Not sure if there's water on Mars? Maybe we can dig a well there!

It is unlikely that there is liquid water underground on Mars, but there may be salt ice.

Is there water on Mars? When the telescope was first invented, people saw many ditch-like structures on Mars. So many people thought that they were canals of the Martians, and even made news about the Martians invading the Earth. However, now we know that Mars is a dry planet, and the living conditions are far worse than those on Earth. Not to mention intelligent life, even elementary life has not been found. However, it is still possible that there was water on Mars in the past, and there may still be water now - just not on the surface, but underground.

Recently, the Mars research team of the Institute of Geology and Geophysics of the Chinese Academy of Sciences held a media interpretation meeting to interpret the latest research results of the "Tianwen-1" Mars exploration (https://www.cas.cn/zkyzs/2022/09/364/zyxw/202209/t20220927_4849010.shtml). There are two main results: First, the surface of Mars may have been transformed by water; second, it is unlikely that there is liquid water underground on Mars, but there may be salt ice.

Explain in detail. On May 15, 2021, the "Zhurong" Mars rover carried by my country's first Mars exploration mission "Tianwen-1" successfully landed in the pre-selected landing area in the southern part of Utopia Planitia, starting patrol and exploration work. Utopia Planitia is the largest impact basin on Mars. It may have been an ancient ocean, indicating that there may have been a habitable environment on Mars in its early days. How did the geology here evolve? What kind of underground structure does it have today? Is there still water or ice? The sub-surface detection radar of the "Zhurong" Mars rover can perform fine imaging of the shallow underground structure in the patrol area, allowing us to make breakthrough progress on these issues.

From a broader perspective, humans have conducted a total of four patrol radar detections on extraterrestrial bodies so far, three by China and one by the United States. Yes, China has more than the United States! There were two patrol radar detections on the moon, with my country's Chang'e 3 and Chang'e 4 respectively achieving detailed detection of the shallow surface structures on the front and back of the moon. There were two patrol radar detections on Mars, with the United States' "Perseverance" and my country's "Zhurong" successively launching patrol radar detections on Mars in 2021. The detection area of ​​"Perseverance" is the edge of Jezero Crater, with an actual maximum detection depth of 15 meters. The detection area of ​​"Zhurong" is the southern part of Utopia Planitia, with a wide radar band and an actual maximum detection depth of 80 meters.

My senior sister from the University of Science and Technology, Chen Ling, a researcher at the Institute of Geology and Geophysics of the Chinese Academy of Sciences, introduced at a media interpretation meeting (Is there water on the shallow surface of Mars? The latest discovery by a Chinese female scientist) that the research team conducted an in-depth analysis of the low-frequency radar data of the "Zhurong" Mars rover in the first 113 Martian days (a Martian day is a "day and night" on Mars, about 2 minutes longer than on Earth), with a detection length of 1,171 meters. They obtained high-precision structural stratification images and stratigraphic physical property information within 80 meters of the shallow surface of Mars, and found that under the several-meter-thick pyrosol layer in the southern region of Utopia Planitia, there are two sets of sedimentary sequences that become finer upwards, which may reflect multiple periods of pyrosol modification related to water activities over the past 3.5 billion to 3.2 billion years.

The first sequence is located about 10-30 meters below the surface of the fire, containing more stones, whose grain size gradually increases with depth, which may come from short-term floods, long-term weathering or repeated meteorite impacts about 1.6 billion years ago. The second sequence is located about 30-80 meters below the surface of the fire, and its stone grain size is larger (up to meter level) and more chaotically distributed, reflecting an older and larger-scale fire surface modification event. Based on the statistical dating results of previous impact craters, it is speculated that this modification event may have occurred 3.5 billion to 3.2 billion years ago and was related to large-scale flood activities in the southern part of Utopia Planitia.

Another major goal of this study is to detect whether there is groundwater or ice in the southern part of Utopia Planitia today. The results of low-frequency radar imaging show that the reflection signal intensity is stable within the depth range of 0-80 meters on the surface of the fire, and the medium has a low dielectric constant, which means that there is no water-rich layer below the patrol path of the Mars rover. Further thermal simulation results show that liquid water, sulfate or carbonate brine is difficult to exist stably within 100 meters underground in the landing area of ​​the "Zhurong" Mars rover. However, the possibility of the existence of salt ice cannot be ruled out at present, nor can the possibility of liquid or solid water in deeper underground space be ruled out. These need to be studied in the future.

Chen Ling said that this study revealed the fine structure and physical properties of the shallow surface of Mars today, and provided observational evidence that water activities may have existed on Mars for a long time. The study showed that under the overall background of the evolution of Mars becoming dry, there was a complex process of surface transformation related to water activities about 3.5 billion to 3.2 billion years ago, which changed people's traditional understanding of the evolution of Mars. These 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. Yes, if we don't pay attention to protecting the environment, the Earth will become as lifeless as Mars in the future.

At the same time, this study also raises a series of new scientific questions: What is the structure of Mars below 80 meters? How deep is the water on Mars? Which areas have water? How long will the "water" influence on Mars last? These provide ideas and directions for future research, and maybe you can contribute to it.