Blue Coma and Red Surface of 174P/Echeclus: Two Sides of the Same Coin?

Seccull et al. (2019) report a dramatic difference in the color of the coma and surface of Centaur 174P/Echeclus. While the coma was blue in appearance, the surface was red. A similar phenomenon was found in laboratory optical measurements of single-scattering feldspar particles and of a surface comprised of these same particles. Thus, the observations do not necessarily suggest different chemical composition and size distribution of dust in the coma and surface of 174P/Echeclus. Instead, the observed difference could arise from multiple-scattering phenomena that makes a significant contribution to light scattering by a regolith, but does not appear in an optically thin coma.