The Lunar Late Heavy Bombardment
- There is a controversy of whether the lunar basin forming impacts 3.9Gyr ago were:
- The tail end of accretion. However, Morbidelli et al (2001) show impactors don't last 700Myrs.
- A spike in the impact rate. Some (controversial) evidence for this (Cohen et al. 2000):
- If a spike, the most likely cause is a change in the dynamical state of the planetary system.
LHB constraints (stolen from C. Koeberl's web site)