This is why Mars would have lost almost all of its water until it dried up

Mars once had seas. Geological evidence indicates that the red planet may have harbored abundant water on its surface , making it a potentially habitable world some 3 billion years ago. However, over time, it transformed into an arid, dry, and hostile planet.

Now, a study published in Nature Astronomy offers a new explanation for how Mars lost almost all of its water , complementing previous theories about the disappearance of its atmosphere and lack of magnetic shielding.

The new analysis suggests that the tilt of the Martian rotation axis , which was much more variable in the past, was a determining factor in the accelerated loss of hydrogen, one of the key components of water.

According to the study, when Mars's axial tilt (obliquity) was around 35° , the hydrogen cycle would have accelerated dramatically. Simulations show that during these periods, the rate of hydrogen loss could have increased more than tenfold , reaching figures as high as 6 × 10²⁷ atoms per second . This would have facilitated its escape into space, taking the planet's water with it.

Currently, Mars has a 25° tilt , similar to Earth's, which allows for seasonality. However, in the past, its tilt was much more unstable, making it more vulnerable to solar wind and atmospheric loss .

Until now, scientists had attributed the loss of water on Mars primarily to the absence of a global magnetic field and the lack of active volcanism , two factors that on Earth help maintain a stable atmosphere.

Without a magnetic shield, solar winds "shave" the atmosphere , expelling essential gases like oxygen. And without active volcanoes to replenish these gases, the planet cannot maintain long-term atmospheric balance.

The new study does not rule out these causes, but complements them with the obliquity hypothesis, indicating that the planet's axial dynamics may have also played a crucial role in its transformation from a humid world to a frozen desert.