Billions of years ago, Mars had plenty of water, and even featured rivers and oceans. However, all of that water was lost and even today, the planet leaks hydrogen into space.

Scientists have reportedly identified a water-cycle that might explain how Mars became so “dehydrated”, while Earth managed to retain its reserves.

Mars has a middle atmospheric layer, like Earth, that should restrain rising gas, causing it to turn to ice and drop back to the planet surface.

Scientists used computer simulations to discover a previously unknown mechanism that punctures that protective layer.

Billions of years ago, #Mars was a planet rich in water with rivers, and even an ocean. https://t.co/1IsCQCQAZb — cosmic database (@cosmicdatabase) May 10, 2019

Every two Earth years, summertime hits the southern hemisphere of Mars, when water vapor rises from the lower to the upper atmosphere. From there, winds carry most of the rare gas to the North Pole, where it sinks once again, but part of it escapes into space.

The Martian orbit of the Sun is much more elliptical than ours and when it’s summer in the southern hemisphere, the planet is closest to its star, meaning that it’s much warmer than a northern hemisphere summer.

"When it is summer in the southern hemisphere, at certain times of day water vapour can rise locally with warmer air masses and reach the upper atmosphere," said Dr. Paul Hartogh from the Moscow Institute of Physics and Technology (MPS) in a statement.

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Another problem is the vast dust storms that span the entire planet and repeatedly afflict Mars at intervals of several years. The last such storms occurred in 2007 and 2018 and were documented by space probes orbiting Mars.

"The amounts of dust swirling through the atmosphere during such a storm facilitate the transport of water vapour into high layers of the air," says Alexander Medvedev from MPS.

Dust particles can absorb sunlight and heat up, elevating temperatures in the atmosphere by as much as 30 degrees.

"Our model shows with unprecedented accuracy how dust in the atmosphere affects the micro-physical processes involved in the transformation of ice into water vapour," explains Dmitry Shaposhnikov of MPS, first author of the new study, which was a collaboration between Moscow Institute of Physics and Technology and the Max Planck Institute for Solar System Research (MPS) in Germany.

The research was published in Geophysical Research Letters.

"The new seasonal water cycle that has been found contributes massively to Mars' continuing loss of water," Paul Hartogh from MPS said, summarising the results of the new study.