Formation and Migration of Trans-Neptunian Objects
  Trans-Neptunian objects (TNOs) with diameter d>100 km moving now in not very eccentric orbits could be formed directly by the compression of large rarefied dust condensations (with semi-major axes a>30 AU), but not by the accretion of smaller solid planetesimals. A considerable portion of TNO binaries could be formed at the stage of compression of condensations. Five years before the first TNO was observed, we supposed that, besides TNOs formed beyond 30 AU and moving in low eccentric orbits, there were former planetesimals from the zone of the giant planets in highly eccentric orbits beyond Neptune. For the present mass of the trans-Neptunian belt, the collisional lifetime of 1-km TNO is about the age of the solar system. At the present time TNOs can supply a large amount of matter to the near-Earth space. 
S. I. Ipatov