Billions of years ago, Mars was a very different world compared to the frigid desert it is today. It had water on its surface. The moment that disappeared into the air or underground has not been well established, and recent research suggests that it may have actually been wet for longer than previously thought. Now, the Chinese Zhurong Mars rover has found more evidence supporting this scenario.
The six-wheeled robot is exploring Utopia Planitia, Mars’s largest impact basin (also the largest in the Solar System) at 3,300 kilometers across. It was last visited in the 1970s by NASA’s Viking 2 before Zhurong arrived. The newer robotic explorer has found rocks that appear to have formed in the presence of water, report scientists in Science Advances. This is not something unseen on Mars, but the timing of their formation is certainly exciting.
The region belongs to the Amazonian period, the extensive and more modern period of geological history on Mars. Based on statistical counts of impact on the surface, the region could have been resurfaced as late as 700 million years ago. Without direct analysis, it is difficult to estimate the actual age of the rocks, so they might be considerably older than that, but the findings still suggest that Mars had liquid water and ice on its surface for a long while.
The team also found that the area Zhurong has been exploring is made of a hard layer of soil or duricrust that has different characteristics compared to what has been seen in other locations – like that which caused the “death” of the Mole experiment, part of NASA's InSight mission. The team believes that the particular duricrust – a hard layer on or near the surface of the soil – could have formed through the presence of briny groundwater, slowly evaporating, cementing the duricrust.
The presence of liquid water underground in the recent geological past has implications for our understanding of Mars, the possibility of life there in the past or even today, and any future exploration – whether robotic or in person.
“The in situ identification of such environments points to a more active Amazonian surface hydrosphere for Mars than previously considered. 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 authors wrote in the paper.
Mars continues to hold the secrets of its water-rich past close to its chest, but slowly and surely we are getting better at discovering them.