Late Heavy Bombardment
A number of issues have been raised regarding the connection between the Nice model and the Late Heavy Bombardment. Crater counts using topographic data from the Lunar Reconnaissance Orbiter find an excess of small craters relative to large impact-basins when compared to the size distribution of the asteroid belt. However, if the E-belt was the product of collisions among a small number of large asteroids, it may have had a size distribution that differed from that of the asteroid belt with a larger fraction of small bodies. A recent work has found that the bombardment originating from the inner band of asteroids would yield only two lunar basins and would be insufficient to explain ancient impact spherule beds. It suggests instead that debris from a massive impact was the source, noting that this would better match the size distribution of impact craters. A second work concurs, finding that the asteroid belt was probably not the source of the Late Heavy Bombardment. Noting the lack of direct evidence of cometary impactors, it proposes that leftover planetesimals were the source of most impacts and that Nice model instability may have occurred early. If a different crater scaling law is used, however, the Nice model is more likely to produce the impacts attributed to the Late Heavy bombardment and more recent impact craters.