Near-infrared observations of the outer Jovian satellites

On September 21, 1998, the outer jovian satellites Himalia (J6), Elara (J7) , Carme (J11), Pasiphae (J8), and Sinope (J9) were detected in the J, H, an d K, bandpasses in the course of the Two-Micron All Sky Survey. Similaritie s in near-infrared colors are consistent with the hypothesis that the outer satellites in prograde orbits are fragments of a captured C-type asteroid. The retrograde satellites in general exhibit considerable diversity. The n ondetection of retrograde Ananke is significant in that it requires visible to near-infrared reddening close to that of prograde Himalia and very diff erent from the other retrograde satellites. It is suggested that the retrog rade jovian satellites are fragments of a captured parent body more heterog eneous than the prograde parent. Alternatively, it is suggested that the re trograde satellites arose from more than one retrograde capture event and p ossible subsequent fragmentation. (C) 2000 Academic Press.