Venus may have swallowed its own moon early in the planet’s history, according to an astrophysics study published on September 14 in The Astrophysical Journal. Researchers from the University of California, Riverside, suggest that the extremely slow axial rotation of Earth’s planetary neighbor doomed any natural satellite to spiral inward and crash into the surface.
Planetary Rotation and Lunar Decay
Venus takes 243 Earth days to complete a single rotation on its axis, moving significantly slower than Earth’s 24-hour cycle. According to lead study author and astrophysicist Stephen Krane, this sluggish spin rate prevents tidal forces from pushing a moon outward. Instead, gravitational mechanics cause any orbiting satellite to lose energy, spiral closer to the planet, and ultimately disintegrate in a cataclysmic impact.
Computer simulations based on planetary physics demonstrated that hypothetical Venusian moons of various sizes would all meet the same destructive fate. Krane told Reuters that if Venus possessed a moon in its infancy, the satellite could not have maintained its orbit and would have crashed down rapidly.
Comparing Earth and Venusian Dynamics
The research highlights a stark contrast between Earth and Venus regarding lunar survival. Earth rotates more than 200 times faster than Venus, a velocity that transfers energy to our moon and pushes it outward at a rate of 4 centimeters (1.6 inches) per year, as measured by Apollo 11 retroreflectors left on the lunar surface in 1969.
By contrast, Venus lacks this rotational momentum. Scientists previously theorized that Venus either never acquired a moon or lost one to a massive impact with an external celestial object. The new UC Riverside model indicates that a moon-gobbling event likely unfolded within the first billion years of Venusian history, which spans roughly 4.5 billion years like the rest of the solar system.
Future Exploration of Venus
Despite the lack of physical proof for an ancient Venusian moon, scientists note that the early inner solar system was crowded with rocky objects. Venus likely absorbed frequent impacts due to its close proximity to the sun. Researchers hope forthcoming NASA missions, including DAVINCI+ and VERITAS scheduled for launch in the late 2020s or early 2030s, will provide deeper data on the atmospheric and geologic history of the planet.
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