Prolonged Fluvial Activity Revealed by Mapping and Analyses of Valley Networks in the Northwestern Hellas Region, Mars

Abstract

Valley networks (VNs) on Mars are crucial for understanding the Martian hydrologic and climatic history. However, the limited resolution of remote sensing data hindered the complete identification of Martian VNs, affecting our understanding of the formation and duration of VNs as well as their climatic significance. In this study, we utilized high-resolution imaging and topographic data to conduct detailed mapping and investigations of the VNs around the northwestern margin of the Hellas basin, the largest impact basin and major sedimentary sink in the Martian southern highlands. We identified a total of 911 VNs with a cumulative length of 32,086.3 km, more than twice that of previous mapping results. Additionally, we analyzed the morphological parameters of VNs, including stream order, sinuosity, junction angle, stream slope, etc., investigated their geomorphologic characteristics, and determined their formation ages. We propose that occasional precipitation and regional groundwater fostered the formation of well-developed VNs and a “Hellas Ocean” in the Noachian Period. The main fluvial activity occurred during ∼3.9–3.2 Ga. Subsequently, the climate transitioned from warm and semiarid to cold and arid during the Noachian-Hesperian transition, leading to the evaporation of the “Hellas Ocean.” In the Amazonian, some small simple valleys formed during ∼2.1–1.0 Ga with the supply of meltwater associated with obliquity-controlled glacial processes. These results reveal prolonged fluvial activity in the northwestern Hellas region with diverse water sources under changing climatic conditions, which make the region a very promising candidate for future in situ exploration missions.