New Simulation Suggests Venus May Have Devoured Its Own Moon

Astronomers may have resolved a long-standing mystery regarding why Venus, often called Earth’s sibling, lacks a moon. According to new research, the solar system’s hottest planet may have consumed its own natural satellite billions of years ago. While Earth boasts a large lunar companion, Venus and Mercury remain the only planets in our solar system without moons.

Stephen R. Kane, a researcher at the University of California, Riverside, and lead author of the study, noted that Venus shares Earth’s size, mass, and rocky composition. Consequently, scientists have debated whether the planet never formed a moon or if it subsequently lost one. “Venus undoubtedly experienced large impacts, just as Earth has, and so has had as much, if not more, opportunity to form a moon similar to what we see in our own skies,” Kane explained.

To test these hypotheses, Kane and his colleagues developed a simulation based on fundamental physics, validating their model by successfully reproducing the known evolution of the Earth-moon system. The team modeled the gravitational dynamics between Venus, a hypothetical moon, and the sun over billions of years. They utilized two independent mathematical descriptions of tidal forces to ensure their conclusions were robust across various assumptions about Venus’s initial spin rate and the moon’s mass.

The findings indicate that, unlike Earth’s moon which is gradually drifting away, a moon orbiting Venus would typically reverse its trajectory and spiral inward. The modeling suggests that such a moon would eventually be torn apart by Venus’s intense gravity. Counterintuitively, a more massive moon would not fare better; it would actually be destroyed faster because its greater mass would drain Venus’s rotational energy more efficiently, accelerating the inward spiral.

Survival was only possible within a narrow window of conditions: Venus would have needed to be rotating rapidly, with a day shorter than 12 hours, and the moon would need to be no larger than Earth’s. Since current theories suggest early Venus did not rotate this quickly, the likelihood of a surviving moon is low. “Outside that range, the moon is unfortunately doomed to be consumed by Venus,” Kane stated.

Direct evidence of such an event is unlikely to be found, as a destroyed moon would leave minimal trace visible to telescopes today. However, Kane suggests that debris from a consumed moon may have left a chemical fingerprint on Venus’s surface or atmosphere. Upcoming missions, such as NASA’s DAVINCI probe, aim to analyze Venus’s atmospheric composition in detail, potentially uncovering these indirect signs.

The implications of this research extend beyond our solar system. The models predict that slowly rotating, Venus-like exoplanets should generically lack large moons. As astronomers begin detecting moons around distant planets, these predictions can be tested against real data. The research is currently available as a pre-print on the arXiv repository.