Venus, often called Earth's twin due to its similar size and mass, lacks a moon—a puzzle that has long intrigued astronomers. While some have suggested a catastrophic collision destroyed it, a new study from the University of California, Riverside offers a gentler explanation: the planet may have slowly devoured its own moon. The research, led by astrophysicist Steven Kane, used computer simulations to show that Venus's extremely slow rotation—one full turn every 243 Earth days—combined with its gravity, would pull a moon inward rather than push it away, eventually causing it to fragment and be swallowed whole.
The simulations, which varied the moon's mass and orbital shape, consistently produced the same outcome: the moon spiraled inward and was destroyed. Only when the researchers artificially sped up Venus's rotation to once every 10 to 12 hours did a moon survive for billions of years, but that scenario is unrealistic given the planet's current sluggish spin. The findings contrast with Earth's situation, where our relatively fast 24-hour rotation pushes the moon outward at about 1.5 inches per year. As Kane noted, "Venus didn't require a catastrophe to arrive at what we can see today."
The study doesn't confirm that Venus ever had a moon, and finding physical evidence would be challenging since the planet's surface is geologically young, reshaped by volcanic activity. However, the research has broader implications: if a moon was absorbed, it could have dramatically altered Venus's rotation, geology, and climate, possibly affecting its habitability. This insight also offers a new lens for studying exoplanets—planets with slow rotations might be less likely to retain moons, which could influence their potential to support life. Kane emphasized that while a moon has benefits, it may not be essential for habitability, leaving the question open for future exploration.