Impact heating of the early Martian climate
Kathryn Steakley, NMSU Astronomy
The nature of Mars’ ancient climate has been the subject of debate for decades. Abundant geologic evidence suggests that liquid water flowed on the surface of Mars during the late Noachian and early Hesperian eras (~3.5 – 3.8 billion years ago), but climate models struggle to reproduce such warm and wet conditions. Characterizing the climate that supported this aqueous activity and constraining the duration and intensity of warm and wet periods is crucial to understanding whether Mars was habitable in the past. 1-D climate modeling studies suggest that asteroid impacts are capable of inducing greenhouse warming on early Mars due to the substantial amounts of energy and water that are injected into the atmosphere (Segura et al., 2008). We use a 3-D global climate model (GCM) to simulate the post-impact climate conditions presented in Segura et al. (2008) (30-, 50-, and 100-km impactors in 150 mbar, 1 bar, and 2 bar atmospheres) and examine the resulting global distributions of surface temperatures and precipitation to assess whether these post-impact climates can facilitate valley network formation in Mars’ southern highlands. We find that these post-impact scenarios do result in above-freezing temperatures and 10s of cm of rainfall in the southern highlands, but that ultimately these warm and wet periods are short lived (on the order of years) and do not support the sustained warm and wet conditions that facilitate valley network formation. We find that scenarios with high surface pressures and scenarios with radiatively active clouds experience longer periods of above-freezing temperatures and result in higher final mean annual temperatures (up to 272.8K in our warmest scenario). In future work, we will investigate other greenhouse gases delivered by impacts in addition to water, including hydrogen and/or methane, to test whether this prolongs the warm and wet periods following impacts.