Moon-Sized Impact May Have Caused Venus' Strange Rotation

Planetary scientists suggest a high-velocity collision with a moon-sized object likely caused the slow retrograde rotation of Venus ^[1].

This finding addresses a long-standing puzzle in planetary science regarding why Venus rotates in the opposite direction of most planets in the solar system. Understanding this event provides critical insight into the early history of the inner solar system and the violent processes that shape planetary evolution.

The research was presented this month at the European Geosciences Union General Assembly in Vienna ^[2]. According to the simulations, the impactor was approximately one-tenth the mass of Venus ^[2]. This massive object struck the planet at a high angle and high velocity, providing the necessary force to flip or slow the planet's axial spin.

The energy released during this collision was immense. The study indicates that the impact would have melted nearly the entire mantle of the planet ^[1]. This level of thermal disruption suggests a catastrophic event that fundamentally reset the geological and rotational state of Venus.

While other theories have attempted to explain the retrograde rotation, these new simulations offer a mechanical explanation based on orbital dynamics and impact physics. The researchers used these models to demonstrate how a specific combination of mass, velocity, and angle could result in the current observed rotation of the planet ^[1].

The presentation in Vienna highlights the ongoing effort to map the chaotic early years of the solar system. By recreating the collision, scientists can better understand how stochastic events, rather than steady evolution, can dictate the characteristics of a planet ^[3].