Billions of Years Ago, Venus May Have Had a Moon—Which the Planet Promptly Gobbled Up, Study Suggests

Scientists have puzzled over why the planet dubbed “Earth’s twin” doesn’t have a moon. Computer simulations hint that if Venus ever did have one, it probably would’ve cannibalized its companion

Margherita Bassi | Daily Correspondent

September 17, 2026 11:00 a.m.

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Earth’s next-door neighbor Venus is often called our twin. The two planets feature similar sizes, masses and structures. One glaring difference between these siblings, however, is that Venus lacks a moon.

Scientists suspect it once had one, since space rocks pelted the planet during the solar system’s youth some 4.5 billion years ago. That’s the leading theory behind how Earth’s moon was born—it formed from debris kicked up by a celestial collision. But some think the second planet from the sun lost its hypothetical satellite in a subsequent crash; another incoming rock may have destroyed it.  

Now, a team of researchers is proposing a new idea: If Venus ever had a moon, the planet would have promptly gobbled it up. They published their work September 14 in the Astrophysical Journal.

“If ​it had a moon—and it likely did at some point—it could not have kept it,” study co-author Stephen Kane, a planetary scientist at the University of California, Riverside, tells Reuters’ Steve Gorman. “That moon would have crashed down on the planet in a relatively short time ​scale.”

Every year, Earth’s moon moves approximately 1.6 inches away from us. The growing distance is caused by our planet’s relatively fast rotation, whose energy pushes the moon away. By contrast, Venus spins very slowly; one Venus day is 243 Earth days long. Kane and his colleagues suspected that Venus’ slow spin and gravity could pull a moon inward toward the planet and to its eventual death.

The team put this hypothesis to the test with computer simulations, building models based on the physics of how planetary bodies interact through gravity. The researchers initially simulated the evolution of Earth and our moon to confirm that their models could correctly represent a well-understood system.

They then tested what could’ve happened with Venus, inputting different planet rotational speeds as well as variously sized hypothetical moons—from half the mass of Earth’s moon to ten times as massive. In most scenarios, the moon smashed into Venus.

One of the models predicted that a hypothetical Venusian moon at least twice as massive as Earth’s natural satellite could’ve lasted between 30 million and 1.7 billion years. Overall, the simulations indicated that the more massive the moon, the faster it met its death.

On the other hand, both models suggested that if Venus had a moon less massive than Earth’s, it could have survived to today—if the planet was spinning fast enough. Specifically, Venus would have needed “a day shorter than about 12 hours” when the satellite formed, Kane tells Space.com’s Robert Lea.

However, the conditions prime for Venusian moon survival “don’t match what we think early Venus was actually like,” he notes.

The study doesn’t prove that Venus once had a moon. Rather, it suggests that if one ever existed, it wouldn’t have stuck around for long.

Still, that’s difficult to verify, Paul Byrne, a planetary geologist at Washington University in St. Louis who did not participate in the study, tells New Scientist’s Jonathan O’Callaghan. “It’s exceedingly hard to test this idea because there is basically nothing left behind” on Venus’ surface, which has been remade through volcanic activity.

Kane agrees it’s a challenging undertaking. “Finding direct observational evidence is pretty tough,” he tells Space.com, but argues indirect strategies are available. If debris from a smashed moon ended up on Venus, it may have left chemical traces in its surface or atmosphere, he notes.

Evidence might also be hiding beneath Venus’ surface, according to a statement. On Earth, for example, seismic studies have found structures deep within the planet that might be leftovers from the smashup that made our moon. Researchers could attempt similar measurements on Venus.

The findings have implications for whether the planet once had the conditions to host life. Some scientists think that long ago, Venus had liquid water on its surface—a feature thought to be crucial for life as we know it. If the planet historically had a large moon, the satellite’s gravitational influence on the ocean could have helped make the planet habitable. Its destruction, however, could have delivered an energy punch that evaporated much of the planet’s water and caused a runaway greenhouse effect—an intense, unstoppable warming cycle—that created the thick, inhospitable atmosphere on Venus today.

If the planet feasted on its own moon, “it could definitely be connected to Venus’ runaway greenhouse state,” Kane tells New Scientist.

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.