The possibility of a giant impact on Venus

Giant impacts were common in the early evolution of the Solar System, and it is possible that Venus also experienced an impact. A giant impact on Venus could have affected its rotation rate and possibly its thermal evolution. In this work, we explore a range of possible impacts using smoothed particle hydrodynamics (SPH). We consider the final major collision, assuming that differentiation already occurred and that Venus consists of an iron core (30% of Venus' mass) and a forsterite mantle (70% of Venus' mass). We use differentiated impactors with masses ranging from 0.01 to 0.1 Earth masses, impact velocities between 10 and 15 km/s, various impact geometries (head-on and oblique), different primordial thermal profiles, and a range of pre-impact rotation rates of Venus. We analyse the post-impact rotation periods and debris disc masses to identify scenarios that can reproduce Venus' present-day characteristics. Our findings show that a wide range of impact scenarios are consistent with Venus' current rotation. These include head-on collisions on a non-rotating Venus and oblique, hit-and-run impacts by Mars-sized bodies on a rotating Venus. Importantly, collisions that match Venus' present-day rotation rate typically produce minimal debris discs residing within Venus' synchronous orbit. This suggests that the material would likely reaccrete onto the planet, preventing the formation of long-lasting satellites - consistent with Venus' lack of a moon. We conclude that a giant impact can be consistent with both Venus' unusual rotation and lack of a moon, potentially setting the stage for its subsequent thermal evolution.