Study Suggests Venus May Have Pulled a Former Moon Into Itself

Venus may once have had a moon that was gradually pulled inward, broken apart and consumed by the planet, according to a recent study led by University of California, Riverside astrophysicist Steven Kane.

Venus is similar to Earth in mass, size and structure, but unlike Earth it has no natural satellite. Earlier explanations proposed that a Venusian moon either never formed or was destroyed in a major collision. The new research offers another possibility based on Venus’ gravity and unusually slow rotation.

Venus takes 243 Earth days to complete one rotation, longer than its year. A planet’s rotation affects whether tidal forces drive a satellite outward or draw it inward. Earth’s faster rotation is causing its moon to recede by about 1.5 inches per year, while the study suggests Venus’ slow spin could have caused a moon to spiral toward the planet.

The researchers tested the mechanism with computer simulations, first checking their model by reproducing the evolution of Earth’s moon. They then varied Venus’ rotation period, the hypothetical moon’s orbit and a lunar mass ranging from 0.01 to 10 times the mass of Earth’s moon. Under many simulated conditions, the satellite moved inward until it fragmented and fell into Venus. In some scenarios involving a much faster Venus rotation and an Earth-moon-sized satellite, a moon survived for as long as 4.5 billion years.

The findings present a possible explanation for Venus’ lack of a moon rather than evidence that such a moon definitely existed.