A new study published in The Astrophysical Journal proposes that Venus, Earth’s planetary twin, may have once had a moon that was ultimately consumed by the planet’s gravity. Led by University of California, Riverside (UCR) astrophysicist Stephen Kane, the research challenges earlier theories that Venus’s lack of a moon resulted from a catastrophic collision or an absence of moon-forming events. Instead, Kane’s work suggests that Venus’s extremely slow rotation—243 Earth days per revolution—would have caused any hypothetical moon to spiral inward and be destroyed.
Venus May Have Swallowed Its Moon, Study Suggests
How Venus’s Slow Spin Doomed a Moon
Kane’s computer models simulate the gravitational interactions between Venus and a potential moon. The study highlights that Earth’s moon moves away from the planet due to tidal forces transferring energy from Earth’s rotation to the moon’s orbit. In contrast, Venus’s sluggish spin creates the opposite effect: tidal forces would have drawn a moon closer until it crossed the Roche limit, the distance at which a planet’s gravity overcomes a moon’s structural integrity.
This means that Venus’s lack of a moon may be a natural outcome of ordinary tidal physics,
Kane said. The Roche limit for Venus is calculated at about 2.85 Venus radii, or roughly 17,000 kilometers from the planet’s center. Any moon crossing this threshold would disintegrate, potentially forming a ring system before debris rained onto Venus’s surface.
Implications for Venus’s Evolution
The study raises questions about Venus’s geological and climatic history. If a moon existed, its destruction could have altered the planet’s rotation, geology, and atmosphere. Such an event might have influenced whether Venus ever harbored conditions suitable for life. NASA climate models suggest early Venus could have been temperate with liquid water, but a moon’s destruction might have accelerated its transformation into the hellish world it is today.
Unanswered Questions and Future Research
The study does not confirm that Venus ever had a moon but provides a framework for testing the theory. Scientists could search for geological or atmospheric signatures of a past moon, such as unusual noble gas abundances or isotopic ratios. Future NASA missions, including the DAVINCI+ and VERITAS probes, aim to study Venus’s atmosphere and geology, potentially uncovering clues about its history.
The implications extend beyond Venus,
Kane said. Understanding how planetary rotation and tidal forces shape moon systems could inform studies of exoplanets and their potential habitability. For now, the idea that Venus may have “swallowed” its moon remains a compelling explanation for one of the solar system’s enduring mysteries.