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An image taken by the Curiosity Rover MastCam instrument shows layers of sedimentary rock making up Mount Sharp. The rover drove from the bottom of Gale Crater through the rocks of these hills in order to understand how the rocks go from the bottom in the (oldest) section to the highest in the (younger) section. The rover has crossed rocks over 400 meters above sea level since the start of the mission. Credit: NASA’s Mars Curiosity Rover
In 2012, Nasa landed the Curiosity rover in Gale crater on March because the crater was believed by many scientists to be the site of an ancient lake on Mars over 3 billion years ago. Since then, the rover has been driving performing geological analyzes with its suite of instruments for more than 3,190 sols (Martian days, equivalent to 3,278 Earth days). After analyzing the data, researchers from the Department of Earth Sciences at the University of Hong Kong’s (HKU) Faculty of Science proposed that the sediment measured by the rover during most of the mission did not actually formed in a lake.
The team of researchers suggested that the large mound of sedimentary rock explored and analyzed over the past eight years actually represents sand and silt deposited as air drops from the atmosphere and disturbed by the wind. The weathering minerals formed by the interaction between water and sand did not occur in a lake environment. The “wet” environment, they suggest, actually represents an alteration similar to the formation of soil under rain in an ancient atmosphere that was very different from the present.
These images show Gale Crater in high-resolution stereo camera (HRSC) images, with elevation colorized in blue. The image on the left shows the Standard Model where Gale Crater is generally assumed to have been a large lake (flooded to at least an elevation of around 4000m). The image on the right is the model proposed by Liu et al., In which only very small, shallow lakes existed at the bottom of Gale Crater (the crater being inundated only at an altitude of about 4,500 m). Most of the sediment was deposited from the atmosphere as airfall deposits and later altered by precipitation or melting ice. A star marks the rover’s landing site. Credit: ESA / HRSC / DLR
The discovery was recently published in Scientists progress in an article edited by postgraduate research student Jiacheng LIU, his advisor, Associate Professor Dr Joe MICHALSKI, and co-author Professor Mei Fu ZHOU, all affiliated with the Department of Earth Sciences. The researchers used chemical measurements and X-ray diffraction (XRD) measurements, in addition to rock texture images, to reveal how rock composition trends relate to geological processes.
“Jiacheng has demonstrated very important chemical patterns in rocks, which cannot be explained in the context of a lake environment,” said Dr. Michalski. “The key point is that some elements are mobile, or easy to dissolve in water, and some elements are immobile, or in other words, they stay in rocks. Whether an element is mobile or stationary depends not only on the type of element but also on the properties of the fluid. Was the fluid acidic, saline, oxidizing, etc. Jiacheng’s results show that stationary elements are correlated with each other and highly enriched at higher elevations in the rock profile. This indicates top-down weathering as you see in soils. In addition, it shows that iron is depleted as weathering increases, meaning that the atmosphere at the time was shrinking on ancient Mars, and not oxidizing like it is on today’s rusty planet.
Understanding how the Martian atmosphere and the surface environment as a whole evolved is important for the exploration of possible life on Mars, as well as for our understanding of how the Earth may have changed early in its history. . “Obviously, studying Mars is extremely difficult and the integration of creative and technologically advanced methodologies is necessary. Liu and his co-authors made intriguing observations through the use of remote sensing techniques to understand the chemical composition of ancient sediments that inform their early development. Their data challenge existing hypotheses for both the deposition environment of these unique rock formations and the atmospheric conditions in which they formed – in particular, the authors show evidence of weathering processes under a reducing atmosphere. in a subareal desert-like environment, rather than formation in a watery lake environment. Indeed, this work will inspire new and exciting directions for future research. Department of Earth Sciences assistant professor Dr Ryan McKenzie added.
China successfully landed its first lander, Zhurong, on Mars in May this year. Zhurong is currently roaming the plains of Utopia Planitia, exploring mineralogical and chemical clues of recent climate change. China is also planning a sample return mission that may take place at the end of this decade.
About the HKU Research Team:
The Department of Earth Sciences, the Research Division for Earth and Planetary Sciences and the Space Research Laboratory specialize in the application of traditional techniques and skills in Earth and environmental sciences. to the challenges of modern space science. Dr Joe Michalski heads the Planetary Spectroscopy and Mineralogy Laboratory at HKU and is the Deputy Director of the Space Research Laboratory.
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