Mars once had rivers, and we just identified 16 of the largest for the first time
.The Red Planet was much more similar to Earth when it was born. It had oceans and seas until about 3 billion years ago, and it even had a drainage system of rivers from precipitation. On Earth, areas around rivers are hotspots of biological activity, and if Mars had life, it is expected to have thrived in such locations as well.
Waters in them carry vast amounts of nutrients that dissolve from rock and help fertilize seas and oceans. We don’t expect to find anything more than the simplest life forms on Mars if at all, but on Earth, rivers are even the birthplaces of human civilizations.
The 16 largest basins account for only about 5% of the Mars surface, but flowing water is known for intense erosion, and these areas have deep geological layers revealed by this destructive force. This means that they are the best places to obtain samples of ancient Mars to look for signs of microbial activity or even fossils.
This research was possible thanks to data on surface features that have been accumulated over the years but have never been used to identify rivers globally. We have known some ancient sites where lakes or river valleys might have existed, and these already-known areas helped piece together much larger networks. Each of the largest 16 river basins covered 100,000 square kilometers or more.
The diversity and extent of river basins on Mars are much smaller than on our planet. Earth has 91 that cover at least 100,000 square kilometers of land area. Although Mars is a much smaller world, our planet is 71% covered with water, and the total land area is comparable, 149 million square kilometers on Earth and 145 million on Mars.
In our world, rivers are constantly reshaped by plate tectonics, whereas on Mars, this powerful force is absent. This is one of the reasons river networks are less complex on the Red Planet.
Even though the 16 largest cover only about 5% of Mars's land area, they account for 42% of the eroded material formed by flowing water. Mars also had smaller rivers, but they were not as impactful.