Mars: a large part of his water would still be buried underground

Several billion years ago, liquid water shaped the landscape of Mars, sheltered by a beautiful atmosphere.All this water has since disappeared from the surface.The question is: where did it go?According to researchers from JPL and Caltech, a large part probably hides underground.

About four billion years ago, Mars looked very much like the earth.Studies suggest that the planet housed an ocean in its northern hemisphere, which at the time contained as much water as half of the Atlantic.But make a quick "a billion year advance and you only find a cold and incredibly dry desert.From this wet past, there are only scars today that our rivers and orbiters are responsible for studying.

So where did all this water go?The generally accepted answer is that it has escaped in space.

No magnetic field, no liquid water

Compared to the earth, Mars is not very massive, which means that its gravitational field is quite low.Consequently, the diazote present in its primitive atmosphere has escaped fairly quickly.The planet also quickly cooled, which had the effect of solidifying its formerly liquid nucleus.And without liquid nucleus, no magnetic field.

Then follows a chain reaction.Deprived of its magnetic field, Mars ended up at the mercy of the solar wind which eroded its atmosphere.The volcanism of the planet having also decreased, its atmosphere therefore had more and more difficult to renew itself.In fact, atmospheric pressure has decreased, and we know that the lower the pressure, the more the liquid state has trouble maintaining itself.

Little by little, Martian water then turned into steam, before finally escaping into space.

That said, if part of Martian water has certainly escaped this way, a team of researchers maintains that this process cannot explain the entire loss.According to their calculations, a large part of this water is integrated into the minerals of the earthly crust.

At least 30 % of the original water still there

As part of this work, the authors examined the amount of water in all its forms lining the Martian landscape during its history.They also took into account the chemical composition of its atmosphere and its crust.

The team then focused on the "light" hydrogen ratio with "heavy" (or deuterium) hydrogen (or Deuterium).Deuterium is a rare and heavier hydrogen isotope with an additional neutron in its nucleus.In fact, it is less likely to be lost in space than the lighter shape.

This means that over time, if the water vapor escaped in space, it would leave behind a higher ratio of Deuterium compared to ordinary hydrogen in the atmosphere.

However, after examining this report, they realized that something did not stick.Given the amount of water that the planet was supposed to contain, and taking into account the hydrogen leakage rate observed by spacecraft, the current deuterium/hydrogen ratio cannot be explained by atmospheric loss alone.Instead, they suggest that a large part - from 30 to 99 % - has infiltrated the minerals of the ground.

"Whenever you have a rock and interact with water, there is a series of very complex reactions which form a hydrated mineral," explains Eva Scheller, who co-signs these works.This process, called "chemical alteration", also takes place on earth (clay is an example).

On Earth, this absorbed water is then recycled in the atmosphere by the play of plates and volcanism tectonics.But Mars is not subject to these geological whims.Also, if water has effectively found trapped in the ground, it is probably still there.

The details of the study are published in the journal Science.