Formation of Binaries at a Stage of Rarefied Preplanetesimals

Introduction: Last years, new arguments in favor of the model of rarefied preplanetesimals-clumps were found (e.g., [1-3]). Even before new arguments in favor of formation of planetesimals from rarefied pre-planetesimals have been found, Ipatov [4-5] considered that some trans-Neptunian objects (TNOs), planetesi-mals, and asteroids with diameter d>100 km could be formed directly by the compression of large rarefied preplanetesimals, but not by the accretion of smaller solid planetesimals. Some smaller objects (TNOs, pla-netesimals, asteroids) could be debris of larger objects, and other smaller objects could be formed directly by compression of preplanetesimals. There are several hypotheses of formation of binaries for a model of solid objects (see e.g., [6-9]). Ipatov [5] supposed that a considerable fraction of trans-Neptunian binaries could be formed at the stage of compression of rarefied pre-planetesimals moved in almost circular orbits. For circular heliocentric orbits, two objects that entered inside the Hill sphere could move there for a longer time than those entered the sphere from eccentric heliocentric orbits. The diameters of preplanetesimals were greater than the diameters of solid planetesimals of the same masses. Therefore the models of binary formation due to the gravitational interactions or collisions of future binary components with an object (or objects) that were inside their Hill sphere, which were considered by several authors for solid objects, are more effective for rarefied preplanetesimals. Angular momentum of two collided rarefied preplanetesimals: Most of the papers devoted to the formation of spins of forming objects considered a model of solid-body accumulation. Besides such model , Ipatov [10-11] also studied formation of spins for a model of rarefied condensations. Formulas for the angular momentum of two collided rarefied pre-planetesimals-Hill spheres (with radii r 1 and r 2 and masses m 1 and m 2), moved in circular heliocentric orbits are presented in [11-12]. At a difference in their semimajor axes a equaled to Θ • (r 1 +r 2), the tangential velocity of collision is v τ =k Θ • (G • M S)