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 1.54 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 material. Comparisons of Nereid's spectrum with those of other objects such as the Centaurs 1997 CU(26), and 5145 Pholus, and Neptune's largest regular satellite 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.