Formation and Migration of Trans-Neptunian Objects - Proceedings of the   conference "Scientific Frontiers in Research of Extrasolar Planets"
  Some large trans-Neptunian objects could be formed by the compression of rarefied dust condensations, but not by the accumulation of smaller planetesimals. A considerable portion of near-Earth objects could have come from the trans-Neptunian region. Our runs of the evolution of thousands orbits of Jupiter-family comets under the gravitational influence of planets showed that former Jupiter-family comets collide with the terrestrial planets mostly from orbits with aphelia located deep inside Jupiter's orbit. 
S.I. Ipatov