Early Mars Climate History: Characterizing a “Warm and Wet” Martian Climate With a 3‐D Global Climate Model and Testing Geological Predictions

Abstract

AbstractObservations of Late Noachian‐Early Hesperian‐aged Martian surfaces reveal valley networks, lakes, degraded craters, and putative oceanic shorelines, often interpreted to require a persistent “warm and wet” climate, characterized by mean annual temperature >273 K and abundant rainfall. We simulate this “warm and wet” climate (global mean annual temperature ~ 275 K) with a 3‐D global climate model to determine whether these features could have formed in this climate through rainfall activity. We find that rainfall is limited in abundance and areal distribution, precipitation is dominated by snowfall, and highlands temperatures are <273 K for the majority of the year. We conclude that, in this simulated climate scenario, (1) Late Noachian‐Early Hesperian valley networks and lakes could not have formed through rainfall‐related erosion, (2) crater degradation by rainsplash and runoff is not predicted, (3) global clay formation through long‐lived rainfall, fluvial activity, and warm temperatures is unlikely, and (4) the presence of a rainfall‐ and overland flow‐fed northern ocean is improbable.