Venus’s Missing Moon: New Study Suggests Tidal Decay, Not Catastrophe, Took It

Venus shares Earth’s mass, size, and internal structure, leading astronomers to expect a natural satellite. Yet the planet has none. Earlier explanations ranged from a moon never forming to a violent impact that shattered an existing satellite. The latest research from the University of California, Riverside, offers a different scenario: a slow inward spiral driven by Venus’s own gravity and rotation.

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Venus rotates once every 243 Earth days, the longest rotation period of any planet in the solar system and longer than its orbital year. This sluggish spin creates a tidal environment opposite to Earth’s. On Earth, a 24-hour day causes the Moon to recede at roughly 1.5 inches per year. By contrast, Venus’s protracted rotation would generate a tidal bulge that lags behind a nearby moon, exerting a drag that pulls the satellite inward. Over time, the moon would experience increasing tidal stress, fragment, and ultimately be absorbed by the planet. The study argues that this gradual process eliminates the need for an external catastrophe to explain the current lack of a Venusian moon.

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The researchers presented the hypothesis in a press release, noting that the model aligns with known tidal-interaction physics and does not require a massive impact event. No competing hypotheses were presented in the release, and the authors did not claim definitive proof, describing the scenario as a plausible explanation pending further investigation.

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• “Venus didn’t require a catastrophe to arrive at what we can see today,” — Steven Kane, an astrophysicist and the paper’s lead author

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