The reporter learned from the Institute of Aerospace Information Innovation of the Chinese Academy of Sciences that the research team of the moon and Mars exploration radar led by researcher Fang Guangyou of the institute found that there are multi-layered inclined sedimentary structures 10 to 35 meters underground in the Zhurong landing area in the southern part of the Utopian Plain in the northern hemisphere of Mars. These geological characteristics are highly similar to Earth's coastal sediments, providing the most direct underground evidence to date for the existence of ancient oceans in the middle and low latitudes of Mars. The results were published in the Proceedings of the National Academy of Sciences (PNAS) on February 25, 2025 Beijing time.
Mars is regarded by scientists as the preferred target of human interstellar migration because of its similar geological characteristics, seasonal changes and circadian rhythms to Earth. Human exploration of Mars has achieved many milestones in the past few decades, but most of these discoveries are concentrated in high latitudes or polar regions of Mars where the environment is extremely cold, and debate over whether there has ever been a vast ocean in the northern lowlands of Mars has always existed, making it crucial to obtain direct evidence of the Martian ancient ocean.
△The imaginary picture of Mars 3.6 billion years ago. The blue area shows the now-disappeared ancient ocean and coastline of Deuteronilus. The orange star represents the landing point of the Zhurong rover in China. The yellow star is the landing point of the NASA Perseverance rover (Photo source: Robert Citron)
China's first Mars rover, Zhurong, landed in the southern part of the Utopian Plain on May 15, 2021. It is equipped with the Mars subsurface penetration radar developed by the Institute of Aerospace Information Innovation of the Chinese Academy of Sciences, for detection of underground structures and possible water ice. The route of Zhurong is about 280 kilometers north of the ancient marine coastline that the previous generations proposed possible, and is about 500 meters lower than the coastline at an altitude.
△Utopian plain map, Zhurong rover landing site and four possible ancient coastlines
The research team identified 76 underground inclined reflectors within a depth of 10 to 35 meters below the surface along the rover by analyzing the actual measured data of the Zhurong radar low-frequency channel. These emitters are widely distributed and uniform in space, with a coverage range of more than 1.3 kilometers. All reflectors show the characteristics of inclination toward the northern lowland direction, with an inclination angle between 6° and 20°, an average inclination angle of 14.5°, and multiple parallel distributed reflectors can be observed at different depths at the same location. These stratigraphic structures are very similar to radar imaging results of Earth's coastal sediments, and their consistency and physical properties exclude other causes such as wind-forming sand piles, lava pipelines or river alluvials. The large-scale existence of these sediments suggests that wind-wave-driven coastal transport provides a stable net inflow of silt and sand for the coastline and forms an aforementioned strata, a structure that can only be formed in a long-lasting and stable large water environment, rather than just local and transient melting.
This study not only provides key underground evidence that ancient oceans existed in the plains of Mars, but also reveals that Mars has experienced a long-term warm and humid climate period, which means that Mars has maintained temperature and pressure conditions suitable for the existence of liquid water for a long time. In addition, the dielectric properties of coastline sediments found in the study are consistent with the dielectric constants of fine and medium sand particles on Earth, which further confirms the properties of its marine sediments.
△Comparison of inclined reflections detected on Mars and Earth's oceanic sediments (A) Earth penetrating radar image of coastal sediments in Shark Bay, Australia; (B) Radar profile of Zhurong Mars subsurface penetrating radar low-frequency channel radar
△Schematic diagram of the formation process of the inclined sedimentary structure at the Zhurong landing point (A) A hierarchical structure formed under the action of tidal sedimentation; (B) As the ancient coastline retreated, liquid water disappeared and sedimentation stopped. The subsequent long-term physical and chemical weathering alters the properties of rocks and minerals, leading to the formation of the Martian surface layer. Therefore, the sediments are covered by the current Martian surface soil
The greatest significance of this discovery is to expand the evidence of Martian liquid water from the rarely visited polar regions on Mars to the middle and low latitudes that are more suitable for human activities, confirming that Mars was once habitable. If there were oceans in this area, then with climate change, a large amount of water may be stored in the form of underground ice, providing the possibility for the future water resource utilization of Mars bases and greatly reducing the construction and maintenance costs of Mars bases. In addition, these paleo-ocean sediments preserve the historical records of Mars' climate change. Studying these sediments can help us understand how Mars changed from warm and humid to cold and dry, and in turn guide humans how to transform the Martian environment and achieve long-term sustainable habitation on Mars.
(CCTV reporter Shuai Junquan Chu Erjia)
