Mars has weird dunes due to its low atmospheric stress and unusual winds
In a recent study published in Nature Communications, an international team of researchers led by Stanford University used artificial intelligence (AI) to study the formation of sand waves and sand dunes of two different sizes on Mars. These formations could help scientists better understand the atmospheric history of Mars by using statistical analysis to study the fossilized forms of these aeolian (windblown) structures.
Wind-blown sand is common on both Earth and Mars, with the notable difference being that Mars has a far lower atmospheric pressure than Earth, on the order of 6.518 millibars (0.095 psi) compared to the 1013.5 millibars (14.7 psi) of Earth, which is 0.6% of Earth’s atmospheric pressure. Two commonly observed formations of windblown sand are small ridges known as “impact waves” that result from sand grains impacting sand mounds, and the second form is much larger sand dunes that can stretch for several kilometers (miles).
The reason why the atmospheric history of Mars could be further explored from this study may lie in an exact and consistent mathematical relationship between the lack of atmospheric pressure on Mars and the size of the windblown sand dunes and sand waves on the red planet, they have been observed to occur at all but the smallest dimensions.
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“This is particularly important because Mars is believed to have had a thicker atmosphere in the past, which may have sustained Earth-like surface conditions,” Dr. Mathieu Lapôtre, an assistant professor of geological sciences at Stanford Doerr School of Sustainability and a co-author of the study, said in a statement. “However, it lost most of it and we don’t really know when, how quickly and why.”
This study came after scientists were puzzled by images from NASA’s Curiosity Mars rover in 2015, which observed similar wind-blown patterns on the surface of Mars. These include huge sand dunes along with smaller formations like the impact waves seen on Earth, but also formations that are about 10 times the size of these waves but smaller compared to sand dunes. Essentially, Curiosity observed a type of medium-sized sand formation that had never been seen before.
NASA’s Curiosity Mars rover stitched together a “selfie” from 53 combined images taken on January 19, 2016 by Namib Dune. (Source: NASA/JPL-Caltech/Malin Space Science Systems)
A proposed hypothesis for these medium-sized sand formations may come from the continued growth of impact waves due to low atmospheric pressure on Mars. dr Lapôtre and other scientists have previously suggested that these formations may result from something called hydrodynamic (fluid motion) instability, which can be used for both fluid and air motion.
For the study, researchers used AI and more than 130,000 high-resolution images of Mars to perform quantitative analysis on one million barchan dunes, also known as crescent-shaped dunes, on Mars to study how their size and shape differ on the Martian surface varies. Barchan dunes are common on both Earth and Mars and have been imaged extensively on the Red Planet by the HiRISE camera on board NASA’s Mars Reconnaissance Orbiter.
A color-enhanced image of Barchan Dunes west of Mawrth Vallis on Mars taken on December 30, 2013 by the HiRISE camera aboard the Mars Reconnaissance Orbiter. (Image credit: NASA/JPL-Caltech/University of Arizona)
Their results suggest that these medium-sized sand formations are not impact waves, but are like miniature sand dunes that stop growing at a certain point due to the predicted change in fluid-like airflow in the low atmospheric pressure near the Martian surface.
“Impact waves form on Mars in exactly the same way as on Earth and are more or less the same size,” says Dr. Lior Rubanenko, the lead author of the study, while conducting the research as a postdoctoral fellow in geology at Stanford. said in a statement. “That makes sense because the mechanism that forms impact waves has less to do with the properties of the atmosphere and more to do with the mechanics of sand transport.”
“Now that we know how the size of these waves varies with atmospheric density and why, we can use the size of fossilized waves in very old rocks to reconstruct the history of the Martian atmosphere,” said Dr. Lapotre.
As always, keep doing science and keep looking up!