The pictures from Mars can be seen that its surface is dotted with channels, which are the remains of an extensive system of streams and rivers. The beds of these rivers are a rich source of information about the water passing through them and the climate of ancient Mars. For example, the width and steepness of the river bed and the size of the gravel make it possible to understand the strength of the flow of water. Determining the parameters of such rivers is one of the tasks in creating models of the evolution of the planet’s climate.
Today, scientists do not have a complete understanding of how the Martian climate changed billions of years ago. It is believed that in the later periods of the history of Mars (Hesperian and Amazonian), when the atmosphere became thin, precipitation could fall out only in a few places, or they were no longer at all. At the same time, water could still form: for example, when asteroids were falling, causing ice to melt and release of underground sources. However, the study of sediments with the Curiosity rover shows that more water was needed to create the existing channels than could be caused by the fall of the asteroids. At the same time, the deposits of ancient rivers and lakes show features of formation in the late climate stage, which was dry or had short wet periods. Such a contradiction complicates the modeling of the climate of Mars.
In an effort to understand the origin of Martian sediments, scientists from the University of Chicago analyzed photographs from the global database of fan-shaped alluvial sediments and deltas, as well as digital terrain models based on HiRISE cameras mounted onboard the Mars Reconnaissance Orbiter spacecraft. In total, scientists have analyzed more than 200 ancient Martian channels, spanning over a billion years. Scientists have scaled the size of the channels of the ancient rivers of Mars, using them as an indirect indicator of the formation of water flows in the past, and then compared with the channels of the Earth's rivers from a large database of rivers and water basins of the United States. The researchers also calculated the intensity of the flow of rivers using several methods, including analysis of the size of river channels. In the river basins, for which there is the greatest amount of data, the rivers of Mars were about two times wider than on Earth. And between 3.6 and 1 billion years old and, probably, even after 1 billion years ago, the climate was periodically becoming wet — then the water flow could be from 3 to 20 kilograms per square meter every day.
In addition, scientists found that late-stage rivers began to form lower, and their distribution was severely limited in latitudes, which is consistent with climate models where the air pressure after the loss of the atmosphere fell less than 1 bar. This is important, as many other models take into account the pressure of more than 1 bar when forming rivers. In addition, the deep river erosion of the late stage of the Hesperian period included small rivers that were more concentrated on the ground than the regional river networks of an earlier stage, which covered the entire planet. Movement of water occurred throughout the planet and was not a short-term or local phenomenon. One possible explanation for the conflict between the slow removal of the atmosphere at a late stage and high river flows is that the climate was caused by one or several natural mechanisms that caused strong warming at low pressure. For example, the greenhouse effect from the abundant melting of glaciers. If the dates for the existence of these massive rivers are correct, then, according to the researchers, it can be assumed that the atmosphere of the late stage of Mars disappeared faster than previously calculated. Or, perhaps, there were other climatic factors of precipitation in a low atmosphere. The results obtained impose new restrictions in the development of models of the evolution of the climate of Mars.
Previously, scientists have repeatedly reported the existence of water on Mars in the past. For example, scientists have concluded that the grooves on the stone slabs, discovered by "Curiosity", may be left after the evaporation of water by mud cracks. In addition, scientists have discovered an ice-covered reservoir at the south pole of Mars.
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