China’s Zhurong rover has found evidence for water on dune surfaces of modern Mars, providing key observational evidence of liquid water at low Martian latitudes. Previous studies have provided evidence of a large amount of liquid water on early Mars, but with the escape of the early Martian atmosphere during the last period, the climate changed dramatically.
The very low pressure and water vapor content make it difficult for liquid water to sustainably exist on Mars today; therefore, it has been widely believed that water can only exist there in a solid or gaseous form.
However, the droplets observed on the Phoenix robotic arm prove that salty liquid water can appear in the summer at today’s high latitudes on Mars. Numerical simulations have also shown that weather conditions suitable for liquid water may briefly occur in certain areas of Mars today.
However, until now, no evidence has shown the presence of liquid water at low latitudes on Mars. Now, the findings from the Zhurong rover fill the gap. The said rover, which is part of China’s Tianwen-1 Mars exploration mission, successfully landed on Mars on May 15, 2021. The landing site is at the southern end of the Utopia Planitia (UP) plain (109.925 E , 25,066 N), where the northern lowland unit is located.
How did they do it?
The Chinese researchers, led by Professor Qin Xiaoguang from the Institute of Geology and Geophysics (IGG) of China, used data obtained from the Navigation and Terrain Camera (NaTeCam), the Multispectral Camera (MSCam) and the Composition Detector of the surface of Mars (MarSCoDe) aboard the Zhurong rover to study the surface features at different scales and the material compositions of the dunes in the landing area.
They found some important morphological features on the dune surfaces, such as crusts, cracks, granulation, polygonal ridges, and a strip-like trail. Analysis of the spectral data revealed that the surface layer of the dune is rich in hydrated sulfates, hydrated silica (especially CT opal), trivalent iron oxide minerals (especially ferrihydrite), and possibly chlorides.
“Based on meteorological data measured by Zhurong and other Mars rovers, we inferred that these dune surface features were related to the involvement of liquid saline water formed by subsequent melting of frost/snow falling on the dune surfaces. dunes that contain salt when cooling occurs,” Professor Qin, whose study was published in Science Advances, said in a statement.
Specifically, the salts in the dunes cause frost/snow to melt at low temperatures to form salty liquid water. When the saline water dries, the precipitated hydrated sulfate, opal, iron oxide, and other hydrated minerals cement the sand particles to form sand aggregates and even crust. The bark then cracks further from shrinkage. The subsequent frost/snow melting process forms more polygonal ridges and a strip-like trail on the crustal surface.
The estimated age of the dunes (about 0.4 to 1.4 million years) and the relationship between the three water phases suggest that the transfer of water vapor from the polar ice cap toward the equator during the great stages obliquity of the late Amazonian period of Mars led to repeated wet environments at low latitudes. Therefore, a water activity scenario has been proposed, i.e. cooling at low latitudes during the large obliquity stages of Mars causes frost/snow fall and subsequently results in the formation of crusts and aggregates on the surface of salty dunes, solidifying the dunes and leaving traces of liquid saline water activity.
Importance
The discovery provides key observational evidence for liquid water at low Martian 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, searching for a habitable environment, and providing key clues for the future search for life,” said Professor Qin.
