Much of Mars seems like an endless expanse of alien desert, with no river or lake in sight. However, liquid water definitely existed in the distant past of the planet. The new article also suggests that small amounts of water may still exist in what would otherwise appear as streaks.
Before China’s Zhurong (also known as Phoenix) rover went into hibernation last May, researchers from the National Astronomical Observatory and the Institute of Atmospheric Physics of the Chinese Academy of Sciences discovered something unexpected. Zhurong explored the Utopia Plains region, which is located near the planet’s equator. It was believed that liquid water does not exist at these latitudes. However, when the rover returned data from its Multispectral Camera (MSCam), Navigation and Terrain Camera (NaTeCam), and Martian Surface Composition Detector (MarSCoDe), possible evidence for the existence of liquid water less than half a million years ago emerged.
“[Our findings] suggest [features] associated with the activity of salt water, which indicates the existence of a water process in the low-latitude region of Mars, ”the researchers said in a study recently published in Science Advances.
Dry with a raw past
Zhurong is part of China’s Tianwen-1 Martian mission, which has helped expand our understanding of the environment on Mars. But the evidence that liquid water existed recently (at least from a geological point of view) is unexpected. Because Mars has lost most of its atmosphere and is exposed to intense radiation and the solar wind, it was previously thought that water could not exist there as a liquid. Whatever is formed must quickly freeze or evaporate due to the extremely low pressure and lack of water vapor.
It is especially dry at lower latitudes where there are no glaciers, but Zhurong found features on the surface of the dunes that aroused the suspicion of researchers led by geologist Xiaoguang Qin. These include cracks and crusts that must have been left by the evaporation of liquid water from the reddish soil. Further investigation revealed that the surfaces of these dunes were hiding hydrated silica and sulfates, minerals containing water molecules, along with some iron oxides and something like chlorides.
Both the presence of these substances and the surface features observed by Zhurong most likely indicate that frost or snow once fell, melted and seeped into the topsoil. It formed a brine after interacting with the salt in the dunes and formed something like cement when combined with grains of sand. These cements turn into crusts after evaporation.
How did it get here?
But if there really was water at lower latitudes no more than 1.4 million and only 400,000 years ago, then how did it get there?
Mars has gone through different eras, just like the Earth. Its Amazonian period began about 2.9 billion years ago and continues to the present. After the transition from the Hesperian to the Amazonian period, Mars was no longer bombarded by asteroids, and volcanic activity (some of which was caused by these collisions) decreased significantly. Although much of its atmosphere had disappeared by then and the climate was drying up, there were still warm and humid periods.
Qin and his team believe that it was during these periods that water vapor from the frozen poles spread to the warmer equator. This vapor solidifies into snow or frost in cooler weather and falls to the ground. It then melted and evaporated as the temperature rose, leaving a salty crust.
This discovery may have implications for past or present habitability on Mars. As the climate changed, so did the planet’s potential for life (although it remains a mystery whether it ever existed). Future rovers may be looking for signs of life in areas previously ignored, especially where there are crusts, cracks and depressions that could be clear signs of the presence of water.
“Because salt water once existed at different latitudes on the surface of Mars,” the researchers say, “future missions to search for existing life on Mars should prioritize salt-tolerant microbes.”
Scientific achievements, 2023. DOI: 10.1126/sciadv.add886 (About DOI).
Elizabeth Rein is a creature that writes. Her work has appeared on SYFY WIRE, Space.com, Live Science, Grunge, Den of Geek and Forbidden Futures. When she’s not writing, she’s either shape-shifting or painting or cosplaying a character no one has ever heard of. Follow her on Twitter @quothravenrayne.