Formation of Kuiper-belt binaries through multiple chaotic scattering encounters with low-m.pdf

a r X i v : a s t r o - p h / 0 5 0 4 0 6 0 v 1 4 A p r 2 0 0 5 Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 2 February 2008 (MN LATEX style file v2.2) Formation of Kuiper-belt binaries through multiple chaotic scattering encounters with low-mass intruders Sergey A. Astakhov,1? Ernestine A. Lee 2,3? and David Farrelly2? 1John von Neumann Institute for Computing, Forschungszentrum Ju?lich, D-52425 Ju?lich, Germany 2Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322-0300, USA 3FivePrime Therapeutics, 951 Gateway Boulevard, South San Francisco, CA 94080, USA Submitted 2004 November 7; Accepted 2005 April 4 ABSTRACT The discovery that many trans-neptunian objects exist in pairs, or binaries, is proving invaluable for shedding light on the formation, evolution and structure of the outer Solar system. Based on recent systematic searches it has been estimated that up to 10% of Kuiper-belt objects might be binaries. However, all examples discovered to- date are unusual, as compared to near-Earth and main-belt asteroid binaries, for their mass ratios of order unity and their large, eccentric orbits. In this article we propose a common dynamical origin for these compositional and orbital properties based on four- body simulations in the Hill approximation. Our calculations suggest that binaries are produced through the following chain of events: initially, long-lived quasi-bound bina- ries form by two bodies getting entangled in thin layers of dynamical chaos produced by solar tides within the Hill sphere. Next, energy transfer through gravitational scat- tering with a low-mass intruder nudges the binary into a nearby non-chaotic, stable zone of phase space. Finally, the binary hardens (loses energy) through a series of rela- tively gentle gravitational scattering encounters with further intruders. This produces binary orbits that are well fitted by Kepler ellipses. Dynamically, the overall process is strongly favored if the origina