Cyclical Water Presence Over Hundreds of Millions of Years

Scientists have long wondered about the presence and absence of water on Mars. Recent studies suggest that water on the red planet has not been constant, but rather has fluctuated over hundreds of millions of years.

Using impact craters, a planetary scientist from the United States learned how long ago networks of valleys formed by water formed on Mars, and also found out that rivers flowed regularly on the Martian surface, and not just in the earliest era.

The scientist’s discovery will not only change the established understanding of the Martian landscape, but will also reveal some secrets of the climatic history of the Red Planet.

Today, Mars is a desert world, virtually defenseless against cosmic rays. The atmosphere there, although it consists of 95 percent carbon dioxide, is very rarefied, so it is not able to retain heat for a long time even with this greenhouse gas content.

Because of this, it is cold on the Red Planet: the average temperature is minus 63 degrees Celsius (minimums are up to minus 125), however, in the summer during the daytime it can rise to plus 25 or even plus 30 near the equator.

Mars hasn’t always been an “unfriendly” place. The planet had a dense atmosphere, and the climate there was humid and warm, it rained, and rivers flowed across the surface. Researchers believe that the Red Planet lost its “heavenly beauty” about three billion years ago.

Then some event occurred there, due to which the magnetic field disappeared, the main part of the atmosphere disappeared somewhere: it was either carried away by the solar wind, or bound by soil, and the water turned into subsurface ice.

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This is how Earth’s neighbor became the cold and dry world that scientists observe today.

How do we know that rivers flowed on Mars? Following the traces of water found by rovers and orbital stations. One piece of evidence is the network of valleys.

Valleys of Nergal, photographed by Mariner 9 / © NASA

They are branched systems of canals ranging from hundreds of meters to 20 kilometers wide and up to hundreds of meters deep. Researchers believe that these networks appeared due to surface runoff, as a result of large lake spills, and river activity.

According to a number of experts, such canal systems were formed more than three billion years ago, at the end of the Noachian – beginning of the Hesperia era.

However, the total period of time it took for these objects to form is not precisely known. Most attempts to determine this time have relied on the intermittency coefficient, which can be used to study “living” Earth rivers, but not for “dead” Martian ones. In previous work, experts have suggested that erosion processes caused by surface water flows occurred in the areas where the canals are now located over several tens of thousands of years.

American planetary scientist Alexander Morgan from the Planetary Science Institute (USA) tried to find out exactly how long it took for the Martian valley networks to form.

In his study, published in the journal Earth and Planetary Science Letters, the scientist said that these valleys probably did not form quickly, not over tens of thousands of years, but very slowly, over hundreds of millions.

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Moreover, their formation was accompanied by long dry periods. That is, the rivers flowed, then at some point their beds dried up, and then filled up again. How many such “cycles” there were is still a mystery.

As a dating tool, Morgan used impact craters located on eight sites on Mars with a total area of ​​10 thousand square kilometers. The scientist identified and determined the age of populations of impact craters that appeared before and after the formation of the valley network. This allowed the planetary scientist to obtain the maximum time frame for the formation of river channels.

In the work, the American scientist noted that the “lifespan” of Martian rivers may have been relatively short: they flowed for only 0.001 percent of the lifetime of the valley network.

This means that, in general, the rivers on Mars constantly dried up, but they could “wax up” again due to volcanic activity, snow melting, or changes in the inclination of the rotation axis and orbit of the Red Planet.

Such climatic fluctuations also occur on Earth – they are called Milankovitch cycles. They explain the natural climate changes occurring on our planet and cause periodic glaciations.

As for the slow rate of valley formation, the scientist believes that the reason for this is the accumulation of large boulders in river beds, which slowed down erosion.

Morgan concluded: “If the Martian river valleys really formed over hundreds of millions of years, it means that favorable conditions for the emergence of life existed there longer. That is, longer than previously thought.

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“The likelihood of life appearing and developing is higher in an environment where liquid water exists for a long time.”

The study was published in the Earth and Planetary Science Letters journal.

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