3 Minutes
Venus shares size, mass and bulk composition with Earth, yet its environment is radically different: a dense CO2 atmosphere, surface temperatures hot enough to melt lead, sulfuric-acid clouds, a slow retrograde rotation, and no natural satellites. A new simulation study led by Mirco Bussmann at the University of Zurich tests whether a single, large collision with a Mars-sized body early in Venus’s history can account for both its unusual spin state and its lack of a moon.
Simulation methods and setup
Massive asteroid crashing into a planet - hideto999/Shutterstock
The research team used Smooth Particle Hydrodynamics (SPH), a numerical method that models planets as collections of particles carrying physical properties. Their Venus analogue consisted of an iron core (~30% by mass) and a silicate mantle (~70%). Impactors ranged from 0.01 to 0.1 Earth masses (up to roughly Mars size) and approached at 10–15 km/s. The simulations explored a matrix of impact angles, speeds, and initial Venus rotation and thermal states to measure two outcomes: changes in rotation period and the amount of debris placed into orbit (a circumplanetary disk capable of forming a moon).
Key simulation parameters
- Interior structure: iron core ~30% / silicate mantle ~70%
- Impactor masses: 0.01–0.1 Earth masses
- Impact velocities: 10–15 km/s
- Varied impact angle and initial planetary spin/thermal profile
Key results and implications
Across a wide set of scenarios, single large impacts can (a) reverse or dramatically slow Venus’s spin to produce its present retrograde, very long day, and (b) typically fail to leave a substantial circumplanetary debris disk. Most collision debris either falls back into the atmosphere or re‑accretes onto the planet, preventing the stable satellite formation that produced Earth’s Moon. The study also finds that such an impact would deposit vast amounts of heat into Venus’s mantle, disrupting mantle convection and likely suppressing plate tectonics for long timescales. This thermal reset provides a plausible mechanism for the planet‑wide volcanic resurfacing that explains Venus’s relatively young-looking surface and low crater count.
Lead author Mirco Bussmann and colleagues emphasise that a single Mars‑sized collision is not the only possible explanation, but their models show it is a robust, self‑consistent scenario that links Venus’s rotation, satellite absence, and geological evolution.
Conclusion
SPH simulations from the University of Zurich demonstrate that a Mars‑sized impact early in Venus’s history can simultaneously explain the planet’s slow retrograde rotation, its lack of a moon, and its global volcanic resurfacing. The results strengthen the case that giant collisions shaped the divergent evolutionary paths of Earth and Venus and highlight how impact dynamics, planetary interior response, and orbital debris production interplay to determine a planet’s long‑term geology and satellite system.
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