NEAR-INFRARED SPECTROSCOPY OF PRIMITIVE SOLAR-SYSTEM OBJECTS

We have obtained near-infrared (H and K band at lambda/DELTAlambda app roximately 480 to 600) spectra of a sample of primitive objects includ ing 2 Centaur objects (2060 Chiron and 5145 Pholus) and 16 P- and D-ty pe asteroids. The spectra were obtained at the United Kingdom Infrared Telescope using the cooled grating spectrometer CGS4, and were used t o search for chemically diagnostic vibrational features in these primi tive objects. Pholus exhibits broad adsorption features at 2.07 and 2. 27 mum, as well as a weak feature at 1.72 mum. The 1.72- and 2.27-mum features are similar to those seen in a laboratory tar sand sample. No distinct absorption features are found in other objects, including Ch iron, which displays a spectrally neutral continuum. A comparison of t he P- and D-type asteroid spectra with laboratory measurements of orga nic solids shows no compelling evidence for hydrocarbon overtones seen in terrestrial bituminous tar sands. (C) 1994 Academic Press, Inc.