Reconstructing river flows remotely on Earth, Titan, and Mars.

Current understanding of alluvial rivers is limited by the lack of field data on Earth, low-resolution spacecraft data on Titan, and the inactivity of ancient Martian rivers. These limitations make it difficult to reconstruct past surface conditions and hydrological activity on these bodies. While Earth's rivers are known to carry fluid and sediment that reflect upstream climate and erosion, many remain unsurveyed. On Mars, inactive river channels provide clues about past environments, but their interpretation is hindered by the absence of active flow. Titan's rivers, observed only indirectly, remain poorly understood in terms of their sediment transport and flow characteristics. This gap motivates the need for a method that uses only remote sensing data to infer river behavior across planets. Existing techniques rely on in situ measurements, which are not always feasible. This uncertainty drives the development of dimensionless scaling laws that can predict flow and sediment transport using only channel width and slope. Prior research has shown that these laws can describe Earth's rivers, but their application to extraterrestrial settings is novel. No prior work had resolved how these scaling laws might apply to rivers on Titan or Mars. This paper addresses that gap by testing the method on all three planetary bodies.

The goal of this research is to develop a method for reconstructing river flow and sediment transport conditions using only remote sensing data. The study focuses on alluvial rivers on Earth, Titan, and Mars, where field measurements are either unavailable or impractical. The motivation is to overcome the limitations of current data sources and provide a consistent framework for interpreting river behavior across planetary environments. By using dimensionless hydraulic geometry relations, the researchers aim to predict in-channel conditions without requiring direct measurements. This approach is particularly valuable for planets where in situ data are sparse or nonexistent. The study also seeks to test whether these scaling laws can be applied across different planetary bodies with varying gravity and fluid properties. The researchers propose that the method can help interpret spacecraft observations of Martian and Titanian rivers. Additionally, the study aims to provide a template for future planetary surface reconstructions using remote sensing data.

The researchers applied dimensionless hydraulic geometry relations to predict river flow and sediment transport conditions. These relations are scaling laws that link channel dimensions to flow and sediment transport rates. The method uses only remote sensing measurements of channel width and slope, which are more readily available than in situ data. The approach was tested on rivers on Earth, Mars, and Titan to assess its applicability across planetary environments. For Earth, the method was validated against rivers with known flow and sediment characteristics. On Mars, the researchers compared predicted grain sizes with those measured by the Curiosity and Perseverance rovers. For Titan, the method was used to estimate sediment fluxes to the coast of Ontario Lacus. The study also examined whether the distinct dynamics of bedload-dominated, suspended load-dominated, and bedrock rivers produce distinct channel characteristics. The researchers used spacecraft data to extract channel width and slope for Martian and Titanian rivers. The method does not require assumptions about fluid properties or sediment composition, making it broadly applicable.

The method successfully predicted flow and sediment flux in Earth rivers that lack field measurements. The results showed that bedload-dominated, suspended load-dominated, and bedrock rivers have distinct channel characteristics. On Mars, the predicted grain sizes at Gale and Jezero craters overlapped with rover measurements. The method also reconstructed past flow conditions consistent with long-lived hydrologic activity at both craters. For Titan, the predicted sediment fluxes suggest that the river delta at Ontario Lacus could form in as little as 1,000 years. The scaling relationships indicate that Titan's rivers may be wider, have gentler slopes, and transport sediment at lower flows than Earth or Mars rivers. The method's predictions align with spacecraft observations of Martian and Titanian rivers. The results support the use of dimensionless scaling laws for remote reconstruction of river properties across planetary bodies.

The study concludes that dimensionless hydraulic geometry relations can predict river flow and sediment transport conditions using only remote sensing data. The method is effective for Earth rivers that lack field measurements and for reconstructing past conditions on Mars and Titan. The distinct dynamics of different river types produce distinct channel characteristics, which the method can identify. The predicted grain sizes on Mars match rover measurements, supporting the method's accuracy. The results suggest that Titan's rivers may transport sediment at lower flows than Earth or Mars rivers. The method provides a template for interpreting spacecraft observations of alluvial rivers on other planets. The researchers propose that this approach can be used to reconstruct surface conditions on planetary bodies where in situ data are limited. The findings support the use of remote sensing for planetary hydrology and geomorphology.