The recent Martian Perseverance mission has rekindled interest in the search for traces of the presence of water on Mars.

However already with the Curiosity mission, landed on the red planet il 6 August 2012, Interesting discoveries have been made on the possible presence of ancient waterways that, more than 3 billions of years ago, they would have plowed the surface of the planet.

Along the exploratory journey made in the Gale crater, located below the Martian equator and originated around 3,6 billions of years ago, the Curiosity rover has identified and photographed several rocks with an interesting structure.
These are sedimentary rocks composed of rounded pebbles, held together by a compact matrix, very similar to the conglomeratic rocks of fluvial origin that we find on earth.

On our planet, conglomerates originate from the disintegration of pre-existing rocks, that due to various physico-chemical processes, such as rain, wind, sudden changes in temperature etc., are eroded, to then be transported by gravity or by water flowing to the surface.
The movement of these sediments by means of water courses causes the progressive rounding of the pebbles, also referred to as clasts, pushed by the force of water, they are transported for kilometers.

The roundness of the Martian clasts therefore suggests that more than 3 billions of years ago there was a watercourse that crossed the Gale crater, which extends for approx 155 km, partially eroding it and giving rise to the rocks found by Curiosity.

This fact seems to be confirmed by the analysis of the photos taken by the probe in different points of its path.

Scientists noted that the degree of roundness of the clasts varies, becoming progressively less pronounced moving north. In addition, also the bruising of the clasts, which is the geometric arrangement between the pebbles within the rock, would confirm the presence of a flow of water that went from north to south.

The ancient stream would then have crossed the crater from the north, eroding a part of it and transporting the sediments thus created towards the center of Gale.

In the near future it will also be interesting to compare the data obtained from the Perseverance rover, who is currently exploring the Jezero crater, one of the most promising areas to find traces of waterways and who knows, maybe even traces of life!

Sources:

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2013JE004435

https://www.nasa.gov/mission_pages/msl/multimedia/pia16189.html

https://www.nature.com/articles/ncomms9366