Researchers at the University of California, Riverside, published a study on September 16, 2026, in The Astrophysical Journal suggesting that Venus may have once possessed a moon that was ultimately pulled back into the planet. The celestial body’s exceptionally slow rotation rate naturally caused any satellite to spiral inward and collapse.
Why Venus Has No Moon: A Slow-Rotation Mystery
Venus is similar to Earth in size, mass, and structure, leading astronomers to long view it as our planet’s twin. Yet it stands out in the inner solar system by lacking a natural satellite. For years, scientists debated two primary hypotheses to explain the missing moon: either Venus never captured a lunar companion during its formation, or any early moon was obliterated in the massive impact from another celestial object.
A study published in The Astrophysical Journal offers a different mechanism. According to the research, Venus did not require a dramatic external event to lose its companion. Instead, the planet’s own gravitational pull acting against its sluggish spin sealed the satellite’s fate.
According to researchers at the University of California, Riverside, this process of celestial cannibalism likely occurred within the first billion years of the solar system’s approximately 4.5-billion-year history, with lead author Stephen Krane (also cited as Stephen Crane) telling Reuters on Monday that if it had a moon, it could not have kept it and that such a moon would have crashed down on the planet in a relatively short time scale.
How Earth’s Spin Pushes Our Moon Away
To understand why a Venusian moon would spiral inward, planetary scientists look to the physics governing our own planet. Earth completes a single axial rotation every 24 hours. That rapid spin generates rotational energy that transfers outward to our moon, pushing it farther away over time.
Researchers track this recession with extreme precision because Apollo 11 astronauts left specialized mirrors on the lunar surface in 1969. Data from these reflectors demonstrate that Earth’s moon is slowly drifting outward at a rate of roughly four centimeters (1.6 inches) per year.
Venus operates under entirely different rotational rules. The planet takes 243 Earth days to complete just one rotation on its axis—moving more than 200 times slower than Earth and taking slightly longer to rotate once than it does to complete an orbit around the sun. When computer models simulated planetary physics for a slow-rotating world, the gravitational dynamics produced the reverse outcome: instead of retreating, any hypothetical moon would lose angular momentum and drift steadily inward.
Simulating the Gravitational Collapse of Hypothetical Moons
To test the theory, the research team developed computer simulations to track how planets and moons interact gravitationally. The model was initially tested on the Earth-Moon system to confirm it accurately reproduced real-world mechanics. When applied to Venus, the simulation tested hypothetical moons with masses ranging from half the mass of Earth’s moon up to ten times its mass.
The results surprised the research team because computer models accounted for planetary physics and the gravitational interaction of hypothetical satellites across varied parameters with consistent results. As reported by outlets including Cyprus Mail covering the study in The Astrophysical Journal, in all scenarios considered, the satellites would sooner or later have fallen onto the planet.
While the models demonstrate that any ancient moon could not have survived indefinitely under Venusian physics, scientists emphasize that this does not serve as direct proof a moon actually existed. No physical evidence has been recovered to confirm an ancient lunar companion.
Searching for Hidden Clues Beneath a Toxic Surface
Finding direct proof of an ancient lunar collision remains difficult due to Venus’s active geological history. Roughly 80% of the planet’s surface shares a similar age, pointing to a large resurfacing event that occurred approximately a billion years ago and likely erased older surface records.
Researchers suggest that clues to an ancient impact might instead reside deep within the interior. On Earth, seismic studies have identified unusual structures far below the surface that scientists link to the massive collision believed to have formed our own moon. Similar internal measurements of Venus could eventually reveal whether the planet absorbed a satellite.
Such a collision would have dramatically altered the planet’s rotation, geology, and climate by dumping enormous amounts of energy and angular momentum into Venus. That dramatic shift could hold answers about whether the planet once featured environments more favorable to life before a runaway greenhouse effect scorched surface temperatures up to 880 degrees Fahrenheit (471 degrees Celsius), hot enough to melt lead.
Scientists hope upcoming observational data will clarify the planet’s history. NASA plans to launch two missions in the late 2020s or early 2030s, dubbed DAVINCI+ and VERITAS, to study the atmosphere and geological features of Earth’s nearest planetary neighbor.