China’s Zhurong rover, which landed on Mars in May 2021, has made a groundbreaking discovery using ground-penetrating radar. The rover has identified buried polygonal wedges at a depth of 35 meters on Mars’s surface. These wedges, ranging in size from centimeters to tens of meters, are believed to have formed billions of years ago due to freeze-thaw cycles or cooling lava flows.
The radar data collected by Zhurong has provided valuable insights into the shallow structures and composition within approximately 100-meter depths along the rover’s traverse. In the region where the rover landed, called Utopia Planitia, sixteen polygonal wedges were detected within a span of approximately 1.2 kilometers. This suggests that this type of terrain is widespread under Utopia Planitia.
Utopia Planitia is a large plain situated within the largest recognized impact basin on Mars and the entire Solar System, with an estimated diameter of 3,300 kilometers. The presence of these buried polygonal features indicates a cold environment, possibly associated with freeze-thaw processes and the presence of water or ice. Previous radar data from Zhurong also indicated the occurrence of multiple floods during the same time period, resulting in layers beneath the surface of Utopia Planitia.
The formation mechanism of these polygons is still being investigated. The most probable explanation is that they formed as a result of soil contraction from wet sediments drying, leading to the development of mud cracks. However, it is also possible that cooling lava caused thermal contraction cracking, contributing to their formation.
This discovery has significant implications for our understanding of ancient Martian climate. The buried polygons suggest a notable palaeoclimatic transformation and a climatic upheaval at low-to-mid latitudes during ancient Martian times. They likely formed billions of years ago during the Late Hesperian-Early Amazonian epochs, possibly signaling the end of an ancient wet environment on Mars.
The Zhurong rover has completed its exploration of the landing site and conducted measurements using its radar instrument before entering hibernation in May 2022. The data collected by Zhurong will contribute to ongoing research and provide crucial insights into the geological history of Mars.
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