Interpreting Dune Patterns: Insights from Earth and Mars

A recent study published in the journal Geology attempts to interpret the patterns of dunes, which are sand mounds frequently formed by aeolian (wind) processes and range in size from small ripples observed on beaches to massive structures observed in the desert. Specifically, the researchers focused on patterns of dune crestlines, which are the top of the dunes. Different dune crestline patterns might appear as mundane features, but their formations are often the result of a myriad of influences, including climate change, surface processes, and atmospheric phenomena.

However, questions pertaining to the processes responsible for the different crestline patterns have baffled scientists. But the findings from this recent study could provide researchers insights into environmental variances not only on Earth, but other dune-harboring planetary worlds in our own solar system. These currently include three of the four terrestrial planets, Venus, Earth, and Mars; smaller bodies such as Jupiter’s volcanic moon, Io; Saturn’s largest moon, Titan; and even dwarf planet Pluto.

“When you look at other planets, all you have is pictures taken from hundreds to thousands of kilometers away from the surface,” said Dr. Mathieu Lapôtre, who is an assistant professor of Earth and planetary sciences in the Stanford Doerr School of Sustainability, and a co-author on the study. “You can see dunes – but that’s it. You don’t have access to the surface. These findings offer a really exciting new tool to decipher the environmental history of these other planets where we have no data.”

Dune interactions are defined as when their crestlines are near one another, and it’s these interactions result in the dunes establishing a balance, or equilibrium, with their surrounding environment. Therefore, the researchers hypothesized that a large amount of dune interactions could be interpreted as recent or nearby changes regarding those confined conditions.

For the study, the researchers analyzed changes in specific known environmental conditions, including sand quantity and wind direction, using orbital images of dune field sites numbering 30 and 16 on Earth and Mars, respectively. Examples of Earth dune field sites included Rice Valley, White Sands, the Namib Desert, and the Tengger Desert. Examples of Martian dune field sites included Nili Patera, Kaiser Crater, Rabe Crater, and Hargraves Crater.

For Earth, the researchers flattened a dune field in China’s Tengger Desert to establish a baseline prior to analyzing satellite imagery between 2016 and 2022 of how this flat terrain evolved into large dunes as they slowly reached a state of equilibrium with their surrounding environment. This was followed by the team examining how wind conditions in the Namib Desert resulted in increased dune interaction as the dunes migrated throughout a valley whose landscape transitions from unrestricted to restricted then unrestricted afterwards.  

“As both sand and winds get funneled into the valley, the dunes feel a change in their boundary conditions, and their pattern needs to adjust,” said Colin Marvin, who is a PhD student in the Department of Earth and Planetary Sciences at Stanford, and lead author of the study. “They move into the portion outside the valley, and they again readjust to their unconfined conditions, and we see a drop in the number of interactions. This trend is exactly what we expected to see.”

For Mars, the researchers used orbital imagery to discover similar dune patterns, specifically near the Martian north pole where the researchers observed minor amounts of dune interactions. This was due to the dunes reaching a state of equilibrium with their surrounding environment, resulting in relative spacing from each other and similar characteristics for both appearance and size. However, dunes observed in slightly lower latitudes exhibited greater amounts of interactions due to changing winds and local surface frost. But once these dunes migrate closer to the north pole, their patterns settle out resulting in decreased interactions.

“We have an upper bound on the time that it takes for a given dune to adjust to changes in environmental conditions, and that is the time it takes for a dune to migrate by a distance of one dune length,” said Marvin. “We can use this to diagnose recent changes in environmental conditions on planetary bodies where we don’t have any information other than images taken from orbit or radar for example.” 

Dr. Lapôtre noted that gaining insights about dune patterns on Mars could not only help better understand Mars’ recent climate, but also assist in locating subsurface water ice that could be excavated by future astronauts on the Red Planet.

As stated earlier, other planetary bodies besides Earth and Mars possess dunes that could be used to better understand climates on those worlds, with one such world being Saturn’s largest moon, Titan. In addition to its dunes, Titan is the only moon that possesses a thick atmosphere, which makes it a target for astrobiology and the search for life beyond Earth. This large moon was extensively investigated by NASA’s Cassini throughout the 2000s and 2010s with the European Space Agency’s Huygens probe touching down on Titan’s surface in January 2005. This made Huygens the first spacecraft to land on a planetary body in the outer solar system and the first landing on a moon aside from Earth’s Moon. While Huygens only transmitted data and images back to Earth for approximately 90 minutes, it provided scientists with a first-time, up-close look at one of the most intriguing moons in the solar system.

This most recent study has helped scientists lay the foundation for helping us better understand dune interactions on other worlds, but NASA’s upcoming Dragonfly mission to Titan hopes to confirm these findings when it lands on the moon’s surface sometime in the 2030s. With this mission, Dragonfly will become only the second rotorcraft sent to another world—the first being NASA’s Ingenuity helicopter on Mars—and will mark the first powered flight on any moon. During its multi-year science mission, Dragonfly will perform short flights around Titan in hopes of determining its prebiotic chemistry and potential for extraterrestrial life but should also provide scientists an up-close investigation of its dunes, which have thus far only been observed from orbit.

What new discoveries about dune interactions on Earth and other worlds will scientists make in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!