Published : 16 Sep 2026, 07:02 AM
Updated : 16 Sep 2026, 11:50 AM
A new theory may finally explain why Venus, Earth's closest planetary twin, has no moon -- and the answer, scientists say, is that it probably ate one.
An astrophysicist at the University of California has proposed that Venus's extraordinarily slow rotation would have doomed any natural satellite it once had, causing it to spiral gradually inward before crashing into the planet in a catastrophic collision, reports The Independent.
"If it had a moon, and it likely did at some point, it could not have kept it," said astrophysicist Stephen Krane.
"That moon would have crashed down on the planet in a relatively short time scale."
The study, published Monday in The Astrophysical Journal, used computer models simulating the gravitational mechanics of hypothetical Venusian moons of various sizes.
All met the same fate -- collapsing into Venus, likely within its first billion years.
The key factor, researchers found, was rotational speed. Venus takes 243 Earth days to complete a single rotation -- slightly longer than its own orbit around the Sun, according to he Independent.
Earth, by contrast, spins every 24 hours, more than 200 times faster.
That difference matters enormously. Earth's faster spin transfers energy outward to the Moon, gradually pushing it farther away -- currently at 4 centimetres per year.
Venus, spinning too slowly, would have had the opposite effect, pulling any moon inward to its destruction.
Previous theories held that Venus either never acquired a moon, or lost one to a massive external impact.
The new study marks a departure, pointing instead to the planet's own sluggish spin as the culprit.
Though no direct evidence of a former Venusian moon exists, Krane said it was unlikely Venus escaped the kind of world-shattering early collision believed to have created Earth's moon, given how crowded and violent the early solar system was, states The Independent.
Two forthcoming NASA missions -- DAVINCI+ and VERITAS -- due for launch in the late 2020s or early 2030s, are expected to shed more light on Venus's history.
