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Mars: liquid water stayed longer than expected – there may have been groundwater near the surface as late as the modern era of Mars

Late Water: Mars may have had liquid water for much longer than previously thought. The Chinese Mars probe Zhurong discovered evidence of this during analyzes of rocks in the Martian plain Utopia Planitia. There he identified mineral crusts of hydrated silicate and sulfate, which must have formed from rising saline groundwater. This means that there has been liquid water under the surface of Mars at this point for the past 1.8 billion years.

Mars was much more favorable in its early days than it is today, and it had lakes, rivers, and perhaps even an ocean. So far, however, there has been a disagreement how much Liquid water already exists on the red planet and how long does it last. According to current assumptions, there was already a climate change about 3.5 billion years ago No permanent repetitions Liquid water is more on Mars. By the beginning of the Amazon period about 1.8 billion years ago, the temporary water sources would have finally dried up.

The landing site of the Zhurong rover in the southern Utopia Planitia plain. © NASA/JPL

or not? According to some hypotheses, even in the cold, dry modern era of Mars, water from hydrothermal vents or other heated groundwater sources could have appeared at the surface at least occasionally. Evidence for this includes riverbeds that cut through the smaller layers of rock.

Two different types of rocks

China’s Mars rover Zhurong can now find additional indications of such “late” water. Born in May 2021 by Mars mission Tianwen-1 Scattered to the south of the plain of Utopia Planitia – the largest impact basin on the Red Planet. During the 92 days of its mission to Mars, the rover used six scientific instruments to study morphology, mineralogy, surface structure and ice distribution around its landing site. Yang Liu of the National Aerospace Research Center in Beijing and colleagues analyzed this data.

Accordingly, there are two different types of rocks at the rover landing site. The first includes dark basalt rocks believed to be of older and deeper layers. On the other hand, the second type of rock is light in color, and some of the darker pieces have a light coating as well. The light-colored crust is often scaly and scaly and, according to studies, dates back to the Amazonian period – and therefore is younger than 1.8 billion years.

hydrated silicate and sulfate peels

But crucially, spectroscopy of the light-colored rocks revealed that they contain hydrated minerals—minerals that have water bound in their structure and typically form on Earth in the presence of liquid water. According to Liu and colleagues, the spectral fingerprints of the Martian rocks can match those of hydrated silicates and sulfates, as well as gypsum.

Looking at the layers of light that partially formed around the dark cores, they assume that it is a kind of hard crust – hard crusts formed by the deposition of minerals from the porous waters of rocks. In the case of Mars’ crusts, researchers believe they formed when brine rose underground during phases of rising groundwater levels. Then the salty mineral crusts formed as evaporation from the near surface increased the salinity of this porous water.

crust formation
A possible scenario for the formation of aqueous crusts on Mars. © Liu et al / Science Advances, CC by nc 4.0

Volcanoes or warm climates

According to scientists, Martian mineral crusts indicate that shallow groundwater existed as late as the Amazonian period. This elevation has risen high enough, at least temporarily, to absorb the regolith and lead to the formation of durable crusts. “These observations indicate that water activity on Mars has persisted for much longer than previously thought,” Liu and his team wrote.

They see warming from volcanic activity as possible reasons for this late presence of liquid water, but also temporary warm phases of the climate due to the oscillation of Mars’ axis. Over the course of Mars’ history, this has repeatedly changed its direction by more than a dozen degrees, and thus also affected the regional solar radiation. During one of these interglacial periods, southern Utopia Planitia and other areas may have experienced at least intermittent temperatures as saline groundwater remains liquid.

Water for future Mars astronauts?

However, the new findings also have potential implications for future Mars missions: “The Zhurong landing site and other areas of the Northern Plains may contain large amounts of usable water in the form of wet minerals and subsurface ice, which will be used by future Mars exploration. As a pro-resource location,” the research team confirms. (Advances of Science, 2022; doi: 10.1126/sciadv.abn8555)

Source: American Association for the Advancement of Science (AAAS)