(CN) — Scientists have long thought that Mars was once wet and inhabitable. But until recently, they'd assumed the last drops evaporated around 3 billion years ago. Now, new evidence is emerging that the water lasted much longer: Caltech researchers have identified salt deposits in images captured by NASA's Mars Reconnaissance Orbiter, suggesting that liquid water was present on the surface of the Red Planet recently as 2 billion years ago.
And according to a new paper by a team of Chinese scientists, published Wednesday in Science Advances, Mars' last few billion years, known as the Amazonian epoch, may have been even wetter than we once thought.
China's Zhurong rover touched down in the southern part of Mars' Utopia basin in May 2021. Professor Yang Liu of the National Space Science Center in Beijing and his team used short-wave infrared spectral data collected by the Zhurong rover to identify "hydrated sulfate/silica materials," evidence of "substantial liquid water" which came from either "groundwater rising or subsurface ice melting."
Liu and his team also found evidence of an abundance of ground ice near where the Zhurong rover landed.
"The Zhurong landing site (and the northern lowlands) may contain a considerable amount of accessible water in the form of hydrated minerals and possibly ground ice for in situ resource utilization for future human Mars exploration," the study authors wrote.
In other words, there might be a lot of ice underneath the surface of Mars, and we might know where it is, and humans could, in theory, use it to aid in manned exploration of the planet.
In another paper, also published Wednesday in Science Advances, a team of European researchers analyzed a nakhlite meteorite — a rock from Mars that somehow made it to Earth — and found the rock was altered by water while still on Mars during the Amazonian epoch.
The team led by Josefin Martell, a doctoral student at Lund University in Sweden, used nondestructive imaging technology to study the meteorite, which is believed to have been dislodged from Mars by a volcanic explosion and crashed into Earth sometime in the last 10,000 years. Data they gathered implies the liquid water "was localized and originated from the melting of local subsurface ice following an impact event," the study authors wrote.
From this, they infer that "the Martian crust sampled by the nakhlites could not have provided habitable environments that could harbor any life on Mars during the Amazonian."
"Our results have direct implications for the habitability of the Martian subsurface in the nakhlite source region, where any habitable environments were localized and very short-lived, reducing the chance of life’s emergence or survival on Mars during the Amazonian period," they write.
In other words, there probably weren't any Martians on Mars in the last two or three billion years.
Wednesday's study marks an early usage of neutron and X-ray tomography, which may prove to be a valuable tool for studying the geology of other planets in order to discover evidence of the historical existence of water.
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