Venus May Have Lost a Moon to Its Own Changing Spin

Venus may not have always been moonless. A new study based on computer simulations suggests the planet could have formed with a satellite that was eventually pulled back into Venus by changes in the planet’s rotation. The research, led by Stephen R. Kane and posted as a preprint on arXiv, examined how a hypothetical moon might have evolved over 4.5 billion years. The model incorporated Venus’s spin, the imagined moon’s mass and orbital distance, and the effects of internal tidal friction. The simulations produced different outcomes depending on those starting conditions. In some cases, a moon remained in orbit for the entire modeled history of the solar system. In others, it was destroyed. Many of the scenarios leading to destruction followed a complicated path: the moon initially moved farther from Venus, but later began traveling inward as Venus’s spin changed. The researchers’ favored explanation is that the moon eventually spiraled back toward the planet. Their calculations indicate that this could have occurred between 30 million years and 1.7 billion years after the moon formed, depending on its mass and Venus’s original rotation rate. The study does not establish that Venus definitely once had a moon. Instead, it presents possible histories for a satellite that is no longer present and identifies the conditions under which it would have survived or disappeared. According to the researchers’ interpretation, no outside collision would have been required to remove the moon. Its fate may have followed naturally from the early characteristics of the Venusian system. The authors suggest that whether Venus retained a moon during its early history could have influenced how the planet diverged from Earth, which is similar to Venus in size and density but has a moon of its own. Because the work is based on a preprint and simulations of hypothetical conditions, the question remains open. The study offers a possible explanation for Venus’s missing satellite, rather than a definitive reconstruction of what happened.