Could the lunar "Late heavy bombardment" have been triggered by the formation of Uranus and Neptune?

We investigate the hypothesis that the so-called Late Heavy Bombardment (LH B) of the Moon was triggered by the formation of Uranus and Neptune. As Ura nus and Neptune formed, which we assume occurred at the epoch of the LHB, t hey scattered neighboring icy planetesimals throughout the Solar System. So me of these objects hit the Moon. Our integrations show that the Moon would have accreted about 6 x 10(21) g, if we assume that the Uranus-Neptune reg ion initially contained 5 times the current mass of these planets in the fo rm of small solid objects. In addition, Mars would have accumulated similar to6 x 10(22) g of icy material, which could have supplied its putative ear ly massive atmosphere. However, Earth would likely have accreted only simil ar to7 x 10(22) g of water, or similar to5% of its oceans, through the mech anisms studied here. The numerical experiment that we have performed on the behavior of Uranus-Neptune planetesimals shows very good agreement with cu rrent constraints on the LHB. The influx of Uranus-Neptune planetesimals on to the Moon could have lasted for a time as short as 10 or 20 million years . The dynamical transport of the Uranus-Neptune planetesimals during this p rocess would have caused Jupiter and Saturn to migrate. This migration, in turn, would have destabilized objects in the jovian Trojan swarms and the a steroid belt. Thus, not only would Uranus and Neptune planetesimals have st ruck the Moon, but asteroids would have as well. We find that the Trojan as teroids of Jupiter could not have contributed a large percentage of materia l to the LHB, but the asteroid belt could, in principle, have contributed t o, or even dominated, the LHB, Although this model appears to explain the L HB well, it requires that fully formed Uranus and Neptune not appear in the trans-saturnian region until some 700 million years after the formation of the Earth. (C) 2001 Academic Press.