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New study offers clues about how Mars lost its water


Mars is known for its thin atmosphere, where CO2 dominates and provides most of the atmospheric mass and pressure. In fact, the pressure is similar to that in the Earth’s stratosphere, which is a layer of the atmosphere, at more than 30km above the surface.

But what about water? Water on Mars is currently found on the surface as a layer of ice – several kilometers thick – at the north pole. It also appears as seasonal frost at the coldest times of the year, and in the atmosphere as vapor and ice. Nevertheless, the Martian atmosphere is extremely dry compared to Earth’s, with about 100 times less water. While precipitation on Earth results in water layers several centimeters thick, water that would precipitate on Mars would only form a thin film of less than a millimeter.

New data now provides a better understanding of why there is (almost) no water left on Mars.

Water escapes from the Martian atmosphere

The evidence suggests that Mars was not always the cold, arid planet we observe today. There is plenty of evidence of water on Mars’s surface in the distant past – about four billion years ago. At that time, liquid water flowed in great streams and stagnated in the form of pools or lakes, such as in the Jezero crater explored by the Perseverance rover, in search of traces of past life.