Round sand dunes on Mars puzzle scientists

Sand dunes on Mars: Round dark formations with much smaller ripples of lighter-colored sand between them.
View larger. | NASA’s Mars Reconnaissance Orbiter (MRO) took this photo of round sand dunes on Mars on November 22, 2022. How did they form? Image via NASA/ JPL-Caltech/ University of Arizona.

Sand dunes are common on Mars, and they can be found pretty much everywhere on the planet. So it’s not surprising that we call Mars a desert world. The dunes come in many different shapes and sizes. On March 3, 2023, NASA shared an image from the Mars Reconnaissance Orbiter (MRO) of sand dunes that are round. Some are nearly perfectly circular. How did they form?

MRO took the images with its High-Resolution Imaging Experiment (HiRISE) camera on November 22, 2022. The University of Arizona also published them on their HiRISE website on March 2, 2023.

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Round sand dunes on Mars

The dark, circular dunes are along the edge of a larger field of dunes that have more irregular shapes. They kind of look like polka dots. As Alfred McEwen wrote on the HiRISE website:

Sand dunes of many shapes and sizes are common on Mars. In this example, the dunes are almost perfectly circular, which is unusual. They are still slightly asymmetrical, with steep slip faces on the south ends. This indicates that sand generally moves to the south, but the winds may be variable. This is part of a series of images to monitor how frost disappears in the late winter; this observation appears to be free of frost. A previous image shows when the surface was covered by frost.

The resolution of the posted image is 25 centimeters (9.8 inches) per pixel. Whereas, in the original image, it is 30.3 centimeters (11.9 inches) per pixel. The sand dunes are inside a crater in the Utopia Planitia region in the northern hemisphere. The unnamed crater, near Renaudot Crater, is just north of Syrtis Major.

Orbital view with large dark irregular and circular shapes at top of image, and lighter ridges at bottom.
View larger. | This context image shows the larger region around the circular sand dunes. The smaller round sand dunes are above the top edge of the larger dune field. Image via NASA/ JPL-Caltech/ University of Arizona.

Seasonal frost changes

NASA spotted the unusual sand dunes while monitoring the region for seasonal changes in frost patterns. The image showing the dark dunes reveals little, if any, frost on the ground. A previous image, however, shows the ground, including the dunes, covered in a thin layer of frost.

Perhaps surprisingly, even with its very thin atmosphere, both frost and sand dunes are common on Mars. Indeed, orbiters, landers and rovers have all seen thin layers of water-ice frost on the Martian surface. The Viking landers, in fact, photographed both frost and sand dunes in the 1980s.

MRO has been surveying Mars since 2006. It studies the Martian atmosphere, surface and geology. Likewise, the HiRISE camera onboard has taken thousands of high-resolution images of the planet and its two moons, Phobos and Deimos.

Also, in 2019, NASA’s Mars Odyssey orbiter saw hexagonal-shaped sand dunes. Mars can be a weird place, indeed!

Bottom line: NASA has just released a new photo, taken by the Mars Reconnaissance Orbiter, of intriguing round sand dunes on Mars. How did they form?

Via Jet Propulsion Laboratory


March 10, 2023

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