The Zhurong Rover found evidence of water at low latitudes in modern times

The Zhurong rover has found evidence of water on the surface of dunes on modern Mars by providing primary observational evidence of liquid water at low Martian latitudes, according to a study led by Prof. QIN Xiaoguang of the Institute of Geology and Geophysics (IGG) in China. Academy of Sciences (CAS).

The study was published in Science Advances on April 28th.

Researchers from the National Astronomical Observatories of CAS and the Institute of Atmospheric Physics of CAS were also involved in the research.

Previous studies have provided evidence of large amounts of liquid water on early Mars, but with the loss of the early Martian atmosphere during a later period, the climate changed dramatically. The extremely low pressure and water vapor content make it difficult for liquid water to exist sustainably on Mars today. Hence, it is widely believed that water can only exist there in a solid or gaseous form.

Nonetheless, the drops observed on the Phoenix robotic arm prove that salty liquid water can appear in summer at the current high latitudes on Mars. Numerical simulations also show that climatic conditions suitable for liquid water could briefly exist in certain regions of Mars today. But until now, there has been no evidence to suggest liquid water at low latitudes on Mars.

Now, however, finds from the Zhurong explorer filled in the gaps. 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 on the southern edge of the Planitia Utopia Plain (UP) (109.925 E, 25.066 N) , where the northern lowland unit is at.

The researchers used data obtained by the Navigation and Terrain Camera (NaTeCam), the Multispectral Camera (MSCam), and the Mars Surface Composition Detector (MarSCoDe) aboard the Zhurong rover to study surface features of different scales and the composition of dune material in the landing area.

They found several important morphological features on the surface of the dunes, such as scaling, fissures, granulations, polygonal ridges and strip-like tracks. Analysis of the spectral data revealed that the dune surface layer is rich in hydrated sulfates, hydrated silica (mainly opal-CT), trivalent iron oxide minerals (mainly ferrihydrite), and possibly chlorides.

“According to meteorological data measured by Zhurong and other Mars rovers, we conclude that the surface characteristics of these dunes are related to the involvement of molten brines formed by the subsequent melting of ice/snow that falls on the surface of the saline dunes during cooling. ,” said Prof. QIN.

Specifically, the salt in the dunes causes the frost/snow to melt at low temperatures to form salty liquid water. When the brine dries, precipitated hydrated sulfate, opal, iron oxide, and other hydrated mineral cement sand particles to form sand aggregates and even crust. Then the crust cracks even more due to shrinkage. The subsequent melting of ice/snow forms polygonal ridges and strip-like tracks on the surface of the crust.

Estimates of the ages of the dunes (approximately 0.4–1.4 million years) and the relationship between the three water phases suggest that the transfer of water vapor from the polar ice sheets towards the equator during the large oblique stage of the late Martian Amazon period led to a recurrent humid environment at low latitudes. Therefore, a water activity scenario has been proposed, namely, cooling at low latitudes during the major tilt stage of Mars promotes frost/snow fall and subsequently results in the formation of crusts and aggregates on the surface of the salty dunes, thereby strengthening the dunes and leaving traces. liquid brine activity.

This discovery provides the main observational evidence of liquid water at low latitudes on Mars, 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 habitable environments, and providing key clues for the search for future life,” said Prof. QIN.