Images taken by the European Space Agency’s Mars Express satellite show the marks that an ancient network of rivers have left on the planet’s surface.
The valleys formed as they would on earth, with a strong flow of water carving its way through the landscape.
What is less clear is where the water came from. Due to a lack of knowledge about the past climate of Mars, scientists can not tell whether it came from groundwater, precipitation, melting glaciers or something unheard of.
There is no liquid water on the surface of mars today, though plenty of similar ex-water features have been discovered in recent years, suggesting Mars once had a far wetter and warmer climate.
Each discovery raises further questions about the planet’s past atmosphere and scientists ultimately want to know whether or not it would have been suitable for life.