Giant Impacts and the Origin of Atmospheres & Oceans
How did Earth and other terrestrial planets acquire their present-day volatile element budgets?
To date, nearly 6,000 planets beyond our solar system (known as exoplanets) have been discovered, revealing a huge diversity in mass, composition, and size. This diversity is largely driven by their inventories and distributions of volatile elements (e.g., C, N, H, noble gases) – major components of atmospheres and oceans that play a fundamental role in planetary evolution and habitability. How planets acquired and retained their volatile elements, however, remains a fundamental, unanswered question. It is thought that most of a planet’s volatiles are acquired during the main stages of planetary growth. Therefore, the atmospheres and oceans of the smaller bodies from which Earth and other planets grew must have partially survived the violent conclusion of accretion, the giant impact phase, for those planets to have retained atmospheres and oceans until today. Giant impacts — planet–planet collisions such as the event that formed Earth’s Moon — play a crucial role in the chemical evolution of planets. Critically, they can remove significant amounts of a planet’s atmosphere and/or ocean. Quantifying the role of giant impacts in shaping a planet’s volatiles is imperative to understanding the origin and evolution of atmospheres and oceans, and ultimately, the processes that make planets habitable.
In the first paper from my PhD, we ran numerical simulations of giant impacts using the smoothed particle hydrodynamics (SPH) code \(\texttt{SWIFT}\) and determined the mechanisms by which a planet’s atmosphere is removed during a collision. This allowed us to develop highly precise equations that quantify how much atmosphere is lost for different types of impact. These can now be incorporated into larger-scale models of planet formation, informing how planetary systems like our own arise. Applying our equations to existing N-body simulations of solar system formation showed that atmospheric loss during giant impacts drastically shapes a planet’s volatile budget, with Earth-like planets losing more than 70% of their atmospheres as a result of multiple giant impacts. We are currently expanding this work to include loss from planets with a wider variety of atmospheres.
Project image credit: Microsoft Copilot AI
