High-Precision Photometry of Extreme Kbo 2003 El61

We present high-precision, time-resolved, visible and near-infrared photometry of the large (diameter ∼ 2500 km) Kuiper belt object (136108) 2003 EL 61 . The new data confirm rapid rotation at period P = 3.9155 ± 0.0001 h with a peak-to-peak photometric range of Δ m R = 0.29 ± 0.02 mag and further show subtle but reproducible color variations with rotation. Rotational deformation of 2003 EL 61 alone would give rise to a symmetric light curve free of color variations. The observed photometric deviations from the best-fit equilibrium model show the existence of a large surface region with an albedo and color different from the mean surface of 2003 EL 61 . We explore constraints on the nature of this anomalous region set by the existing data.