Late Water: Mars may have had liquid water longer than previously thought. The Chinese Mars rover Zhurong discovered evidence of this during rock analyzes in the Mars plain Utopia Planitia. There he identified mineral crusts of hydrated silicates and sulfates, which must have been formed by rising, saline groundwater. This means that there has been liquid water in the subsurface of Mars at this point for the last 1.8 billion years.
Mars was more habitable in its early days than it is today, and had lakes, rivers, and maybe even an ocean. So far, however, it has been disputed how much liquid water actually existed on the red planet and how long it lasted. According to current assumptions, there was already a climate change around 3.5 billion years ago no permanent occurrences liquid water more on the surface of Mars. With the beginning of the Amazonian period around 1.8 billion years ago, even temporary water sources might have finally dried up.
Or not? According to some hypotheses, even in the cold, dry Martian modern era, water from hydrothermal vents or other warmed groundwater sources might have surfaced at least occasionally. Evidence of this includes riverbeds that cut through younger layers of rock.
Two different rock types
The Chinese Mars rover Zhurong might now have found further indications of such a “late” water. He was born in May 2021 by the Tianwen-1-Marsmission Deployed to the south of the Utopia Planitia plain – the Red Planet’s largest impact sink. During the 92 days of its Martian mission, the rover used six scientific instruments to study the morphology, mineralogy, surface structure and ice distribution around its landing site. Yang Liu from the National Space Research Center in Beijing and his colleagues analyzed this data.
Accordingly, there are two different types of rock at the landing site of the rover. The first includes dark basaltic boulders believed to be from older, deeper strata. The second type of rock, on the other hand, is light in color, and some darker chunks also have a light coating. The light-colored crust is also often scaly and flaky and, according to the studies, dates back to the Amazonian period – it is therefore younger than 1.8 billion years.
Crusts of hydrated silicates and sulfates
Crucially, however, spectroscopic analysis of the light-colored rock revealed that it contains hydrated minerals — minerals that have water bound in their structure and are normally formed on Earth in the presence of liquid water. The spectral signatures of Martian rocks might match those of hydrated silicates and sulfates, as well as gypsum, according to Liu and his colleagues.
Given the light layers partially formed around dark cores, they hypothesize that it is a type of duric crust — hard crusts formed by the precipitation of minerals from the pore water of rocks. In the case of the Martian crusts, the researchers suspect that they formed when saline brine rose underground during phases of higher groundwater levels. The saline mineral crusts then formed where evaporation from the nearby surface further increased the salinity of this pore water.
Volcanoes or climatic warm phases
According to the scientists, the Martian mineral crusts suggest that shallow groundwater existed as late as the Amazonian period. This rose, at least temporarily, high enough to wet the regolith and lead to the formation of the duric crusts. “These observations suggest that aqueous activity on Mars has lasted far longer than previously thought,” Liu and his team write.
They see warming due to volcanic activity as possible causes for this late occurrence of liquid water, but also temporary warm phases of the climate due to the swinging of the Martian axis. In the course of Martian history, this has repeatedly changed its orientation by more than a dozen degrees and thus also influenced the regional solar radiation. During one of these interglacial periods, southern Utopia Planitia and other areas may have experienced at least intermittent temperatures at which saline groundwater remains liquid.
Water for future Mars astronauts?
However, the new results also have potential implications for future manned Mars missions: “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, which future Mars exploration will use as a pro… -place resource,” emphasizes the research team. (Science Advances, 2022; doi: 10.1126/sciadv.abn8555)
Quelle: American Association for the Advancement of Science (AAAS)
