Abstract:

Cataclysmic impact events represent the dominant, stochastic drivers shaping the fundamental composition, dynamics, and architecture of the Solar System. This comprehensive review synthesizes the evolution of planetary impact science, tracing the paradigm shift initiated by Eugene Shoemaker’s discovery of shocked quartz to the current era of high-fidelity numerical modeling. Planetary evolution is governed by two principal phases: the early Giant Impact Hypothesis (GIH) era and the later dynamical instability phase.

The GIH provides the necessary conditions to explain the major anomalies of the terrestrial planets:

1. Earth-Moon: The system’s high angular momentum and identical isotopic composition are reconciled by the rapid ‘immediate formation’ GI model, which suggests instantaneous satellite accretion involving substantial material from the proto-Earth.
2. Mercury: The planet’s disproportionately high mean density and large iron core fraction are the result of a massive, erosive impact that stripped a significant portion of its silicate mantle.
3. Mars: The stark hemispheric dichotomy (the Borealis Basin, potentially km in diameter) is attributed to a single, structure-defining mega-impact that established crustal thickness differences and potentially triggered early core dynamo activity.
4. Venus: The planet’s slow, retrograde spin and its lack of a natural satellite are consistent with a GI scenario that generated a minimal debris disk, preventing long-term satellite formation.

Later, the Solar System underwent the Late Heavy Bombardment (LHB), a discrete, intense spike in impact flux confirmed by lunar samples to have occurred between approximately and Ga. This bombardment was triggered by the Nice Model mechanism, where giant planet migration and orbital resonance scattered massive populations of planetesimals into the inner system. Finally, GI mechanics also define the outer system, explaining Uranus’s extreme axial tilt via a single oblique collision and the high-mass ratio binary formation of Pluto-Charon in the Kuiper Belt. Continued advancements in high-resolution Smoothed Particle Hydrodynamics (SPH) and cosmochronology remain crucial for constraining the precise conditions (merging, hit-and-run, erosion, disruption) that determined the final, unique characteristics of each planet.

Celestial Body	Basin/Crater Name	Diameter (km)	Relative Size (% of Body Dia.)	Significance
Mars	Borealis Basin?	8500?	125% (Estimated)	Hypothesized origin of the Martian Hemispheric Dichotomy.
Callisto	Valhalla	3000	62%	Classic multi-ring basin on a Jovian moon.
Moon	South Pole-Aitken (SPA)	2400	69%	Largest confirmed inner Solar System impact; LHB chronometer.
Mars	Hellas Planitia	2299	34%	Largest visible impact basin on Mars.
Mercury	Caloris Planitia	1300	27%	Largest preserved basin on Mercury.
Moon	Mare Imbrium	1146	33%	Major LHB-era basin.
Moon	Mare Orientale	930	27%	Multi-ring basin.
Iapetus (Saturn)	N/A	768	52%	Large impact structure.
Mercury	Rembrandt	716	15%	Large basin near Mercury’s south pole.
Moon	Mare Serenitatis	674	19%	Large, circular lunar mare.
Earth	Vredefort	300	2.4%	Largest confirmed terrestrial structure.
Venus	Mead	270	2.2%	Largest confirmed crater on Venus.