A rather convincing confirmation of the fact that once upon a time there was water on Mars is the image of an ancient, dried up channel imprinted on the surface of the Red Planet. Although this find was exposed to the weak Martian winds for hundreds of thousands or even millions of years, the channel is perfectly preserved and is an excellent source for studying the history of the planet.
Located in the Atzilali plain, a region predominantly located north of the Martian equator, this river seemed to flow from right to left, down the side of the crater and towards the crater itself. This image was taken on September 25, 2015 with the High-Resolution Imaging Science Experiment (HiRISE) onboard the NASA Mars Reconnaissance Orbiter (MRO). No one knows how long the water flowed in this ancient river, and its source, it is only known that the water channels converged rapidly at the bottom of the crater, meandering on the plain. This “tree-like” riverbed consists of many small tributaries that were fed from the primary channel, according to Mike Mellon from the HiRISE team.
There is no full understanding of the source of such rivers - from underground aquifers, meltwater or even precipitation - but with the help of studies of large dried up rivers of Mars from orbit, we can supplement the results of studies of surface missions (for example, NASA's Curiosity and Opportunity rovers) to Put together the puzzle of Mars' water past.