Early Mars climate near the Noachian-Hesperian boundary: Independent evidence for cold conditions from basal melting of the south polar ice sheet (Dorsa Argentea Formation) and implications for valley network formation

► South polar eskers indicate wet-based glaciation near Noachian-Hesperian boundary. ► Glacial accumulation/ice-flow models distinguish bottom-up and top-down heat sources. ► For basal melting at typical heat flux, mean annual T must be raised from −50 to −75 °C. ► This range implies equatorial seasonal temperatures in excess of water melting point. ► Provides independent estimate of Noachian-Hesperian boundary elevated temperatures.