Evaluating an impact induced H2-rich climate for early Mars

Abstract:

The impact heating hypothesis has been explored as a means of warming early Mars and inducing rainfall through the potential catastrophic injection of water, energy, and reducing greenhouse gases to the atmosphere. Studies have proposed that impact induced rainfall may have played a role in carving valley networks (VNs), eroding Noachian craters, or forming phyllosilicates. However, multiple studies highlight discrepancies between the impact heating hypothesis and observed geology, including the fact that the largest impacts predate the valley networks, post-impact high rainfall rates could produce a “deluge” effect not conducive to VN formation, and that durations of above-freezing conditions after impacts may simply be too short for significant alteration. Here, we evaluate whether hydrogen degassing in the aftermath of an impact has a significant enough effect on climate to overcome some of these discrepancies. We simulate H₂-rich post impact scenarios with the 3D NASA Ames legacy early Mars Global Climate Model (eMGCM) for multiple CO₂ surface pressures and hydrogen abundances to bracket the range of plausible scenarios that might induce prolonged above-freezing surface temperatures. 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 affect the final climate state. We evaluate precipitation rates and distributions in that final state with respect to geologic observations and assess the difficulties of inducing environments with both consistent precipitation and warm surface temperatures in these climates.