Title: The role of surface water in the geometry of Mars' valley networks and its climatic implications,
Abstract: Mars' surface bears the imprint of valley networks formed billions of years
ago and their relicts can still be observed today. However, whether these
networks were formed by groundwater sapping, ice melt, or fluvial runoff has
been continuously debated. These different scenarios have profoundly different
implications for Mars' climatic history, and thus for its habitability in the
distant past. Recent studies on Earth revealed that channel networks in arid
landscapes with more surface runoff branch at narrower angles, while in humid
environments with more groundwater flow, branching angles are much wider. We
find that valley networks on Mars generally tend to branch at narrow angles
similar to those found in arid landscapes on Earth. This result supports the
inference that Mars once had an active hydrologic cycle and that Mars' valley
networks were formed primarily by overland flow erosion with groundwater
seepage playing only a minor role.