A selfie taken by the Zhurong rover next to its landing platform, captured using a wireless camera. Credit: Chinese National Space Administration
The Zhurong rover, part of China’s Tianwen-1[{” attribute=””>Mars mission, has found evidence of liquid water at low Martian latitudes, indicating potentially habitable environments. This discovery, contradicting previous beliefs that water could only exist in solid or gaseous states on Mars, was made by analyzing morphological features and mineral compositions of dunes in the landing area.
The Zhurong rover has found evidence of water on dune surfaces on modern Mars by providing key observational proof of liquid water at low Martian latitudes, according to a study led by Prof. Xiaoguang Qin from the Institute of Geology and Geophysics (IGG) of the Chinese Academy of Sciences (CAS).
The study was published on April 28 in the journal Science Advances.
Researchers from the National Astronomical Observatories of CAS and the Institute of Atmospheric Physics of CAS were also involved in the study.
Water traces on bright sand dunes. (a) Topographic contour map of the environs where the trace is located. The coordinate system is east-north-up (ENU) local Cartesian coordinate and the origin is that of the rover coordinate system. The background Digital Orthophoto Map (DOM) photo was taken by NaTeCam. (b) MSCam bird’s-eye-view photo showing a strip-like trace and a likely water-soaked fragmented soil block. (c) Enlarged photo showing polygonal cracks and bright polygonal ridges. (d) Enlarged photo showing circular region with the strip-like trace as a part. (e) NaTeCam 3D image of an interdune depression between two dark longitudinal dunes. (f) A cross-section of the dune along the profile of the white dash line in (e). Credit: IGGCAS
Previous studies have provided proof of a large amount of liquid water on early Mars, but with the escape of the early Martian atmosphere during the later period, the climate changed dramatically. Very low pressure and water vapor content make it difficult for liquid water to sustainably exist on Mars today. Thus, it has been widely believed that water can only exist there in solid or gaseous forms.
Nonetheless, droplets observed on the Phoenix’s robotic arm prove that salty liquid water can appear in the summer at current high latitudes on Mars. Numerical simulations have also shown that climatic conditions suitable for liquid water can briefly occur in certain areas of Mars today. Until now, though, no evidence has shown the presence of liquid water at low latitudes on Mars.
Now, however, findings from the Zhurong rover fill the gap. The Zhurong rover, which is part of China’s Tianwen-1 Mars exploration mission, successfully landed on Mars on May 15, 2021. The landing site is located at the southern edge of the Utopia Planitia (UP) Plain (109.925 E, 25.066 N), where the northern lowlands unit is located.
The researchers used data acquired by the Navigation and Terrain Camera (NaTeCam), Multispectral Camera (MSCam), and Mars Surface Composition Detector (MarSCoDe) aboard the Zhurong rover to study different-scale surface features. and material composition of the sands in the landing area.
They found several important morphological features on dune surfaces, such as crusts, cracks, granulations, polygonal ridges, and strip-like traces. Analysis of the spectral data revealed that the dune surficial layer is rich in hydrated sulfates, hydrated silica (especially opal-CT), trivalent iron oxide minerals (especially ferrihydrite), and possibly chlorides.
“According to the measured meteorological data by Zhurong and other Mars rovers, we found that the surface characteristics of this dune are related to the involvement of liquid salt water formed by the subsequent melting of frost /snow falling on the salt-containing dune surfaces when cooling occurs,” said Prof. Qin.
Specifically, salts in sands cause frost/snow to melt at low temperatures to form salty liquid water. When the salt water dries, the precipitated hydrated sulfate, opal, iron oxide, and other hydrated minerals cement the sand particles together to form sand aggregates and even the crust. Then the crust is further cracked by contraction. The subsequent melting process of frost/snow further forms polygonal ridges and a strip-like trace on the surface of the crust.
The estimated age of the sands (about 0.4–1.4 million years) and the association of the three water stages suggest that the migration of water vapor from the polar ice sheet to the equator during the great obliquity stages of the late Amazonian stage of Mars led to persistently humid environments at low latitudes. Therefore, a water activity scenario is proposed, i.e., cooling at low latitudes during large periods of obliquity of Mars induces the collapse of frost/snow and then results in the formation of crusts and aggregate on top of the salty dune, thus stabilizing the dunes and leaving traces. of liquid salt water activity.
The discovery provides important observational evidence of liquid water in Martian low latitudes, where surface temperatures are relatively warmer and more suitable for life than at high latitudes.
“This is important for understanding the evolutionary history of the Martian climate, finding habitable environments, and providing key clues for the future search for life,” said Prof. Qin.
Reference: “Modern water at low latitude on Mars: Potential evidence from dune surfaces” by Xiaoguang Qin, Xin Ren, Xu Wang, Jianjun Liu, Haibin Wu, Xingguo Zeng, Yong Sun, Zhaopeng Chen, Shihao Zhang, Yizhong Zhang, Wangli Chen , Bin Liu, Dawei Liu, Lin Guo, Kangkang Li, Xiangzhao Zeng, Hai Huang, Qing Zhang, Songzheng Yu, Chunlai Li and Zhengtang Guo, 28 April 2023, Advances in Science.
DOI: 10.1126/sciadv.add8868
