Venus May Have Eaten Its Own Moon

A moon may once have circled Venus. Past tense. Then Venus got hungry.

A team from the University of California, Riverside and the University of Bordeaux modeled a young Venus with a hypothetical moon. They concluded that an early moon, later consumed by the planet, is plausible. The paper, submitted to the preprint site arXiv on Sept. 2, has not been peer reviewed.

Here is how that would have played out across geologic time. Any such moon would have formed early in the solar system's history. If it survived close to 2 billion years, the planet has been moonless for roughly the past 2.5 billion. How long it lasted comes down to mass. A moon half as massive as ours could have held on for some 1.7 billion years. Double that mass and it would have been gone in around 30 million.

The mechanism is a slow-motion trap. Venus spins more slowly than Earth, so a moon would have handed its angular momentum to the planet and spiraled inward, the reverse of Earth's slowly retreating moon. Roughly 9,321 miles (15,000 kilometers) above Venus it would have hit the Roche limit, the point where the planet's gravity tears a moon apart. The wreckage would have briefly ringed Venus before falling into the atmosphere, where researchers say it would have been destroyed.

The story doesn't close there. Some research holds that early Venus resembled Earth and may have had oceans, until a runaway greenhouse effect made it uninhabitable. Study leader Stephen Kane of UC Riverside said the loss of a moon could be tied to that shift. The moon Venus swallowed might be part of how it became a hellscape.

Nothing of the moon is left to examine. The one place to look is underground, in how seismic waves travel through Venus.

Read the full story at EarthSky, September 15, 2026

Hot Take: Earth's moon is still drifting outward. Some planets just don't know how to let things go.