Most of Mars appears to be an endless stretch of eerie desert, with no river or lake in sight. However, liquid water certainly existed in the planet’s distant past. A new paper also suggests that small amounts of water are also likely to be present in seemingly barren places.
Before the Zhurong (also known as Phoenix) rover went into hibernation last May, researchers from the National Astronomical Observatories and the Institute of Atmospheric Physics under the Chinese Academy of Sciences discovered something unexpected. Zhurong was exploring the Utopia Planitia region, near the planet’s equator. No liquid water was thought to exist at these latitudes. However, when the rover sent back data from the Multispectral Camera (MSCam), Navigation and Terrain Camera (NaTeCam), and Mars Surface Composition Detector (MarSCoDe), there was potential evidence that liquid water existed less than half a million years ago.
“[Our findings] Suggest [features] In a study recently published in Science Advances, the researchers said:
Dries with a wet past
Zhurong is part of China’s Tianwen-1 Mars mission, which has helped expand our understanding of the environment on Mars. But the evidence for liquid water recently (at least in geological terms) is unexpected. Since Mars has lost most of its atmosphere and was exposed to intense radiation and the solar wind, it was previously thought that water could not exist as a liquid there. Anything that forms must quickly freeze or evaporate due to the extremely low pressure and lack of water vapor.
It is particularly dry at low latitudes where there are no glaciers, but Zhurong found features on the dune surfaces that made the researchers, led by geologist Xiaoguang Qin, suspicious. These include cracks and crusts that must have been left when liquid water evaporated from the reddish soil. Further investigation revealed that the surfaces of these dunes concealed hydrated silica and sulfates, minerals that contain water molecules, along with some iron oxides and what appear to be chlorides.
The presence of these materials and the surface features noted by Zhurong most likely indicate that frost or snow once fell, melted, and seeped into the upper layer of soil. It formed brine after it interacted with the salt in the dunes, and formed something like cement when combined with grains of sand. These cements become flakes after they evaporate.
How did this get here?
But if there was indeed water at lower latitudes no more than 1.4 million and less than 400,000 years ago, how did it get there?
Mars has gone through different eras just like Earth. The Amazonian period began about 2.9 billion years ago and extends to the present. After the transition from the Hesperian to the Amazonian period, Mars is no longer surrounded by asteroids, while volcanic activity (which resulted from some of these collisions) has greatly decreased. Although by then most of the atmosphere had disappeared, and the climate was drying up, there were still warm and wet periods.
Chen and his team believe that during these periods water vapor diffused from the frigid poles to the warmer equator. This vapor will freeze into snow or sleet during cold weather and fall to the ground. Then it melts and evaporates when temperatures rise, leaving behind salty crusts.
This discovery could have implications for the past or present habitability of Mars. As the climate has evolved, so has the planet’s potential to host life (although whether it ever happened remains a mystery). Future rovers may look for signs of life in previously overlooked areas, especially where there are crusts, cracks, and depressions that might have been signs of water previously.
“Because salt water was previously present at different latitudes on Mars, salt-tolerant microbes should be prioritized in future missions looking for surviving life on Mars,” the researchers said.
Science Advances, 2023. DOI: 10.1126/sciadv.add886.001 (about DOIs).
Elizabeth Raine Creature Writes. Her work has appeared on SYFY WIRE, Space.com, Live Science, Grunge, Den of Geek, and Forbidden Futures. When not writing, she either changes shape, draws, or disguises herself as a character no one has ever heard of. Follow her on Twitter: @hravenrayne.
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