“Late” water on Mars

So far, it is unclear how long Mars lived and how long liquid water existed. The Zhurong Chinese Mars Rover now provides exciting data in this regard. Because his analyzes of rock samples to the south of the major shock depression Utopia Planitia suggest that there was water at or just below the surface during the most recent age of the planet. Scientists see evidence of this hydrated silicates and sulfates that must have arisen in the Amazon Era, which began about 1.8 billion years ago. In their opinion, this may indicate that liquid water has existed, at least occasionally, on the Red Planet longer than previously thought.

Our neighbor planet Mars was probably warmer and more bearable in its early days than it is today. At that time, it was widely assumed that it had a denser atmosphere, lakes, rivers, and, according to some researchers, maybe even the ocean. So far, however, it is disputed how much liquid water actually existed at that time, and how long it remained. As the Red Planet’s climate changed after a milder early period, it lost much of its atmosphere and became colder and drier. At the latest at the beginning of the Amazon period, about 1.8 billion years ago, but probably as early as the beginning of the Hesperian Martian age 3.5 billion years ago, there were no more permanent liquid water occurrences on the surface of Mars. Today, water on Mars exists only in the form of water ice, which is found, among others, in in the polar ice caps and in the remnants of underground glaciers. It is debatable whether there is still water under the surface of Mars in the form of a liquid, highly saline brine.

Rover explores the rocks at Utopia Planitia

But what about at least the momentary appearance of liquid water? According to some hypotheses, even during the cold, dry Martian era of the modern era, water from hydrothermal vents or other sources of heated groundwater could at least sporadically appear on the surface. “Recent analyzes have identified river landscapes that cross the Amazon,” explains Yang Liu of the National Space Research Center in Beijing and his colleagues. “This indicates that even the most recent era of Mars still showed water activity that shaped the surface.” , was to deliver, inter alia, the Chinese mission Mars Tianwen-1, which dropped the Zhurong rover in May 2021 south of the Utopia Planitia plain.

Equipped with six different scientific instruments, the rover spent 92 days of its mission studying the morphology, mineralogy, surface structure and ice distribution around the landing site in the largest impact basin on Mars. The data now analyzed by Liu and his team show that there are two different types of rock in this part of Utopia Planitia. The first includes dark basalt boulders that are believed to come from older, deeper layers, the team explains. On the other hand, the second type of rock is mostly light in color, with light material sometimes forming a coating on the darker interior. “These pieces are covered with dust and often show flaky or flaky surfaces that indicate physical weathering from heat and wind stress,” the researchers said. Based on research and geological conditions, they conclude that these pieces must come from the Amazon period.

Hydrated mineral crusts indicate pore water

Closer analysis of the bright rocks using various spectrometers showed that these solids contain hydrated minerals – minerals that have water bound in their structure and that are normally formed on Earth in the presence of liquid water. According to Liu and his colleagues, the spectral signatures of Martian rocks may correspond to those of hydrated silicates and sulphates, as well as gypsum. Given the light layers partially formed around dark nuclei, they hypothesize that it is a kind of hard shell – a hard shell formed by the precipitation of minerals from the rock pore water. In the case of the Martian crust, scientists suspect that they formed when the brine rose underground in phases of higher groundwater levels. Mineral salt crusts then formed, where evaporation from the nearby surface further increased the salinity of this pore water.

According to scientists, the existence of these mineral crusts suggests that in the Amazon period there was still enough groundwater to temporarily saturate the subsurface subsoil and lead to the formation of a duric crust. “These observations suggest that water activity on Mars lasted much longer than previously thought,” writes Liu and his team. They see volcanic activity and vibrations on the Martian axis as possible causes of the episodic occurrence of liquid water underground. Since this has changed many times over a dozen degrees throughout the history of Mars, a slightly milder climate may have existed in southern Utopia Planitia and other areas, at least temporarily.

However, the new results also have potential implications for future manned missions to Mars: “The Zhurong landing site and other areas of the northern plains may contain significant amounts of usable water in the form of hydrated minerals and subsurface ice that will be used in future Mars exploration as a pro-resource. . -local “- emphasizes the research team.

Source: Yang Liu (National Space Science Center, Chinese Academy of Sciences, Beijing) et al., Science Advances, doi: 10.1126 / sciadv.abn8555

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