A Southwest Research Institute (SwRI)-led study has revealed striking differences in the early impact histories of Venus and Earth. Venus endured more violent, high-energy collisions that superheated its core—a critical factor that may explain its prolonged volcanic activity and geologically youthful surface compared to Earth.

In collaboration with Yale University, SwRI scientists synthesized decades of planetary research into a comprehensive Nature Reviews paper examining how late accretion — the final stage of planetary growth — dictates the long-term evolution of rocky worlds. This process, accounting for just 1% of a planet’s mass, plays an outsized role in determining planetary characteristics, from geophysical properties to potential habitability.

Terrestrial planets like Mercury, Venus, Earth, and Mars emerged from the dusty disk surrounding young Sun. As gravity assembled smaller bodies into planetesimals and protoplanets, late-stage collisions delivered transformative impacts. Earth, likely the last to form, achieved 99% of its current mass within 60–100 million years after the first solid materials condensed in the early Solar System.

The study highlights how impactors don’t just leave craters—they alter a planet’s very chemistry. “We track siderophile (metal-loving) elements in planetary crusts and mantles like forensic evidence,” Marchi explained. “Their distribution reveals the timing of core formation and subsequent bombardment.”

As astronomers discover thousands of exoplanets, Marchi’s team suggests impact history should be a key habitability filter:
– Collisions govern atmospheric development through volatile delivery/erosion;
– Plate tectonics—critical for climate regulation—may require specific impact conditions.

While Earth’s active geology has erased much impact evidence, lunar craters serve as a time capsule. By combining lunar data with dynamical models, researchers are reconstructing our solar system’s violent youth — a template for understanding exoplanetary systems. This work underscores how random cosmic violence ultimately determined which worlds became hellish like Venus, arid like Mars, or habitable like Earth.

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