Near-Infrared Spectroscopy of Centaurs and Irregular Satellites

We have obtained near-infrared spectra of the four brightest known Centaurs and of five irregular satellites of giant planets. Many of these objects show 1.5 and 2.0 μm absorption bands indicative of water ice, including 1997 CU_(26), Pholus, Phoebe (S9), and Nereid (N2). The satellites of Jupiter—Elara, Himalia, and Pasaphae (J6, J7, J8)—appear spectrally featureless, consistent with asteroidal origins for these bodies. Phoebe's surface water ice indicates that it formed as an icy planetesimal rather than as an asteroid.

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