  The formation of trans-Neptunian satellite systems at the stage of rarefied
preplanetesimals (i.e., condensations of dust and/or objects less than 1 m in
diameter) is discussed. It is assumed that trans-Neptunian objects (including
those with satellites) could form as a result of compression of parental
rarefied preplanetesimals. The formulas for calculating the angular momentum of
two colliding condensations with respect to their center of mass, which were
applied earlier in (Ipatov, 2010) in the comparison of such momenta with the
angular momenta of observed satellite systems, are used to estimate the angular
momenta of condensations needed to form satellite systems. It is demonstrated
that the angular velocities of condensations used in (Nesvorny et al., 2010) as
the initial data in the computer simulation of compression of rarefied
preplanetesimals and subsequent formation of trans-Neptunian satellite systems
may be obtained in collisions of preplanetesimals with their radii comparable
to the corresponding Hill radii. For example, these angular velocities are in
the range of possible values of angular velocities of a parental rarefied
preplanetesimal formed as a result of a merger of two colliding rarefied
preplanetesimals that moved in circular heliocentric orbits before a collision.
Some rarefied preplanetesimals formed as a result of collision of
preplanetesimals in the region of formation of solid small bodies acquire such
angular momenta that are sufficient to form satellite systems of small bodies.
It is likely that the ratio of the number of rarefied preplanetesimals with
such angular momenta to the total number of rarefied preplanetesimals producing
classical trans-Neptunian objects with diameters larger than 100 km was 0.45
(the initial fraction of satellite systems among all classical trans-Neptunian
objects).
