A deeper look at the colors of the saturnian irregular satellites

Abstract

We have performed broadband color photometry of the twelve brightest irregular satellites of Saturn with the goal of understanding their surface composition, as well as their physical relationship. We find that the satellites have a wide variety of different surface colors, from the negative spectral slopes of the two retrograde satellites S IX Phoebe ( S ′ = − 2.5 ± 0.4 ) and S XXV Mundilfari ( S ′ = − 5.0 ± 1.9 ) to the fairly red slope of S XXII Ijiraq ( S ′ = 19.5 ± 0.9 ). We further find that there exist a correlation between dynamical families and spectral slope, with the prograde clusters, the Gallic and Inuit, showing tight clustering in colors among most of their members. The retrograde objects are dynamically and physically more dispersed, but some internal structure is apparent.