This result was most frequent if Planet V's mass was less than 0.25 of Mars. The other simulations were not considered successful because Planet V either survived for the entire 1 billion year length of the simulations, or collisions occurred between planets. The terrestrial Planet V hypothesis was later examined by Ramon Brasser and Alessandro Morbidelli. Their work was the first to focus on the magnitude of the bombardment caused by Planet V. Brasser and Morbidelli calculated that to create the Late Heavy Bombardment Planet V would have to remove 95% of the pre-LHB main asteroid belt or 98% of the inner asteroid belt (semi-major axis < 2.5 AU). Depleting the main asteroid belt by 95% with a 0.5 Mars-mass Planet V was found to require it remain in an orbit crossing the entire asteroid belt for 300 million years. This orbital evolution was not observed in any simulations; Planet V typically entered an Earth-crossing orbit resulting in a short dynamic lifetime before entering such an orbit. In a few percent of simulations Planet V remained in the inner belt long enough to produce the LHB. However, producing the LHB from the inner asteroid belt would require the inner asteroid belt to have begun with 4–13 times the mass, and 10-24 time the orbital density, as the rest of the asteroid belt. Brasser and Morbidelli also examined the hypothesis that Planet V caused the LHB by disrupting putative asteroid belts between the terrestrial planets. The authors noted that the lack of present-day detection of the remnants of these belts places a significant constraint on this hypothesis, requiring that they be 99.99% depleted before Planet V was lost. While this occurred in 66% of the simulations compatible with the current Solar System for a Venus-Earth belt, it did not occur in any for the Earth-Mars belt due to its higher stability. Morbidelli and Brasser concluded from this result that an Earth-Mars belt could not have contained a significant population. Although Planet V could generate a Late Heavy Bombardment by disrupting a massive Venus-Earth belt alone, the authors observed that significant differences in these belts has not been produced in planetary formation models. An impact of Planet V onto Mars, forming the Borealis Basin has recently been proposed as an explanation for the Late Heavy Bombardment. Debris from this impact would have a different size distribution than the asteroid belt with a smaller fraction of large bodies and would result in a lower number of giant impact basins relative to craters.