Colors and Spectra of Kuiper Belt Objects^*

We present new measurements of the optical colors of Kuiper belt objects, principally from the Keck 10 m telescope. The measurements confirm the existence of a wide spread in the B-V, V-R, and R-I color indices as we found previously. Relative to the sun, the Kuiper belt objects exhibit reflected colors from nearly neutral to very red. The optical and optical-infrared (V-J) color indices are mutually correlated, showing the presence of a single reddening agent from 0.45 to 1.2 μm. On the other hand, we find no evidence for linear correlations between the color and absolute magnitude (a proxy for size), instantaneous heliocentric distance, semimajor axis, or with any other orbital property. In this regard, the Kuiper belt objects differ from the main-belt asteroids, in which strong radial color gradients exist. We find no statistically significant evidence for bimodal or other nonuniform color distributions, either in our data or in data previously reported to show such evidence. The impact resurfacing hypothesis is reexamined in the light of the new color data and is rejected as the primary cause of the observed color dispersion. We also present new near-infrared reflection spectra of 1993 SC, 1996 TS₆₆, 1999 DE₉ and 2000 EB₁₇₃, taken at the Keck and Subaru telescopes. These spectra, combined with others from the published literature, provide independent evidence for compositional diversity in the Kuiper belt. Objects 2000 EB₁₇₃, 1993 SC, and 1996 TS₆₆ are spectrally bland, while 1999 DE₉ shows solid-state absorption bands.