Water ice on Nereid

A near-infrared spectrum of Neptune's satellite Nereid was obtained at the Keck Observatory on 1997 May 1. The spectrum shows two absorptions near 1.5 4 and 2.03 mu m and is well matched by a synthetic spectrum of an intimate mix of low-temperature, particulate water ice and dark, blue-colored materi al. Comparisons of Nereid's spectrum with those of other objects such as th e Centaurs 1997 CU26, and 5145 Pholus, and Neptune's largest regular satell ite Proteus, admit the possibility that Nereid Is a primordial satellite of Neptune (and perhaps its only remaining one) rather than a captured object , but more data are needed to rule out one scenario or the other. (C) 1999 Academic Press.