Persistent or repeated surface habitability on Mars during the late Hesperian - Amazonian

Abstract

Large alluvial fan deposits on Mars record relatively recent habitable surface conditions (≲3.5 Ga, Late Hesperian - Amazonian). We find net sedimentation rate 20 Myr on the total time interval spanned by alluvial fan aggradation, >103-fold longer than previous lower limits. A more realistic approach that corrects for craters fully entombed in the fan deposits raises the lower bound to >(100–300) Myr. Several factors not included in our calculations would further increase the lower bound. The lower bound rules out fan formation by a brief climate anomaly. Therefore, during the Late Hesperian - Amazonian on Mars, persistent or repeated processes permitted habitable surface conditions.