ESA has published some images of an ancient system of trenches and river valleys near a large crater with a diameter of over 450 kilometers north of the great Hellas Planitia basin on the planet Mars obtained thanks to the Mars Express space probe’s High Resolution Stereo Camera (HRSC). The signs of water flow are mixed with the craters caused by impacts occurred between 3.5 and 4 billion years ago in that area of the Martian southern hemisphere showing the different processes that were taking place when the red planet was young and much more similar to the 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. Even the nearby areas suffered further impacts that have created other craters and there are other cases where their traces are mixed with those of water flows, so much that in September 2017 ESA published some photos of a nearby area where there was an impact in the mud.
This new case concerns a system of river valleys that are also north of Hellas Planitia and east of another large impact crater called Huygens. The topography of this region suggests that at the time the water flowed downhill from the north, which is on the right in the top image (ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO), to the south, which is on the left, carving valleys that had a length estimated up to two kilometers and a depth estimated up to two hundred meters. The erosion occurred during the long time that passed is visible in the valleys’ rims, which are smooth and fragmented, particularly in the valleys that go from east to west.
The morphology shows a tree-like structure that branches into various smaller and smaller channels. ESA used as a comparison the Yarlung Tsangpo River, the Tibetan part of the Brahmaputra River, which has a similar structure. In the case of the Martian river, probably the various channels were formed by the water of an important river flow also supplied by rainfall.
Reconstructing with precision the possible contributions of glaciers and rain to these ancient rivers is difficult but once again there are clear indications of a planet much more similar to the Earth. When Mars was young, it had a magnetic field that protected its atmosphere from solar wind, but it’s a planet about half the size of the Earth that cooled down relatively quickly losing that shield and slowly its atmosphere got eroded leading to a climate collapse.
All the discoveries of the recent years show that Mars was a planet that could host lifeforms similar to the Earth’s but it’s really difficult to understand if they ever really emerged. ESA continues to investigate with the ExoMars mission, which is being carried out together with the Russian space agency Roscosmos, with the launch a new rover scheduled for 2020 to conduct on-site surveys in the hope of finding some new clues.