Single Large Impacts and their Consequences on the Evolution of a Coupled Atmosphere-Interior Venus Model

Abstract:

We investigate the effect of a single large impact during the Late Veneer and Late Heavy Bombardment on the evolution of the mantle and atmosphere of Venus. We use a coupled interior/exterior numerical code based on StagYY and developed in Gillmann and Tackley [2014]. Single vertical impacts are simulated as instantaneous events affecting both the atmosphere and mantle of the planet by (i) eroding the atmosphere, causing atmospheric escape, and (ii) depositing energy in the crust and mantle of the planet. Main impactor parameters include timing, size/mass, velocity and efficiency of energy deposition.

We observe that volatile delivery by the impactor and impact erosion of the atmosphere are both minor effects compared to melting and degassing triggered by the energy deposited in the mantle and crust.

Small collisions (under 100 km radius) have only local and time-limited effects. Medium-sized impactors (100-300 km) will not have much more consequences unless the energy deposition is enhanced, for example by a fast collision. In that case, it will have comparable effects to the larger category of impacts (400-800 km): a strong thermal anomaly affecting both crust and mantle and triggering melting and a change in mantle dynamics patterns.

Such an impact is a global event and can be responsible for volcanic events focused at the impact location and near the antipode. Depending on the timing of the impact, it can also have major consequences on the long-term evolution of the planet and its surface conditions by either (i) efficiently depleting the upper mantle of the planet, leading to the early loss of its water or (ii) imposing a volatile rich and hot atmosphere for billions of years. Due to the coupled nature of the evolution, both cases can affect the evolution of the whole planet (atmosphere and interior) on the long term.