Mars valleys linked to heavy rainfall

The angles of valley branches - here a section of the Warrego Valles region - on Mars are narrow and correspond to those of arid regions on Earth. (Image: NASA / JPL / ASU)

Valleys on Mars strongly resemble those in arid regions on Earth, suggesting that the Red Planet used to experience long periods of heavy precipitation and erosion, Swiss researchers believe. 

For years the scientific community has been studying the question of water on Mars. Was it rainwater that caused streams and rivers to swell? Or did ice in the soil melt due to volcanic activity, and seep out to form rivers? 

A new study now suggests that the branching structure of former river networks on the Red Planet has parallels with terrestrial arid landscapes. This was revealed in a paper published in Science AdvancesExternal link by physicists Hansjörg Seybold and James Kirchner from ETH Zurich’s Institute for Terrestrial Ecosystems, and planetary scientist Edwin Kite from the University of Chicago. 

Using statistics from all mapped river valleys on Mars, the researchers conclude that the contours still visible today must have been created by surface run-off rainwater. They exclude the influence of groundwater or meltwater from the soil as the main process for shaping the landscape. 

Seybold believes that there must have been sporadic heavy rainfall events on Mars over prolonged periods and that this rainwater may have run off quickly over the surface shaping the valley networks. This is how river valleys develop in arid regions on Earth such as in Arizona in the United States. 

The scientists believe that conditions such as those found in terrestrial arid landscapes today probably prevailed on Mars for only a relatively short period about 3.6 to 3.8 billion years ago. During that time the atmosphere on Mars may have been much denser than it is today. 

“Recent research shows that there must have been much more water on Mars than previously assumed,” says Seybold. 

One hypothesis is that the northern third of Mars was covered by an ocean at that time. Water evaporated, condensed around the volcanoes of the highlands to the south of the ocean and led to heavy rainfall there. As a result, rivers formed, which left the traces that can be observed on Mars today. 

However, it is still unclear where the water may have disappeared to over time. 

“It’s likely that most of it evaporated into space. Traces of it might still remain in the vicinity of Mars,” says the physicist.