China’s Zhurong rover peered deep below the surface of Mars, finding evidence of two major floods that have likely shaped the region the rover has been exploring since landing in May 2021.
An analysis published in Nature today is the first result from Zhurong’s radar imager, which can probe up to 100 meters below the surface. “It’s a very interesting paper, and I was particularly impressed with how deep they can see with this radar,” says Svein-Erik Hamran, a planetary scientist at the University of Oslo, who analyzed the only data. previous ground penetrating radar. used on the planet, collected by NASA’s Perseverance rover.
The story of the Zhurong landing site – on Utopia Planitia, vast plains in Mars’ northern hemisphere – has intrigued scientists. Some have speculated that water or ice was once a feature of the landscape. Observations from space have identified sedimentary deposits that suggest the region was once an ancient ocean or submerged by huge floods, and geological features, such as pitted cones, resemble structures formed by water or ice. In May, researchers analyzed infrared images of the landing site taken by China’s Mars orbiter, Tianwen-1, and found hydrated minerals that could have formed when groundwater passed through the rock or the ice melted.
But the area could also have been covered in lava, hiding some of these hydrological processes underground. Eruptions of the Elysium Mons volcano east of the landing site, or other volcanic activity, could have blanketed the region with magma, as has been observed in other parts of the Utopia Basin. By studying radar data, researchers hope to understand what happened and whether water or ice might still be hiding under the rocks. “We want to know what’s going on below the surface,” says study co-author Liu Yang, a planetary scientist at the National Center for Space Science in Beijing.
below the surface
Zhurong is the first Chinese rover on the Red Planet, and it explored the southern part of Utopia Planitia. The rover’s ground-penetrating radar transmits high-frequency radio waves that can penetrate the surface to a depth of between 3 and 10 meters, and low-frequency waves that can reach up to 100 meters underground but offer lower resolution . The study authors analyzed low-frequency data taken between May 25 and September 6 over more than 1,100 meters of terrain as Zhurong moved south of its landing site. Radar signals reflect off materials below the surface, revealing their grain size and ability to hold electrical charge. Stronger signals generally indicate larger objects.
The radar found no traces of liquid water up to 80 meters, but it detected two horizontal layers with interesting patterns. In a layer between 10 and 30 meters deep, the team reports, the reflection signals strengthen with increasing depth. The researchers say this is likely due to larger boulders resting at the base of the layer and smaller rocks settling on top. An older, thicker layer between 30 and 80 meters deep showed a similar pattern.
The oldest layer is likely the result of rapid floods that transported sediment to the region more than three billion years ago, when there was a lot of aquatic activity on Mars, explains the co- author Chen Ling, seismologist at the Institute of Geology and Geophysics. , Chinese Academy of Sciences, Beijing.
The top layer may have been created by another flood around 1.6 billion years ago, when there was a lot of glacial activity. Chen says the top layer is unlikely to contain intact lava flows because it has a smaller ability to hold electrical charge than would be expected for intact volcanic rocks. Additionally, the researchers saw no sudden changes in stratification, which would be expected when lava flows encounter sedimentary materials.
Volcanic or sedimentary?
But, says Chen, it’s possible that a thin layer of lava once covered the upper layer and it gradually broke down into smaller pieces. Radar data alone cannot definitively tell whether the material is sedimentary or volcanic, says Xu Yi, a planetary scientist at Macao University of Science and Technology.
Radar data is good at indicating the stratification and geometry of underground material, but not so good at determining its composition, including whether the material is ice or rock, Hamran says. Often researchers rely on other clues, such as rocks emerging from the surface, to build a picture of past events, he says. The authors say they cannot rule out the possibility that the region contains buried salt ice.
Other radar results are expected from the mission, including data taken during Zhurong’s continuous traverse of Mars, results of high-frequency radar measurements already made, and orbital radar observations of Tianwen-1, which penetrate deep into the planet. . They could help clarify the details of the terrain. “This is just the first step,” Ling said.
This article is reproduced with permission and has been first post September 27, 2022.