The role of surface water in the geometry of Mars' valley networks and its climatic implications

TL;DR

This paper investigates the formation of Mars' valley networks, finding evidence that they were primarily shaped by surface runoff, indicating an ancient active hydrologic cycle on Mars.

Contribution

It provides new evidence supporting surface runoff as the main formation process of Martian valley networks, based on their narrow branching angles.

Findings

Valley networks on Mars have narrow branching angles.

Results suggest surface runoff was the dominant formation process.

Mars likely experienced an active hydrologic cycle in the past.

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.