Permanently underground 80 meters!Nature: The first radar detection result of the "Zhu Rong" Mars car is released

Text ｜ "China Science News" reporter Feng Lifei

On September 26, the first radar detection results implemented by the "Zhu Rong" Martian car in the utopian plains were released, published in "Nature" magazine, which was noticeable.

China is the first country in the world to carry out inspection radar detection on outdoor celestial bodies.

So far, human beings have conducted four inspection radar detection on the earth's celestial bodies, three of which are from China.

The first two were my country Chang'e III and Chang'e IV, which first realized fine detection of the front and back of the front of the moon for the first time.

What are the stories behind this study? How do scientists complete the first batch of radar data analysis of the first Mars detection task in my country? Which Mars evolutionary secrets can radar detection tell us? The China Science News interviewed the Mars Research Team of the Institute of Geology and Earth Physics (hereinafter referred to as the Geological Earth) of the Chinese Academy of Sciences.

The "Zhu Rong" Mars car conducted a inspection radar survey in the utopian plains, revealing the fine underground structure and physical information of the region. Deng Jun drawing

"A happy thing"

In mid -August 2021, Wu Fuyuan, the academician of the Chinese Academy of Sciences, the then director of the Geological Earth, the academician of the Chinese Academy of Sciences, and the first -time chief scientist of the Mars Exploration Task Pan Yongxin to integrate the advantages of the entire institute for the first time, and launched the centralized centralization of construction.

Chen Ling, the person in charge of the team, Chen Ling, a researcher at the Geological Earth, and colleagues' work rhythm immediately switched to the "sprint" mode.

The task in front of it is undoubtedly a glorious mission given by the times, but there is no precedent to follow the radar detection in Mars, and the data analysis needs to be particularly cautious.

The aerospace load is constrained by power consumption, volume and weight, and cannot be repeatedly observed like the ground, resulting in the signal -to -noise ratio of its original data is usually very low.

How to extract the effective reflex information of the underground structure from it has become the first difficulty in the research team. The team's group strategies, repeatedly judged, and proposed a reasonable solution to identify and extract valid signals.

Chen Ling introduced to the "China Science News" that there is a distance of dozens of centimeters between the "Zhu Rong" radar antenna and the fire watch. The transmitting signal and reflex signal will cause strong interference after spreading in the Martian atmospheric media, covering some underground information.

At the same time, the radar energy penetration will become weaker and weaker. How to extract weak information from the deep part in noise interference is also a difficult problem.

In the research team, researchers with Chang'e III and Chang'e -4 radar detection data processing and analysis experience sharing experience with you. Starting from mid -October, the actual data analysis has finally unlocked the radar "password" after a month and a half consecutive combat, and has obtained the dream of a dreamed of high -quality signal section.

At the same time, the members of the other team continued to dynamically interpret the geological activities that the radar data may be reflected.

In the team of three generations of scientific researchers in this old and young, the elders took the helm and made suggestions; young people struggled forward and full of energy.

In order to ensure the reliability of the results, everyone has been divided into multiple independent groups to carry out the processing work to ensure the rationality and reliability of the processing process. This lays a solid data foundation for the subsequent geological interpretation.

Hard work pays off. In the early morning of November 30, 2021, as Chen Ling pressed the confirmation of the sending key on the webpage, the research team was cast out after more than a month of analysis, drawing, and writing.

On December 6, one week later, they received a reply from the editor -in -chief of "Nature". This makes everyone in the team very happy.

"It is a happy thing to be able to participate in my country's first Mars Exploration Program Tianwen No. 1." As a young researcher in the team, Wang Xin, the first author of the paper, and the associate researcher of the Geology Earth The most advanced science and technology resonance and pride in the same frequency of science and technology are also proud of the efficient and pleasant cooperation between team members.

Decoding ancient basin geological structure

Mars is a very obvious planet. "From the perspective of the terrain, its south is high and north is low. From the geological point of view, the south is relatively old geological structure and the north is relatively young." Chen Ling introduced. But the bonus border is relatively close, and the geological phenomenon observes is relatively young.

According to reports, among the two sedimentation sections of 0 to 80 meters detected by the "Zhu Rong" radar underground, the sedimentation sequence of 30 ~ 80 meters in a deeper part may belong to the Mars Late West (about 3.5 billion ~ 3.2 billion years ago) in the northern low land deposition. Studies at home and abroad believe that it is mainly related to the relatively strong flooding activities at the time.

In contrast, the shallow sedimentation section of the 10-30 meters detected by the radar is younger than the Western discipline.

The research team speculates that its formation background may include small flood events, long -term weathering, and repeated impact.

"The upper layer sedimentary order is similar to the lower layer, and the (particle size) are thin and thick, but it is only 20 meters thick, and the energy of the radar reflection is not as strong as the lower layer. Therefore, you can use a relatively short small flood activity to explain. "Chen Ling said.

At the same time, as the upper sedimentation sequence is closer to the fire watch, the researchers believe that just like the similar phenomenon observed in the Martial Mars landing area in the moon and the American "Insight" of the United States, it can also be explained by weathering or impact. In these processes, the sedimentation sequence that becomes upward due to gravity. Researchers also further judged that there is no evidence of liquid water within 80 meters in the shallow part of the area today.

"First of all, the energy of radar waves will be attenuated rapidly when it encounters liquid water, and the energy of the radar wave is relatively stable. Activity is less than 9; in addition, the "Zhu Rong" (25 degrees north latitude) and the United States 'Phoenix' (68 degrees north latitude) thermal simulation results also show that liquid water is difficult to stabilize in the shallow ground underground in the area. "Chen Chen." Chen Chen. "Chen Chen." Chen Chen. "Chen Chen." Chen Chen. " Ling said.

However, based on the current data does not exclude the shallow water within 80 meters, the existence of salt and ice form, the dielectric constant of this type of substance is equivalent to the deposition material; Because there are young "barriers to impact pits" near the landing area of ​​10 million years, that is, when the meteorite impacts, the deep fluid splashes the impact pit on the periphery to form a lotus leaf -shaped edge.

These studies are due to the rapid development of my country's outreach radar detection technology and equipment. Zhang Jinhai, a co -author and researcher at the Geological Earth Institute, said that the "Zhu Rong" carries the detection radar of two frequency bands. Among them, low -frequency radar can detect the structure of about tens of meters to 100 meters underground, while high -frequency radar It can detect a more fine structure of about 5 meters underground at a resolution of centimeters.

The exploration area of ​​the "perseverance" in the United States is the edge of the Jezuro's impact on the pit, and the actual maximum detection depth of its radar is 15 meters.

In contrast to the powerful function, the "body" of the "Zhu Rong" high -frequency band radar is very mini, with a total weight of only 6.1 kg.

According to Zhang Jinhai, the "Zhu Rong" radar load is designed and manufactured by Fang Guangyou, a researcher at the Chinese Academy of Sciences Air Heaven Information Innovation Research Institute as the relevant load carried by Chang'e III and Chang'e 4.

It is worth noting that Liu Yang, a co -author of the paper and researcher at the National Space Science Center of the Chinese Academy of Sciences, published in "Scientific Progress" in May this year in the "Zhu Rong" short -wave infrared spectrum and navigation terrain camera data. There are signs of water activities nearby, and the results of this study are confirmed by each other.

Will do better in the future

For the latest research results, the research team chose to publish in the form of "open acquisition". Chen Ling said: "This is to let more people understand the results of China's first Mars detection plan."

Chen Ling said that in the next step, there are many jobs to do around Mars radar detection. In addition to the changes in the depth of focusing the radar reflection characteristics, the horizontal changes of its reflection characteristics also need to be analyzed.

At the same time, the dielectric constant given by this study is only a parameter of the medium nature. Other properties, such as attenuation and changes in the frequency of frequency, need to be made. In addition, observation data needs to be better understood, and the combination of theoretical imitation should be further strengthened.

In order to cope with the extremely low environmental temperature in the sand and dust, the "Zhu Rong" was transferred to the dormant mode in May this year, and it is expected to resume normal work around December.

"As more data is continuously collected and analyzed, our understanding of Mars will become more and more deeper. At the same time, with the accumulation of national deep space detection experience, we will definitely do better in the future." Chen Ling said.

not

"China Science News" (2022-09-27 The first edition of the original title "Perspective 80 meters, they unlock the radar data" password ""))

not

Edit | Zhao Lu

Capture | Guo Gang

- END -