The photos of Mars taken by ESA's Mars Express spacecraft show traces of liquid water flowing across the surface of the planet. The incredible satellite images reveal an ancient and complex system of trenches, valleys and dry riverbeds. The discovery points to a Martian past where conditions were much warmer and wetter than today. And although Mars can no longer receive liquid water on the surface, a clearer picture of the history of the red planet appears.
ESA said in a statement: "We view Mars as a dry, cold world, but there is plenty of evidence to suggest that this has not always been the case.
"Research in recent years has increasingly indicated that the planet has a thicker and denser atmosphere, capable of capturing much more heat and therefore facilitating and supporting the flow of liquid water to the surface.
"Although this is no longer the case, we see clear signs of past water activity on the Martian surface."
ESA's photographs show an ancient network of waterways in a southern region of Mars near the famous Huygens crater.
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Water on Mars: These incredible photos are evidence of an ancient water on the red planet
It is estimated that this region of Mars is between 3.5 and 4 billion years old and is one of the most marked regions of the planet.
We see clear signs of activity of the past water on the Martian surface
In this mountainous region north of the Plains of Hellas Planitia lies the most convincing proof of the wet history of Mars.
Topographic analyzes suggest that the region's water flowed from north to south.
The running water was probably responsible for the formation of visible valleys in the ESA photos.
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Some of these valleys measure up to 2 km wide and 200 meters deep.
ESA said, "We are seeing these valleys as they are today, having suffered significant and significant erosion since their formation.
"This erosion is visible in the form of decomposed, smoothed, fragmented and dissected valley edges, especially in the valleys that are widening from east to west.
"Overall, the valley system seems to branch out significantly, forming a pattern much like branches of trees stemming from a central trunk."
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Water on Mars: The red planet was once warmer and much wetter than today.
There are identical systems on Earth, such as the Yarlung Tsangpo River, which crosses western Tibet through China, India and Bangladesh.
In the case of Mars, ESA stated that the branched waterways were most likely the result of surface water runoff from strong rivers and heavy rains.
The running water would have been powerful enough to cross the Martian rock for many years, creating new paths and waterways.
But what does all this mean for the search for life on Mars? Does a warmer, wetter past indicate that life has evolved on the red planet in the same way as on Mars?
ESA said: "This warmer and wetter climate raises the question of whether conditions would have been conducive to life – a subject at the heart of Mars exploration.
"Next year, ESA and Roscosmos will launch the ExoMars mission including a rover – recently named Rosalind Franklin – and a surface science platform.
"The rover will travel to interesting places to drill under the surface for signs of life – the first mission of its kind."
The European Space Agency (ESA) said that scientists are studying ways to collect rock samples and send them to Earth.
The most likely scenario is that scientists someday discover evidence of microbial life on Mars – not necessarily full-fledged, intelligent civilizations.
Water on Mars: the discovery strengthens the hope of one day finding microbial life on Mars
Ellen Stofan, former director of NASA, voiced this view before a sub-committee of the US Senate when she was asked about the future of NASA's research in space.
According to the scientist, it will take a long time and "break stones", but astronauts will one day find evidence of microbial life on Mars.
The scientist: "Life has rapidly increased here on Earth once conditions have stabilized. You know, for hundreds of millions of years, the conditions were probably hostile.
"This is as soon as the situation stabilized after about 100 million years, and we are confident enough that the first microbial life has evolved on Earth.
"The problem is that life has remained in the oceans for a billion years and that it has taken well over a billion years for life to become more complex. That's why I'm optimistic and my life has evolved on Mars. "