Sf the presence of liquid water on the surface of the young planet Mars, 4 billion years ago, is hardly in doubt, the duration during which it was able to maintain itself, and in what proportion, still remains a subject of controversy among scientists. Was there ever an ocean on Mars and how long could it persist? These two questions remain burning insofar as the quantity of bodies of water but also, and perhaps above all, the duration during which they could exist on Mars are major factors for its habitability and the emergence of life.
Since the 1980s, scientists have identified what looks like an ancient shoreline and, since then, flows up the slopes that can testify to violent tsunamis. However, their attempt to reconstruct the ancient climate of Mars had so far never led to conditions authorizing the existence of this ocean and especially not its persistence over time. According to these simulations, all available water would inexorably accumulate in the form of snow on the mountains. But the situation has just changed!
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Two new parameters
Indeed, an international team of researchers, including French people from the Paris-Saclay geosciences laboratory (Geops, CNRS-Paris-Saclay University), has finally come to a simulation that can authorize the existence of an ocean in the hemisphere. north of the red planet. As big as ten times the Mediterranean Sea, it could even have covered more than 15% of the surface of Mars, at an average depth of 2,000 to 3,000 meters, and this, until 3 billion years ago!
To achieve this, these scientists integrated two elements that had never before been taken into account in the models: ocean circulation and the evolution of glaciers. In other words, the possibility that the waters coming from the middle latitudes have circulated to warm those of the polar zone and also the fact that glaciers have been able to bring water from the heights towards the ocean. Enough to keep it stable over a relatively long period.
That would be great news. Indeed, if this scenario is confirmed, before becoming the arid desert that it is today, the planet Mars could have been largely conducive to the development of life, at a time when it abounded on Earth.