China’s Zhurong Mars rover has discovered evidence that liquid water flowed on the red planet within the past 1.4 million years, suggesting that modern Mars might not be as inhospitably dry as previously assumed. Given that water is the essential ingredient for life on Earth, the new findings have major implications in the ongoing search for aliens on Mars.
More than three billion years ago, Mars was home to gushing rivers and enormous lakes that might have provided the right conditions to support simple forms of life, such as microbes. But the planet has lost most of its atmosphere since that golden age, transforming it into a desiccated husk with a surface exposed to highly damaging radiation.
NASA’s rover Curiosity has proved that Mars was once habitable, and its successor, Perseverance, is currently looking for soil samples that might preserve fossilized signs of Martian life. While those missions have produced revelations about Mars’ deep past, Zhurong has now revealed that the planet may have experienced damp spells in its recent history.
Since its landing in 2021, Zhurong has traveled just over one mile through a Martian region called Utopia Planitia, though it has been inactive for almost a year after it was placed in hibernation to protect it from wintery conditions and a large sandstorm.
While it’s not clear if the rover will ever wake up, its tantalizing images reveal features on Martian dunes that “were most likely associated with the activity of saline water, indicating the existence of water process on the low-latitude region of Mars” that may have occurred as recently as 400,000 years go,” reports a study published on Friday in Science Advances.
“Does liquid water recently exist on the contemporary surface of Mars? This question is critical for understanding the recent climatic evolution of the polar ice caps, the habitable environment, and even the potential for life on Mars,” according to the study, which was led by Xiaoguang Qin, a professor at the Institute of Geology and Geophysics (IGG) of the Chinese Academy of Sciences (CAS).
“We report crusts, cracks, aggregates, and bright polygonal ridges on the surfaces of hydrated salt-rich dunes of southern Utopia Planitia (~25°N) from in situ exploration by the Zhurong rover,” the team announced. “Wind and CO2 frost processes can be ruled out as potential mechanisms. Instead, involvement of saline water from thawed frost/snow is the most likely cause.”
NASA’s now-defunct Phoenix lander detected water vapor from its perch in Mars’ north polar region, but evidence of water at lower latitudes have remained out of reach until now. During its journey across the Martian surface, Zhurong captured observations with its Navigation and Terrain Camera (NaTeCam), Multispectral Camera (MSCam), and Mars Surface Composition Detector (MarSCoDe) that helped bring the surrounding dunes into focus.
The data exposed chemicals in the dunes that are commonly produced by interactions with saltwater. Geological features in the terrain, like cracks and ridges, also appeared to have been shaped by the flow of water in the recent past, though the researchers cautioned that Zhurong’s images have limited resolution and that “other unexpected processes” could be responsible for some of the findings, according to the study.
Where did this speculative water come from? Qin and his colleagues think it may have originated in Mars’ polar latitudes. Like Earth, Mars rotates on a tilted axis, causing its poles to periodically tip closer and farther from the Sun on a 124,000-year cycle. As the poles warm during humid eras, water vapor may drift toward the equator and fall as snow on regions closer to the equator.
The team think this polar frost briefly melted into saltwater on the ground at low latitudes, creating the chemical signatures and geological formations observed by Zhurong. This mechanism is particularly intriguing because it implies that large swaths of Mars get wet on a regular basis. While most efforts to find life on Mars focus on ancient fossils, the new study raises the possibility that extremophile organisms might still exist on Mars.
“If our water hypothesis is true, then the amount of water required to form crusts on dune surfaces and leave a trace of saline water is substantially higher than what has been discussed in terms of transient liquid water (i.e., thin films of water) in previous studies,” the researchers noted.
“Our findings provide useful clues for designing future exploration strategies for Mars rovers,” the team concluded. “As saline water once existed at various latitudes on the surface of Mars, priority should be given to salt-tolerant microbes in future missions searching for extant life on Mars.”