The Frequency of Binary Kuiper Belt Objects

Abstract

We estimate the frequency of widely spaced (separations greater than 0.5") Kuiper Belt binaries (KBBs) from surveys for new Kuiper Belt objects (KBOs) with the Deep Ecliptic Survey and through recovery observations for newly discovered KBOs at the Magellan telescopes. We find the frequency of KBBs versus discovery separation to be related by an inverse power law when combining our results with those for the fraction of close binaries (separations less than 0.5") found in the literature. For wide separations, our data and the resulting model agree with the model proposed by Goldreich et al. in 2002. However, including the frequency at the smallest separation rules out the semimajor-axis dependence of the Goldreich et al. model at the 99% confidence level, indicating that there is likely a turnover in the distribution at very close separations, or that the number of close binaries has been underestimated. In either case, the binary-frequency distribution favors binary formation models invoking gravitational rather than physical interactions-such as those proposed by Goldreich et al. and Astakhov et al. (2005).