Billions of years ago, Mars rippled with rivers, ponds and an ocean that could have covered about 20 percent of the red planet. But the nice wet environment on Mars did not last and it started losing its atmosphere over the course of time. When the atmosphere became too thin, two-thirds of its ancient ocean evaporated to space and about one-third remains still in the form of the Martian polar ice caps. But when did Mars lose its last drop of liquid water? While scientists previously thought that it happened some three billion years ago. Now, a new study by scientists at the California Institute of Technology, published on the Caltech website, has found that liquid water flowed on Mars as late as two billion years ago.
Using data from NASA’s Mars Reconnaissance Orbiter, scientists found chloride salt deposits on the top of volcanic terrain that formed about 2.3 billion years ago. Scientists also analysed various salt deposits across different types of landforms across the red planet. Scientists found that salt deposits were surprisingly thin, less than even three metres, and were found in low-lying regions.
They also found that such salt deposits were in shallow depressions, sometimes perched above big craters, indicating that the water came there flowing from the surface, froze, cracked them, and melted in a cycle called a freeze-thaw cycle. This caused the chloride salt deposits to leach in those depressions. Many of such deposits were found atop terrains that formed about 2.3 billion years ago, which means the freeze-thaw cycle of water happened after that, indicating that liquid water existed even after those terrains were formed.
The new timeline means water on Mars stayed for much longer than previously thought. Data from the Curiosity Mars rover had shown back in 2015 that Mars was wet for one-and-a-half billion years. The new timelines extend Mars' wet period by almost a billion years. Notably, this is a far longer period than it took life to emerge on wet Earth. So does this mean Mars had life too? Perseverance and other Mars probes are looking for answers to that very question.
“This offers us new targets for future missions to Mars,” says Ellen Leask, the lead author of the study, in a statement. The study was published on December 27, 2021, in AGU Advances.