An article published in the journal “Nature Communications” reports evidence of the existence of a river of a size comparable to that of the great European rivers such as Po and Rhine in the Izola mensa area, an outcrop within the large Hellas Planitia basin on the planet Mars. A team of researchers led by Dr. Francesco Salese and Dr. William McMahon examined high-resolution images captured by NASA’s Mars Reconnaissance Orbiter (MRO) space probe to identify traces of an area where some 3.7 billion years ago there was a large river. The environmental conditions had to be favorable to a constant flow of water for a long period with a hydrological cycle, yet another confirmation that at the time the red planet was similar to Earth.
The Hellas Planitia basin is the largest of Mars generated by an impact since it’s itself a crater, with a diameter of about 2,300 kilometers and a depth of about 7 kilometers. It dates back to the period of late heavy bombardment between 4.1 and 3.8 billion years ago, when the inner planets were struck by a particularly high amount of asteroids and comets. It contains sediments dating back to around 3.7 billion years ago and lava flows generated by volcanic activity dating back to around 3.3 billion years ago.
The ancient traces existing in Hellas Planitia and also in the nearby areas are interesting because the sediments date back to an era when Mars was similar to the Earth. To the north of that large basin there was a river system at the time, and now in the outcrop called Izola mensa a team of researchers found traces of another river. That outcrop on the basin’s northwestern rim is about 200 meters high and about 1.5 kilometers wide, and its layers show the ancient geological traces that are extraordinarily similar to the sedimentary rocks existing on Earth.
For years Hellas Planitia has been studied by planetary scientists for the ancient traces dating back to the Noachian era, a Martian geological era between 3.7 and 4.1 billion years ago. They indicate that it hosted what was at least a large lake if not a sea. Now geologists Francesco Salese and William McMahon brought evidence that the traces of a large river were preserved in the outcrop of Izola mensa.
The geological traces indicate that the water flow lasted for many millennia, with a course that changed over time, and maybe it flowed right into the lake that existed in Hellas Planitia. All this meant that there were conditions suitable for maintaining liquid water courses with a hydrological cycle based also on rainfall.
This reconstruction is consistent with that relating to the presence of liquid water in many other areas of Mars in the form of rivers, lakes, and seas. According to Francesco Salese, it’s a crucial type of evidence for the search for ancient Martian life forms. Each new lander and rover mission comes with new instruments that have also this purpose.
