China News Service, Beijing, September 26 (Reporter Sun Zifa) Mars is considered to represent the "future of the earth" in terms of evolution, so the related exploration research on Mars has attracted much attention for a long time.

What is the structure of the surface of Mars?

Is there solid or liquid water?

What evolutionary process has Mars geology experienced?

… There is a great deal of interest in these questions, both by scientists and by the general public.

  Using the radar data obtained from the inspection and detection of the Mars rover "Zhurong" carried by China's first Mars exploration mission Tianwen-1 successfully landed on Mars in May 2021, the Institute of Geology and Geophysics of the Chinese Academy of Sciences (Institute of Geology and Geophysics, Chinese Academy of Sciences) and the National The latest research completed by the Space Science Center, Peking University and other cooperative teams found that in the southern part of the Utopia Plain, where the "Zhurong" rover's landing area is located, there are two sets of upwardly thinning sedimentary sequences under the regolith with a thickness of several meters above the fire surface. It may reflect that there have been multiple stages of fire table modification related to water activity in the region since about 3.5 billion to 3.2 billion years ago.

The corresponding author of the paper, researcher Chen Ling of the Institute of Geology and Earth Sciences, Chinese Academy of Sciences, explained the latest research results on Mars by popular science.

Photo by China News Agency reporter Sun Zifa

  The research team emphasized that there is no direct evidence of the existence of liquid water within 80 meters below the current fire surface in the research area in the southern Utopia Plain of Mars, but it does not rule out the possibility of the existence of solid salt ice, and also does not rule out the existence of liquid or solid water in the deeper underground space of Mars. possible.

  The results of this important progress in the field of Mars exploration research were published online in the internationally renowned academic journal "Nature" on the night of September 26, Beijing time.

On the eve of the publication of the paper, the Mars research team of the Institute of Geology and Earth Sciences of the Chinese Academy of Sciences held a media interpretation meeting on the "Zhurong" patrol radar in Beijing to reveal the superficial structure of Mars, to popularize the scientific research results of Mars that they cooperated with.

  The corresponding author of the paper and researcher Chen Ling from the Institute of Geology and Earth Sciences of the Chinese Academy of Sciences introduced that the Utopia Plain is the largest impact basin on Mars, and it may have been an ancient ocean, indicating that there may have been a habitable environment on Mars in the early days.

The detailed information on the subsurface structure and physical properties of Mars is the key basis for studying the evolution of Martian geology and its habitable environment, and it is an important part of Mars exploration.

The "Zhurong" subsurface detection radar carried by China's Tianwen-1 Mars rover can perform fine imaging of the subsurface structures in the inspection area, deepening people's understanding of key scientific issues such as the evolution of the Utopian plain and the distribution of groundwater/ice.

Group photo of representatives of the latest Mars research results team of the Chinese Academy of Sciences.

Photo by China News Agency reporter Sun Zifa

  So far, humans have carried out 4 patrol radar detections on extraterrestrial celestial bodies, including China's Chang'e-3 and Chang'e-4, which have successively achieved fine detection of the superficial structures on the front and back of the moon; the American "Perseverance" and China's "Zhurong" "The rover will start Mars roaming radar detection on the edge of the Jezero crater and the southern part of the Utopia Plain in 2021.

Among them, the subsurface detection radar carried by the "Zhurong" rover is the world's first rover radar detection on the Mars Utopia Plain. Its radar frequency band is wide, and the actual maximum detection depth is 80 meters. After the release of the National Space Administration, it provides a solid data guarantee for scientists to carry out Mars-related research.

  Chen Ling said that in this latest study, the research team analyzed the first 113 Martian days (one Martian day is the "day and night" on Mars, which is about 2 minutes longer than Earth), and the "Zhurong" probe with a length of 1,171 meters. In-depth analysis of the low-frequency radar data of the Mars rover was carried out to obtain high-precision structural layered images and stratigraphic physical property information in the range of 80 meters on the surface of Mars. It was found that there are two sets of upwardly thinning deposits under the several-meter-thick fire soil layer in the southern area of ​​the Utopia Plain. The sequence may reflect the multi-stage fire table transformation process related to water activity since about 3.5 billion to 3.2 billion years.

  The first sequence is located about 10-30 meters below the surface of the fire, and contains many rocks, the particle size of which gradually increases with depth.

Short-term floods, long-term weathering, or repeated meteorite impacts since about 1.6 billion years ago may have led to the formation of this upwardly thinning sedimentary sequence.

  The second set of sequences is located about 30-80 meters below the fire surface, and its rocks are larger in size (up to meter scale) and more chaotically distributed, reflecting an older and larger-scale fire surface transformation event.

Based on the statistical dating results of previous impact craters, it is speculated that this transformation event may have occurred 3.5 billion to 3.2 billion years ago, and was related to the large-scale flooding activities in the southern part of the Utopia Plain.

A schematic diagram of the popular science interpretation of the Mars research results.

Photo courtesy of Institute of Geology and Earth Sciences, Chinese Academy of Sciences

  Chen Ling pointed out that another main goal of the "Zhurong" Mars rover's subsurface detection radar is to detect whether there is groundwater/ice in the southern part of the Utopia Plain.

The low-frequency radar imaging results of this study show that the reflected signal strength of the fire surface is stable in the depth range of 0-80 meters, and the medium has a low dielectric constant, which excludes the possibility of a water-rich layer under the rover's patrol path.

The results of further thermal simulations also show that it is difficult for liquid water, sulfate or carbonate brine to exist stably within 100 meters of the landing area of ​​the "Zhurong" rover, but the possibility of the existence of salt ice cannot be ruled out at present. Excluding the possibility of the existence of liquid or solid water in deeper underground spaces requires more continuous and in-depth exploration and research in the future.

  She and the research team said that the original results obtained by Chinese scientists using the scientific data of the first Mars exploration mission of China's Tianwen-1 revealed the fine structure and physical characteristics of the current surface of Mars, and provided observational evidence that water activities may exist on Mars for a long time. Among them, studies have shown that under the background of the overall arid evolution of Mars, the evolution of Mars still had a complex process of water activity-related fire table transformation about 3.5 billion to 3.2 billion years ago, which also changed people's traditional understanding of Mars evolution .

These scientific research results will provide an important basis for in-depth understanding of the geological evolution, environment and climate change of Mars, and also provide an important reference for understanding the future evolution of the earth.

A schematic diagram of the popular science interpretation of the Mars research results.

Photo courtesy of Institute of Geology and Earth Sciences, Chinese Academy of Sciences

  At the same time, the results of this research also raise a series of new scientific questions for the study of Mars evolution and structure: What is the structure below the fire surface 80 meters?

How deep is Mars with water?

Which areas have water?

How Long Does Mars' "Water" Impact Last?

These also provide new ideas and directions for future Mars exploration and research.

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