New scientific research suggests that Venus, Earth’s neighbouring planet, may have ‘swallowed’ its own moon around 4.5 billion years ago. This surprising theory proposes that if Venus once had a moon, its unique slow rotation would have caused it to spiral inward and eventually collide with the planet.
The study, conducted by scientists at the University of California, Riverside, aims to explain why Venus, despite being similar in size to Earth, currently lacks a natural satellite. Lead author Stephen Kane, an astrophysicist at UCR, stated, “If [Venus] had a moon, and it likely did at some point, it could not have kept it.”
Venus’s Slow Spin: The Key Factor
Unlike Earth’s moon, which is gradually moving away from our planet by about four centimetres per year due to Earth’s relatively fast 24-hour rotation, Venus presents an opposite scenario. The second planet from the Sun takes an extraordinary 243 Earth days to complete a single rotation – longer than its 225-day orbit around the Sun. According to Kane, this extremely slow spin, combined with the planet’s gravity, would cause any orbiting moon to lose altitude and spiral inwards towards a collision.
To test this hypothesis, the UCR team developed computer models based on the gravitational interactions of planetary bodies. After successfully replicating the known evolution of Earth and its moon, they simulated various scenarios for Venus, altering its rotation rate and the size of hypothetical moons. In most simulations, regardless of the moon’s mass, the outcome was the same: the moon crashed into Venus. Kane expressed surprise at the consistency of the results, noting, “It all went pretty much in the same direction.”
Implications and Future Research
This research offers a compelling explanation for Venus’s lack of a moon and challenges previous theories that suggested Venus either never formed a moon or that a moon was destroyed by a catastrophic collision with another space object. The UCR study, published in The Astrophysical Journal, indicates that a catastrophic event wasn’t necessary for Venus to be moonless today. However, it’s important to remember that the findings do not definitively prove Venus ever had a moon, only that if it did, it would not have survived.
Such a collision could have had significant consequences for Venus, potentially altering its rotation, geological features, and climate. This raises questions about whether Venus, often referred to as ‘Earth’s twin’ due to their similar sizes, was ever capable of hosting life. Evidence of such an impact would be challenging to find on Venus’s surface, as approximately 80% of it is of a similar age, suggesting a major resurfacing event roughly a billion years ago. Scientists hope that future Nasa missions, DAVINCI+ and VERITAS, will provide more insights by studying the planet’s atmosphere and geological features.
The implications also extend to the search for habitable worlds beyond our solar system. Scientists often consider the presence of a large moon as a factor influencing a planet’s habitability, as Earth’s moon drives tides and may contribute to geological activity. Kane’s findings suggest that even planets capable of forming moons might not be able to retain them if they rotate slowly, impacting their evolution. “My study shows a disturbing scenario for many of those cases,” Kane commented in an interview cited by Phys.org, referring to slow-rotating exoplanets.
