Reassessing late-stage impact assumptions in light of modern planet formation paradigms

In this Perspective, we examine the implications of modern cold-accretion and disk-mediated paradigms for two widely cited impact hypotheses: the Moon-forming giant impact and the Late Heavy Bombardment, with attention to consequences for planetary thermal histories and early habitability. Rather than seeking to invalidate these hypotheses, we aim to assess the extent to which their underlying assumptions remain compatible with evolving formation paradigms. Particular attention is given to the consequences for planetary thermal histories, crustal stability, volatile retention, and early habitability. We further outline observational and theoretical constraints that may help distinguish between competing formation–impact scenarios as planetary science continues to develop.