Zhu Rong found signs of recent water activity on Mars

On May 12, the international journal Science Advances published the new results of zhurong.

Using data from the Zhurong rover of Tianwen-1’s first Mars mission, the research team of the National Space Science Center of the Chinese Academy of Sciences found a lithified plate-like hard shell layer in the landing area with a relatively young geological age, rich in minerals such as aqueous sulfates, and its formation process may be related to groundwater fluctuations.

The discovery suggests that water activity on Mars during the Amazonian period may have been more active than previously thought, and that the Zhurong landing area, as well as the vast area of the northern plains of Mars, may contain large amounts of available water in the form of aqueous minerals that could be used by in situ resources for future manned Mars exploration.

Zhu Rong’s trajectory (Source: National Space Science Center, Chinese Academy of Sciences)

Special bright colored rocks

On May 15, 2021, the “Zhurong” rover successfully landed in the southern region of the utopian plain, and as of now, it has traveled for 1 year in the utopian plain area of the northern lowlands of Mars, traveling 2 kilometers, and obtaining a large amount of valuable scientific exploration data.

Among them, the short-wave infrared spectral microscopy imager carried by the “Zhurong” can analyze minerals and rock composition on the surface of Mars, while the navigation terrain camera, which is the “eye” of the Mars rover, can calibrate and determine the true situation of the Martian surface by taking wide-angle pictures and the ground pictures taken by the orbiter flying in space, guiding the rover’s forward route, and determining the exploration target.

From the data generated by these two instruments, Liu Yang, a researcher at the State Key Laboratory of Space Meteorology at the National Space Science Center of the Chinese Academy of Sciences, and collaborators, found a unique plate-like bright colored rock.

Because of heat and weathering, these brightly colored plate-like rocks are usually partially covered with dust and soil, with the rest showing peeling surfaces.

Lithological hard shell (Image source: National Center for Space Science, Chinese Academy of Sciences)

There is an aqueous substance in it

Curious, Liu Yang et al. analyzed the short-wave infrared spectra of these bright-colored rocks. They were surprised to find that this was an aqueous mineral that had not been identified in the region by previous orbital data.

Previously, orbital remote sensing data analysis showed that a variety of geomorphological features distributed around the Zhurong landing site indicated that the utopian plains once had a large number of volatile points. However, due to spatial resolution and coverage, orbital remote sensing data have not found aqueous minerals near the landing zone, which makes the formation mechanism of such landforms and the nature of water activity in the area a mystery.

The new discovery made Liu Yang and others extremely excited. Based on the rock’s absorption characteristics of the spectrum, they speculated that that particular bright-colored rock contained water silicon or aqueous sulfates.

“This is the first time in the world that aqueous minerals have been detected in situ on Mars using the short-wave infrared spectrometer on the rover.” Liu Yang told China Science Daily.

However, at the same time of excitement, another question mark appeared in the minds of Liu Yang and others – how did this unique bright white rock appear?

Associated with groundwater fluctuations

Looking at these particular plate rocks, the research team thought of the fractured rock morphology observed by the American Mars lander “Viking One” in the landing area.

However, the hard shell layer of the Viking One landing zone is relatively brittle and thin, which may be formed by the long-term interaction of water vapor in the atmosphere and the soil on the surface of Mars. The hard shell of the Zhurong landing site appears to be more resistant to erosion and forms a thick layer in the loose surrounding soil.

“This requires a lot of liquid water, which cannot be formed by water vapor in the atmosphere alone.” Liu Yang said.

At the same time, the team also found a detail: there were no obvious traces of surface runoff or river channels in the landing area, and no fluffy surfaces and salt frost residues formed by the evaporation of water bodies were found around the tour route. From this, they ruled out the possibility of large-scale water activity on the surface.

So there is only one possibility left: groundwater.

On the basis of various information materials, the research team proposed the formation mechanism of bright rocks: the soil weathering layer before the sedimentary period, during the rise or infiltration of salt-rich groundwater, underwent cementation and lithification, forming the observed plate-like rocks.

“Salt cements precipitate from pores or groundwater close to the submersible surface, with active evaporation and aggregation. Intermittent fluctuations in the water table may thicken the hard shell further and form a layered structure. Subsequently, the topsoil covering the hard shell is eroded and eroded, exposing the erosion-resistant hard shell. Liu Yang said.

Schematic diagram of the formation process of lithified hard shell rich in sulfates in zhurong landing area (Source: National Space Science Center, Chinese Academy of Sciences)

Martian water activity is longer than expected

The geological age of Mars is divided into four stages: pre-Noahic, Noahic, Western and Amazonian, of which the Amazonian period is from 3 billion years ago to the present.

The landing area of Zhu Rong is located in the young and cold and arid Amazonian strata, and it is precisely because of the cold and dry that it is believed that the scope and extent of liquid water activity during this period is extremely limited.

But the discovery suggests that Mars’ water activity during the Amazonian period may have been more active than previously thought, challenging conventional wisdom about the evolutionary history of Mars’ climate and environment. (Source: China Science Daily Ni Sijie)

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