Satellites of the Largest Kuiper Belt Objects

We have searched the four brightest objects in the Kuiper belt for thepresence of satellites using the newly commissioned Keck Observatory LaserGuide Star Adaptive Optics system. Satellites are seen around three of the fourobjects: Pluto (whose satellite Charon is well-known), 2003 EL61, and 2003UB313. The object 2005 FY9, the brightest Kuiper belt object after Pluto, doesnot have a satellite detectable within 0.4 arcseconds with a brightness of morethan 0.5% of the primary. The presence of satellites to 3 of the 4 brightestKuiper belt objects is inconsistent with the fraction of satellites in theKuiper belt at large at the 99.1% confidence level, suggesting a differentformation mechanism for these largest KBO satellites. The satellites of 2003EL61 and 2003 UB313, with fractional brightnesses of 5% and 2% of theirprimaries, respectively, are significantly fainter relative to their primariesthan other known Kuiper belt object satellites, again pointing to possibledifferences in their origin