Planetary Geoscience

We describe the flow of liquids – water in the inner Solar System, hydrocarbons on Saturn’s moon Titan – and its effects on planetary surfaces. Liquids fall onto, flow through, and emerge from planetary landscapes. The resultant entrainment, transport, and deposition of sediment are observed in a variety of forms, which can be ascribed to the variety of surficial and subsurface flow conditions. As the area within the highest topographic elevations surrounding a river network, the drainage basin provides a natural hydrologic unit for defining and discussing these various processes. In cratered landscapes on Mars and Titan, drainage divides are often obscured by impact craters and by atmospheric degradation, although in younger terrains the crater rims themselves often demarcate the drainage divides. River networks exhibit morphologies based on surface and subsurface controls on the flow. Whereas networks on Earth are primarily dendritic (branching in a tree-like fashion), the majority of network morphologies on Titan are rectangular, suggesting tectonic influence. Deposits from channelized flow provide data on the flow conditions and sediment load. Fans on Mars and Titan provide evidence of subaerial deposition. Deltaic deposits on those bodies, along with possible shorelines and inferred tsunami deposits around the northern lowlands of Mars, imply deposition and erosion in lakes, seas, and perhaps even a vast martian ocean. Fluvial, alluvial, and lacustrine landforms thereby provide insights into climate, surface, and sedimentologic processes on planetary bodies.