Most of the lakes on Mars have not been identified

Most of the lakes on Mars have not been identified

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If the presence of liquid water in Mars’ past is no longer in doubt, a new study underlines that we are far from having identified most of the lakes that existed on the Red Planet.

For some time now, and in particular thanks to data collected by Mars rovers, we have known that Mars once had lakes of liquid water, often nested in the hearts of ancient impact craters. The Jezero crater, which Perseverance is currently traversing, is a perfect example of this, particularly with the presence of a deltaic sedimentary succession.

The study of these ancient lakes, whose existence dates back several billion years, is extremely important to determine the climatic conditions that prevailed on the planet at the beginning of its history. They are also favorite places to hope to find traces of primitive life. Because lacustrine sediments, often clayey, are the most favorable environments for the conservation of biological molecules.

Ancient Martian lakes are identified, of course, thanks to satellite data and images acquired from orbit by the various probes that constantly scan the Martian surface. Today, about 500 ancient lakes have been listed on the surface of Mars. But for some scientists, this figure is certainly far below reality.

70% of ancient Martian lakes still unidentified

In fact, more than 1,000 Paleolacs could have escaped the eye of the satellites. It all sounds like one big story. It should be noted that almost all of the ancient lakes identified so far are particularly large, usually over 100 km.two. However, on Earth, only 30% of lakes fall into this category. The remaining 70% are much smaller.

If we take this statistic to hold for the Red Planet, it’s very likely that we’ve missed the vast majority of Martian lakes so far. This gap could simply be explained by the difficulty of identifying these small ancient basins using satellite images. However, they could, like larger lakes, provide a wealth of information about the Red Planet’s past environment.

Ephemeral and short-lived lakes

This issue was the subject of an article in the magazine nature astronomy. For Joseph Michalski, from the University of Hong Kong and lead author of the study, referring to all the ancient lakes could, in particular, make it possible to better date the presence of liquid water on the planet’s surface, but also better understand global water. conditions and their variations over time. Because if the currently identified lakes are between 3.5 and 4 billion years old, it seems that each lake would only have had a lifespan of the order of 10,000 to 100,000 years. This means that most of the time the planet would have been arid and cold, with only episodic warm periods during which the lakes would have formed ephemerally.

Martian lakes would also be relatively different from those observed on Earth. In fact, the low gravity of the planet would not have favored the rapid deposition of sediments on the bottom. Instead of crystalline lakes, it would seem more accurate to imagine lakes with cloudy waters, loaded with sediments, and in which the pale light of the young Sun would have had difficulty penetrating. The absence of vegetation, which normally helps to stabilize the sediments, would also have favored this phenomenon. Add to that the fact that remote Mars receives much less solar energy than Earth and has a lake environment that is certainly not conducive to the development of photosynthetic life.

The best chances of finding biosignatures remain in large, deep lakes

In this context, and even if all the ancient Martian lakes are far from being identified, the great lakes remain the most interesting places to visit to find biosignatures. In fact, they are the ones that have probably been in the water for long periods of time. They also have the advantage of presenting various types of environments, with the potential presence of hydrothermal systems capable of providing a source of heat and energy that supports the appearance of microbial life.

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