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Abstract: A large fraction of 100-km-class low-inclination objects in the classicalKuiper Belt KB are binaries with comparable mass and wide separation ofcomponents. A favored model for their formation was capture during thecoagulation growth of bodies in the early KB. Instead, recent studies suggestedthat large objects can rapidly form in the protoplanetary disks when swarms oflocally concentrated solids collapse under their own gravity. Here we examinethe possibility that KB binaries formed during gravitational collapse when theexcess of angular momentum prevented the agglomeration of available mass into asolitary object. We find that this new mechanism provides a robust path towardthe formation of KB binaries with observed properties, and can explain widesystems such as 2001 QW322 and multiples such as 47171 1999 TC36. Notably,the gravitational collapse is capable of producing 100% binary fraction for awide range of the swarm-s initial angular momentum values. The binarycomponents have similar masses 80% have the secondary-over-primary radiusratio >0.7 and their separation ranges from ~1,000 to ~100,000 km. The binaryorbits have eccentricities from e=0 to ~1, with the majority having e<0.6. Thebinary orbit inclinations with respect to the initial angular momentum of theswarm range from i=0 to ~90 deg, with most cases having i<50 deg. Our binaryformation mechanism implies that the primary and secondary components in eachbinary pair should have identical bulk composition, which is consistent withthe current photometric data. We discuss the applicability of our results tothe Pluto-Charon, Orcus-Vanth, 617 Patroclus-Menoetius and 90 Antiopebinary systems.

Autor: David Nesvorny, Andrew N. Youdin, Derek C. Richardson


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