Sand dunes reveal atmospheric wind patterns on Mars

Mars is one of the most explored components of the solar system, yet there are always more discoveries to unveil on Earth's planetary neighbor. On Earth we are able to take direct measurements to understand our planet's meteorological activities, but on Mars scientists must use evidence in the landscape to discern this information instead.

One such feature of the red planet's landscape are barchan dunes in deserts, crescent-shaped sand dunes formed by wind patterns predominantly in one direction in areas with a limited supply of sand. Such aeolian-derived dunes are significantly impacted by the atmospheric circulation on the planet's surface, with new research published in Geophysical Research Letters finding that localized topography at scales <100km (such as deep impact craters from rocky or icy meteorites) can deflect winds and cause changes in barchan dune formation.

Dr. Lior Rubanenko, Assistant Professor at the Technion—Israel Institute of Technology, and colleagues used machine learning to characterize Mars' wind patterns based upon the morphology of more than 700,000 barchan dunes. This data was obtained from images taken by a specialized camera on the Mars Reconnaissance Orbiter, a spacecraft that has been orbiting the planet since 2006 to collect information on its geology and climate.

The machine learning component was trained to outline the shape of dunes automatically to map dune fields. From these images the scientists identified the orientation of the steep side (slipface) of the dunes and their tips (called horns) protruding from edges. Where the horns are asymmetrical with one being longer than the other, this indicates the interaction of multiple wind directions.

The research team found a distinct pattern arising in dune migration resulting from summer atmospheric circulation patterns, these being northwards directed at mid-latitudes and cyclonic (counterclockwise movement about a center of low pressure) near the north pole. The latter is also broken into a smaller component experiencing the opposite anticyclonic wind direction, which the authors specifically attribute to the effects of winds moving across the polar ice cap.

At latitudes above 45°N, Dr. Rubanenko and colleagues discovered dune migration patterns are dominantly easterly, matching the cyclonic polar vortex circulation, while at latitudes below this down to -45°N they are southerly-directed. Local wind regimes most keenly affect areas where topographic features are 10–50km in size horizontally, but has little impact when landmarks exceed 100km-scales, these instead being impacted by the larger planetary wind systems.

One limitation of the machine learning project however is that it does not fully consider the complexities of changing wind regimes between day and night and across seasons, but instead focuses on longer-term patterns. It also struggles in areas with significant topographic changes, such as the larger impact craters of Valles Marineris, Hellas and Argyre, where dunes are dispersed across a larger area.

These craters act as sand traps, supplying ample material for the formation of dune fields, which form closer to the center of the crater basin the deeper they are. Migration within craters could be caused by stronger winds blowing down the slopes.

While more refinement of the machine learning technology is required, preliminary research here does track with real data when tested and matches surface evidence for the direction of wind-blown dust and sand during dust storms.

As on Earth, planetary-scale circulation patterns show a general trend moving from the poles to the equator of Mars with disruption in the mid-latitudes. Understanding the atmospheric circulation patterns on Mars is important for supporting manned missions to the planet and the prospect of future habitability.

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