Spectrophotometry of four Kuiper Belt objects with NICMOS

We have obtained spectrophotometric observations of four Kuiper Belt objects using the Hubble Space Telescope's Near Infrared Camera and Multi-Object Spectrometer, NICMOS, in broad and medium bandwidth filters selected to search for the presence of strong solid state spectral features in the 1.6-2.2 mu m range. We find distinct differences in the spectra of the four objects. The spectra of 1996 TQ(66), 1996 TP66, and 1996 TS66 are broadly similar: red optical colors and red neutral colors from 1.0 to 2.5 mu m. 1996 TS66 and 1996 TQ(66) show evidence of an absorption feature near 1.9 Irm. This feature is unidentified but is inconsistent with water ice. In sharp contrast, the reflectance of 1996 TO66 drops by more than a factor of 2 from 1 to 2 mu m and displays discrete features consistent with absorption by water ice, as reported by others. The surface composition of Kuiper Belt objects as revealed by infrared observations is considerably more complex than that suggested by the possible bimodal distribution of optical colors in these objects.