a wet planet long before Earth

Today there is no longer any doubt that the Martian landscape was, in the distant past, shaped by the presence of liquid water. Traces of ancient rivers feeding ancient lakes are clearly visible from orbit. In addition, the Curiosity and Perseverance rovers have provided irrefutable proof of this, thanks to rock analysis and precise photographs of the sedimentary units typical of lakes. Today however, liquid water has completely disappeared from the planet’s surface.

In this great environmental change that occurred about 3 billion years ago, the Martian atmosphere played a crucial role.

A primitive atmosphere rich in water vapor.

The analysis of the atmosphere shows us that currently the Red Planet is unable to maintain liquid water on its surface. But flow traces and lake sediments tell us that the situation was drastically different more than 3 billion years ago. However, it is difficult to define what the atmospheric conditions were at that distant time.

Currently, the Martian atmosphere is very thin.  © Nasa, Wikimedia Commons, Public Domain

Currently, the Martian atmosphere is very thin. © Nasa, Wikimedia Commons, Public Domain

Therefore, scientists have set out to produce the first numerical model that traces the evolution of the Martian atmosphere from the formation of the planet to the establishment of the first oceans and lakes.

This model suggests that, like Earth, the Martian atmosphere was originally rich in water vapor, concentrated in clouds in the lower layers of the atmosphere. The upper, outermost parts would have been much drier. In contrast, dihydrogen molecules (Htwo), too light to be held, would have quickly escaped into space.

A dense atmosphere rich in Htwo allowing rapid establishment of oceans and lakes

These results, published in the journal Earth and Planetary Science Lettersallow to define the atmospheric conditions…

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