Characterizing Io's Pele, Tvashtar and Pillan plumes: Lessons learned from Hubble

► Absorption and reflection properties of gas and dust in Io's plumes are analyzed. ► The 0.26-0.33 μm brightness of Io's plumes is not matched by Rayleigh scattering. ► The detected dust particle size is comparable for all of Io's active plume types. ► Thus, Io's Pele-type plumes are faint because of low dust mass, not particle size. ► Io's Prometheus-type plumes release the highest SO2 gas densities, ∼1017-1018 cm−2.