Colors of Faint Jovian and Saturnian Irregular Moons

Abstract Jupiter and Saturn are encircled by irregular moons that are in orbital groupings. Groups are postulated to be fragments of some parent object—this hypothesis can be probed by studying the moons’ surface properties via their optical colors, which correlate within the orbital families. We used the Caltech HIgh-speed Multi-color camERA (CHIMERA) camera on the Palomar Hale telescope to obtain simultaneous Sloan Digital Sky Survey (SDSS) g - and r -band photometry for a small set of interesting Jovian and Saturnian irregulars. We find colors consistent with literature values for the bright moons Siarnaq and Ananke. Our measurements of the fainter moons Praxidike (Jovian Ananke group) and Saturn’s Mundilfari also match prior measurements. We find Thrymr in Saturn’s Phoebe group to be red, providing additional constraints to two strongly discrepant literature colors. We report g measurements of Kallichore, a potential ESA JUpiter ICy moons Explorer (JUICE) flyby target.