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 discovered how long ago networks of valleys formed by water formed on Mars, and also discovered that rivers regularly flowed on the surface of Mars, and not only in the earliest epoch.
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 radiation. The atmosphere there, although composed of 95 percent carbon dioxide, is very thin and therefore cannot retain heat for long even with this greenhouse gas content.
This makes it cold on the Red Planet: the average temperature is minus 63 degrees Celsius (minimums go up to minus 125), but in summer it can rise to plus 25 or even plus 30 during the day 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 over its surface. Researchers believe that the Red Planet lost its “heavenly beauty” about three billion years ago.
Then an event occurred there, as a result of which the magnetic field disappeared, most of the atmosphere disappeared somewhere: it was either carried away by the solar wind, or bound by the ground, and the water turned into underground ice.
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? We follow the trails of water found by rovers and orbital stations. One piece of evidence is the network of valleys.
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They are branched canal systems ranging from hundreds of meters to 20 kilometers wide and up to hundreds of meters deep. Researchers believe these networks formed as a result of surface runoff, resulting from 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 time it took to form these objects is not exactly known. Most attempts to determine this time are based on the intermittent coefficient, which can be used to study “living” rivers on Earth, but not “dead” rivers on Mars. In previous work, experts have suggested that erosion processes, caused by surface water flows, have occurred for several tens of thousands of years in the areas where the channels are now located.
American planetary scientist Alexander Morgan of the Planetary Science Institute (USA) tried to find out exactly how long it took for the Martian valley networks to form.
In his research, published in the journal Earth and Planetary Science Letters, the scientist said these valleys probably did not form quickly, not over tens of thousands of years, but very slowly, over hundreds of millions of years.
In addition, their formation was accompanied by long dry periods. That is, the rivers flowed, at some point their beds dried up and then filled again. How many such ‘cycles’ there were is still a mystery.
As a dating tool, Morgan used impact craters at eight locations on Mars covering a total area of 10,000 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 “life” of rivers on Mars may have been relatively short: they flowed for only 0.001 percent of the life of the valley network.
This means that rivers on Mars generally dry up continuously, but they can ‘dry up’ again due to volcanic activity, snowmelt, or changes in the tilt of the Red Planet’s rotation axis and orbit.
Such climate fluctuations also occur on Earth – they are called Milankovitch cycles. They explain the natural climate changes that occur on our planet and cause periodic ice ages.
As for the slow formation of valleys, the scientist believes that the reason for this is the accumulation of large boulders in river beds, which slow down erosion.
Morgan concluded: ‘If Mars’ river valleys really formed over hundreds of millions of years, that means favorable conditions for life to emerge existed for longer. That is to say: longer than previously thought.
“Life is more likely to appear and develop in an environment where liquid water exists for a long time.”
The research was published in the Earth and Planetary Science Letters Journal.