Giant impacts on Venus: lasting consequences on interior dynamics and volcanism, or the lack thereof.

Giant impacts were common in the early evolution of the Solar System. Such an impact has been suggested to have affected the rotation of Venus and possibly its thermal evolution, causing long-lived volcanic activity.

Here, we explore a range of possible giant impacts using smoothed particle hydrodynamics (SPH). We analyse the post-impact rotation and debris disc masses to identify scenarios that can reproduce Venus’ present-day characteristics. We model post-impact interior dynamics evolution using the StagYY convection code, by transferring the thermal field obtained through SPH simulations into a 2D spherical annulus geometry. We account for the low viscosity of molten volumes of the mantle above 35% melt fraction by using an effective "eddy" thermal conductivity of 10¹⁰ W/(m.K) following Lourenço et al. (2020), and the heat flux is parametrized following Abe (1993, 1997). The evolution of the core uses a 1D parameterized model to track the temperature profile and the growth of the inner core.

We observe that a wide range of impact scenarios are consistent with Venus’ current rotation for both head-on collisions on a non-rotating Venus and oblique, hit-and-run impacts on a rotating Venus. Collisions that match consistent rotation rates typically produce minimal debris discs residing within Venus’ synchronous orbit (Bussmann et al., 2025). We select these favourable scenarios to model their long-term interior evolution.

In the simulations, giant impacts expectedly produce surface magma oceans. Their relative depths vary between different simulations depending on impact properties: from a shallow melt layer in the order of 100 km thick to a fully molten mantle from surface to core-mantle boundary for the most energetic impacts (high impactor mass and velocity). If the surface is able to radiate heat to space efficiently, the magma ocean cools down quickly and first reaches the rheological transition (35% melt fraction) in a few 100-1000 yrs. Full solidification (0% melt fraction) can take longer because of the effects of the impact on the deep interior.

Indeed, as highlighted by Marchi et al. (2023), giant impacts also deposit a considerable amount of energy in the upper layers of the core, which translates into temperatures reaching up to 10⁴ K. This causes the base of the mantle to fully melt. The resulting liquid layers (in the core and the mantle) convect vigorously and cool the core rapidly (~10⁴ years). The very hot mantle melt is buoyant and rises toward the surface through the solid mantle on timescales of 10⁴-10⁵ yrs. Plumes formed in such a way persist until the excess of heat is extracted from the core and the lower mantle reaches the rheological transition. Solidification of the surface can be delayed by plumes, but models indicate that a fully solid state is reached in a few 1-10 Myr.

After a few hundred million years, the thermal evolution of a Venus-like planet that experienced a giant impact becomes similar to that of cases devoid of impacts. The characteristics of the convection regime in both cases do not substantially differ at present-day (after 4.5 Gyr).