Aqueous Process Record at the Zhurong Landing Site in Utopia Planitia: New Constraints on Martian Hydrological Activity.

Introduction: As one of the nearest terrestrial planets to Earth within the solar system, Mars has long been a focal point for research regarding surface aqueous activity, which is essential to understand its environmental evolution [1].  Numerous studies have been conducted on the aqueous activity history of Mars through investigations of its surface morphology and lithological/mineralogical characteristics. However, substantial controversies persist regarding the evolutionary trajectory of aqueous environments on Mars and certain hypotheses, particularly those concerning paleo-ocean existence. Consequently, sustained exploration of the Martian surface remains imperative for advancing our comprehension of its aqueous history.

Data and Method: In May 2021, the Zhurong rover safely landed in southern Utopia Planitia (109.925°E, 25.066°N), near a hypothesized ancient Mars shoreline, and performed in situ exploration [2-3]. The Zhurong rover equipped with six scientific instruments—Navigation Terrain Camera (NaTeCam), Multispectral Camera (MSCam), Penetrating Radar (RoPeR), Surface Composition Detector (MarSCoDe), Magnetometers (RoMAG), and Mars Climate Station (MCS) [3]. It has travelled 1,921 meters southward and provided novel scientific data for investigating aqueous activity on Mars. Processing and analysis of these data have yielded a series of significant findings, advancing the understanding of Martian hydrological processes.

Results and discussion:

(1) Evidence for a Hesperian Paleo-Ocean​​

The paleo-ocean hypothesis postulates the existence of an early Martian ocean during the Hesperian period [4-7], though this remains controversial. Xiao et al. [8] conducted comprehensive analyses of MSCam and NaTeCam image data and identified sedimentary bedding structures exhibiting bidirectional flow patterns, demonstrating remarkable similarity to terrestrial shallow marine depositional environments. These findings provide petrological evidence that supports the presence of a Hesperian paleo-ocean in Utopia Planitia. Furthermore, through integrated analysis of Zhurong's radar data, Li et al. [9] identified multiple inclined sedimentary strata at depths of 10-35 meters beneath the landing site. These subsurface structures show striking analogies to coastal depositional sequences on Earth, offering structural evidence for an ancient ocean in the mid-low latitudes of Mars.

​(2) Evidence for Prolonged Aqueous Activity During Late Hesperian​​

Zhurong's radar RoPeR acquired high-resolution stratigraphic profiles of the shallow subsurface (~80 m depth) in southern Utopia Planitia. Li et al. [10] demonstrated that the sedimentary sequence between 30-80 m depth likely records large-scale flooding events during the late Hesperian to early Amazonian transition, while the 10-30 m interval may represent products of ephemeral floods, prolonged weathering, or impact-generated processes. These observations reveal multiple episodes of aqueous activity persisting through the late Hesperian.

(3) Evidence for Early/Middle Amazonian Aqueous Activity​​

Zhurong's landing site in southern Utopia Planitia (characterized by low latitude and elevation [11]) represents an optimal location for preserving records of stable surface water. Utilizing data from NaTeCam, the MarSCoDe employing Laser-Induced Breakdown Spectroscopy and the Telescopic Micro-Imager, along with meteorological measurements from MCS, Zhao et al. [12] identified signatures of saline aqueous activity (~760 Ma) and contemporary water vapor cycling in the exploration area.

(4) Late Amazonian Aqueous Activity and Climatic Evolution​​

In the current Martian environment, hydrological activity is predominantly manifested in polar cap oscillations, with liquid water being exceptionally rare [1]. Zhurong's investigations revealed lithified slab-like crusts enriched in hydrous sulfate minerals. Liu et al. [13] interpreted these crusts as products of groundwater upwelling or capillary evaporation, where saline minerals cemented regolith before lithification, indicating more vigorous late Amazonian hydrologic activity than previously recognized.

Qin et al. [14] conducted comprehensive analyses of dune surface morphology and composition using NaTeCam, MSCam, and MarSCoDe data. They identified diagnostic features including duricrusts, desiccation cracks, granulated surfaces, polygonal ridges, and linear features of water activity. Spectral analyses further revealed the presence of hydrous sulfates, opaline silica, and hydrous iron oxides - definitive mineralogical indicators of liquid water activity in low-latitude regions, suggesting a more humid contemporary Martian environment than conventional models predict.

Liu et al. [15] performed synergistic analyses combining high-resolution orbital imagery with rover-based observations to reconstruct aeolian depositional history. Their investigation of dune morphology, surface textures, and composition revealed stratigraphic evidence for a significant wind regime shift. This climatic transition correlates with ice-dust layer records in mid-high latitudes, suggesting a global "glacial-interglacial" transition approximately 400 ka ago, potentially driven by obliquity variations that redistributed volatiles from mid-low latitudes to polar regions.

The water-related features observations acquired by the Zhurong rover in southern Utopia Planitia - a key low-latitude Martian region - have provided unprecedented insights into the aqueous process. The dataset yields vital constraints for modeling Mars' hydrological evolution from the Hesperian to Amazonian periods. Crucially, these findings will support in guiding the landing site prioritization for China's Tianwen-3 sample return mission, with the expectation of making significant discoveries in the study of habitability on Mars.

References: 

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