Impact induced H2-rich climates on early Mars explored with a global climate model

Abstract

The impact heating hypothesis has been explored as a means of warming early Mars and inducing rainfall through the potential injection of water, energy, and reducing greenhouse gases to the atmosphere. We simulate H2-rich post-impact scenarios with the 3D NASA Ames legacy early Mars Global Climate Model (eMGCM) for 100-km and 250-km diameter impactors to assess the ability of these environments to warm the surface above freezing and induce fluvial erosion. We find that including degassed hydrogen does not extend the short-term period of warm temperatures and heavy rainfall experienced immediately after an impact, but does provide enough warming in the final climate state to raise mean annual surface temperatures ≥273 K. These warm conditions would be long lived as hydrogen slowly escapes to space (over timescales of 105 years). Predicted precipitation rates in these long lived warm conditions suggest that a handful of large impacts (100 km in diameter or greater) could be capable of inducing a significant amount of the total Noachian erosion (~1–10 m per 100-km impact event and ~10–100 m per 250-km impact event). Simulations of a Hellas-sized impact event with H2 degassing are very sensitive to surface water reservoir assumptions. Scenarios range from wet conditions with widespread precipitation to conditions where water is trapped at the poles / over Tharsis. Overall, more work is needed to understand hydrological cycle sensitivities in H2-rich climates, but we confirm the ability of impacts to induce transient warm and wet conditions on early Mars is much better than previously thought if those impacts degassed H2 in thick CO2 atmospheres.