There are mysterious polygons under the surface of Mars

There are mysterious polygons under the surface of Mars

China’s Zhurong spacecraft is equipped with a ground-penetrating radar system, allowing it to peer beneath the surface of Mars. Researchers announced new results from scans of Zhurong’s landing site on Utopia Planitia, saying they identified irregular polygonal wedges located at a depth of about 35 meters throughout the robot’s flight. Objects measure from centimeters to tens of metres. Scientists believe the buried polygons resulted from freeze-thaw cycles on Mars billions of years ago, but they could also be volcanic, the result of cooling lava flows.

A radio camera captured this “group photo” of the Chinese lander and rover Tianwen-1 on the surface of Mars. Credit: China Space Agency

The Zhurong spacecraft landed on Mars on May 15, 2021, making China the second country ever to successfully land on Mars. The gentle rover, named after the Chinese god of fire, explored its landing site, sent back images — including a selfie with the lander, taken by a remote camera — studied the Martian terrain, and made measurements using ground penetrating radar (GPR). ) a tool. Zhurong’s initial mission life was three Earth months, but it operated successfully for just over one Earth year before entering a planned hibernation state. However, no news has been heard from the vehicle since May 2022.

Researchers from the Institute of Geology and Geophysics of the Chinese Academy of Sciences who worked with Zhurong’s data said GPR provides an important complement to orbital radar explorations from missions such as the European Space Agency’s Mars Express and China’s Tianwen-1 orbiter. They said an in-situ GPR survey could provide important local details on shallow structures and their composition at a depth of about 100 meters along the rover’s path.

A, Topographic map of Utopia Planitia, showing the landing sites of the Zhurong rover, the Viking 2 lander, and the Perseverance rover. The 4 km altitude contour is shown. Four local areas (c–f) with polygonal terrain are marked with white boxes. B, The Zhurong spacecraft transits from Sol 11 to Sol 113 (HiRISE image: ESP_073225_2055). Green sections indicate the wedges of buried polygons recognized in Figure 2 (P1–P16). The purple parts indicate the interior parts of the polygons. c–f, Four representative HiRISE images of polygons in Utopia Planitia whose locations were located at: PSP_002202_2250 (c), PSP_006962_2215 (d), PSP_002162_2260 (e) and PSP_003177_2275 (f). Note the range of spatial scales of polygon sizes. The diameters of the polygons shown in c–f are averaged in Expanded Data Figure 6. HiRISE Image credit: NASA/JPL/University of Arizona.

Utopia Planitia is a large plain within Utopia, and is the largest recognized impact basin on Mars (also in the solar system) with a diameter of about 3,300 km. In total, the vehicle traveled 1,921 meters during its lifetime.

The rover’s radar detected sixteen polygonal wedges at a distance of about 1.2 kilometers, indicating a broad distribution of similar terrain beneath Utopia Planitia, the researchers, led by Li Zhang, wrote in their paper published in the journal Nature. These unearthed features were likely formed 3.7 to 2.9 billion years ago during the late Hesperian and early Amazonian eras on Mars, “perhaps as the ancient wet environment ceased. The ancient polygonal terrain, with or without erosion, was buried by processes subsequent geological.

Schematic model of the polygonal terrain formation process at the Zhurong landing site. A, The formation of cracks resulting from thermal shrinkage on the surface. B, Formation of cracks filled with water ice or soil material, causing three types of polygonal terrain (ice wedge polygons, compound wedge, and sand wedge polygons). C, Stabilization of polygonal surface terranes in late Hesperian and early Amazonian times, perhaps with the cessation of the ancient wet environment. D, The ancient polygonal terrain was buried, with or without erosion, by the deposition of covering materials in the Amazon. The image of the Martian surface was obtained by the Navigation and Terrain Camera (NaTeCam). Credit: Zhang et al.

Although polygonal terrain has been seen across several regions of Mars by several previous missions, this is the first time there have been indications of buried polygonal features.

The buried polygonal terrain requires a cold environment that may be related to the freezing and thawing processes of water and ice in southern Utopia Planitia on early Mars, the researchers wrote.

“The possible presence of water and ice needed for the freezing and thawing process in the wedges may have come from moisture migration caused by cryogenic suction from the subsurface aquifer on Mars, snow falling from the air or vapor diffusion to deposit porous ice,” he explains.

Previous research from Zhurong’s radar data indicated that multiple floods during the same time frame created several layers beneath the surface of Utopia Planitia.

While the new study suggests that the most likely potential formation mechanisms are soil shrinkage from wet sediments that have dried, producing clay cracks, shrinkage caused by cooling lava can also produce thermal contraction cracks.

In both cases, they note that a significant change in Mars’ climate was responsible for the formation of the polygon.

“The subsurface structure with capping materials covering the buried ancient polygonal terrain suggests that there was a marked paleoclimatic shift at some point afterward,” the researchers wrote. “The variation above and below a depth of about 35 meters represents a marked shift in water activity or thermal conditions in ancient Mars time, meaning that there was climate perturbation at low to mid-latitudes.”

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