red), sizes/masses of planets that result from the maximum collisional mantle stripping (solid gray, extrapolated from Marcus et al. 2010), 50% Fe (dashed orange), 25% Fe (dashed yellow), MgSiO₃ (rocky, solid green), 25% H₂O (dashed cyan), 50% H₂O (dashed blue), 100% H₂O (solid light purple), and cold H₂/He (solid dark purple).