Widespread valley networks (VNs) on Mars and other evidence point to an early warm and wet climate. However, ongoing debates still exist about VN’s formation processes and associated climatic conditions. The power law relationship between basin length and area (Hack’s Law) can be diagnostic of different fluvial processes related to climatic conditions. Past studies of Hack’s Law on Mars at local sites have produced inconclusive results.  Here we used a parameter-free method to delineate watersheds globally on Mars based on mapped VNs and extracted their Hack’s Law exponent (h). The majority of h values on Mars are similar to those in arid areas on Earth, implying similar runoff processes and arid conditions for VN formation on early Mars. Statistical analyses show that the spatial distribution of h on Mars is not random, but with a few clustered high and low values, likely controlled by local conditions (e.g., slope or structures).

While there is a consensus that water played at least some role in the formation of various Martian landforms, including valley networks (VNs), the specific mechanisms and climate conditions are still debated. Basin hypsometric curves, reflecting elevation distributions, offer insights into past processes and climates. Our study presents a global-scale comparison of basin hypsometry on Mars, Earth, the Moon, and artificial fractal surfaces. Results indicate Martian VN formation likely occurred under a climate more arid than hyper-arid Earth, or under more humid periods that were short-lived. Differences in hypsometric attributes between Mars and the Moon suggest VN formation on Mars involved precipitation-driven water flow. Additionally, impact cratering significantly influenced Martian surface conditions, potentially disrupting fluvial erosion processes. This comparative analysis sheds light on the complex interplay of climatic factors and geological processes in Martian landscape evolution.

A document by Wei Luo. Click on the document to view its contents.