Planetary scientists may have finally cracked the mystery of Venus's bizarre rotation. A new paper, presented at the recent European Geosciences Union General Assembly in Vienna, proposes that a high-velocity, moon-sized impactor struck the planet early in its history. This collision would have set the planet spinning slowly backward on its axis.
The finding tackles a long-standing puzzle in planetary science. Venus rotates in a retrograde direction, meaning it spins opposite to most planets in our solar system, and does so at an agonizingly slow pace—one full rotation takes 248 Earth days. The new models offer a plausible origin story for this odd behavior.
According to the research, the impact likely occurred within the first 50 million years after Venus formed. The authors argue that a high-angle strike from a moon-sized object would have been energetic enough to reverse and slow the planet's rotation. The models presented at the conference support this scenario.
If confirmed, this would establish a dramatic early event as the root cause of one of Venus's most puzzling features. It also underscores how profoundly giant impacts can shape planetary evolution, influencing everything from axial tilt to the length of a day.
Future observations or sample-return missions could potentially test this impact hypothesis by analyzing Venus's crust and mantle composition for signatures of such a cataclysmic event.