GEOGRAPHY

Zhurong discovered evidence of the ancient oceans of Mars


On May 18, an international research team led by Xiao Long, a professor at the School of Earth Sciences of China University of Geosciences (Wuhan), found petrological evidence of marine sedimentary rocks on the surface of Mars for the first time by comprehensively analyzing the scientific data obtained by the multispectral camera on the Zhurong rover, proving that there was once an ocean in the northern part of Mars. The relevant research results were published in the National Science Review under the title “Evidence of Marine Sedimentary Rocks in the Utopian Plain: Observations by the Zhurong Rover”.

Zhurong route map and patrol area terrain. Photo courtesy of the research group

Sketch of rocks and sedimentary layers observed by Zhurong, rock number Sol50-08. Photo courtesy of the research group

The current Mars is cold and dry, lacking water and traces of life, but the Martian environment hundreds of millions of years ago may be very different. Past studies have proved that there was a large amount of liquid water on Mars in the early days, and the paleoocean hypothesis has been proposed through geomorphological analysis and numerical simulation, suggesting that the paleoocean region has formed a special marine sedimentary geological unit, known as the Northern Wilderness Group, but lacks the support of in situ exploration data. As a result, the existence of oceans in the northern plains of Mars has been a bone of controversy.

In 2021, the “Zhurong” rover carried by China’s Tianwen-1 Mars mission successfully landed on the southern edge of the Utopian Plain in the eastern part of the northern plain of Mars, located in the northern wasteland group near the ancient coastline proposed by predecessors, providing an opportunity to verify the existence of paleomarine sedimentation.

Since landing, Zhurong has been heading south toward potential coastline areas and observing the exposed Northern Heath Formation formations along its way. Over the past 12 months, Zhurong has traveled about 1,921 meters, using different imaging and analysis systems to make detailed in-place observations of outcrops and surface rocks, of which navigation and terrain cameras have obtained 106 sets of panoramic images detailing the surface morphology and structural features of many rocks near Zhurong’s route.

“We looked at the photos transmitted by the rover’s on-board camera and found that the development stratigraphic structure of these exposed rocks is significantly different from the common volcanic rocks on the surface of Mars, and also different from the stratigraphic structure formed by aeolian sedimentation, and the characteristics of bidirectional water flow indicated by these stratigraphic knowledge are consistent with low-energy tidal flows in the Earth’s coast-shallow sea environment.” Xiao Long said.

Since the observed rocks are located in the Zhurong patrol area, the research team named the geological unit they represented “Zhurong section”. In the study, the team found that the rocks in the section usually retain a local lens-like interlaced structure, mainly a variety of small interlaced layers, accompanied by a small number of lenticular flattened layers and sedimentary structures of small waterway structures. Among them, the layers that make up the interlaced layer are stacked and tilted in two opposite directions, indicating a two-way paleoflow environment.

In addition, due to the large differences in thickness and particle size of the layer system in different directions, it indicates that there is a difference in the intensity of paleowater flow in both directions. This bidirectional flow pattern is usually formed by fluid action with periodic changes in flow direction and is not common in aeolian and fluvial environments, but is common in the Earth’s coastal-shallow marine environment. Compared to Earth, Mars has only two small moons, giving it a low-energy tidal system on its surface, in which only small-scale stratigraphic structures can be formed. In addition, the substrate and sedimentary structures identified in the study have evidence to support their flow water rather than aeolian deposits.

The observations of Zhurong rocks in this study are the first evidence to date to support the presence of paleooceans in the northern plains of Mars. The location of the Zhurong landing site suggests that the observed sedimentary formations may have formed during the retreat of the paleooceans of the northern plains.

These sedimentary formations, discovered in the Northern Wastelands Formation, shed new light on reshaping the history of Mars. “In the future, Zhurong’s in-depth exploration and sampling return of the region will deepen our understanding of the habitability of Mars and the preservation of traces of life.” Xiao Long said.

It is reported that Xiao Long and Professor Huang Jun of China University of Geosciences (Wuhan) are the co-first authors of the paper, and Xiao Long and Professor Tim Koski of China University of Geosciences (Wuhan) are the co-corresponding authors of the paper. (Source: China Science News, Wen Caifei, Wang Junfang, Liang Ruihua)

Related paper information:https://doi.org/10.1093/nsr/nwad137



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