An article published in the journal “Science Advances” reports the results of a research on the ancient rivers that existed on the planet Mars that lead to think that they existed until less than a billion years ago. A team of researchers coordinated by the University of Chicago cataloged over 200 ancient rivers by analyzing model and photos showing the traces of their beds to obtain a conclusion that goes against what the scientists who studied the red planet generally think of, that is, rivers and rainfall disappeared over 3 billion years ago.

The reconstruction of Mars’ history is still very incomplete therefore every geological trace detected by one of the space probes in orbit and any analysis performed by a rover or a lander on the surface can add important details to shed light on important periods in the planet’s evolution. Among the certainties is the fact that what is today called the red planet because it’s a barren land was much more similar to the Earth when it was young, with seas, rivers and an atmosphere with rainfall. However, the general impression was that the cooling of the Martian core and the consequent loss of the magnetic field that protected it from the solar wind, the erosion of the atmosphere and the consequent climate collapse turned Mars into an arid planet with perhaps a last period of presence of rivers about 2 billion years ago. Maybe things aren’t exactly like that.

This new research exploited a series of digital elevation models of Martian areas created thanks to images captured by NASA’s Mars Reconnaissance Orbiter space probe’s High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) instruments. The many traces that still exist and are well preserved of ancient river channels allowed the researchers to calculate the intensity of the water discharge and their beds’ size. The amount of data was greater for some river basins and they indicate that those rivers were much larger than the Earth’s ones. The flows calculated for Martian rivers range from 3 to 20 kg of water per square meter per day, a situation that could have gone on up to a billion years ago at a global level.

These conclusions are truly surprising and raise new questions because they contradict our knowledge of Mars history. Edwin S. Kite of the University of Chicago, lead author of this research, recognizes the difficulty for the scientists who are trying to create models for the ancient Martian climate and the new difficulty added by his team’s conclusions. To explain the contradictions he hypothesized that on Mars there was an alternation of dry and wet climates which led the rivers to shorten from thousands to hundreds of kilometers but still having a considerable discharge.

Edwin S. Kite acknowledges that somewhere in the various studies there must be an error, in climate models, in the evolution patterns of the Martian atmosphere or in our basic understanding of the chronology of the inner solar system. Understanding the humidity levels changes in the Martian atmosphere in the course of its history is crucial to obtain certain answers. In essence, we still need data to get a clear idea that is close to the completeness of that history.