New analysis points to ancient Martian ocean, river valleys

NASA-funded boffins say they have found convincing evidence that much of Mars was once covered by an ocean of liquid water, and that rain fell on the red planet long ago.

The new research comes from scientists at Northern Illinois University and the Lunar and Planetary Institute in Houston, who have done a new computer analysis of valley networks on the fourth planet. The new picture indicates more and longer valleys than had previously been generally supposed, and further, that the valley networks tend to be concentrated in a belt round the planet south of the equator.

This, according to the scientists, provides backing for the already much-discussed theory that much of Mars' northern hemisphere was once an ocean. Rain falling in the south would have carved the valleys of the belt as it flowed toward the sea.

“All the evidence gathered by analyzing the valley network on the new map points to a particular climate scenario on early Mars,” says NIU geography prof Wei Luo. “It would have included rainfall and the existence of an ocean covering most of the northern hemisphere, or about one-third of the planet's surface.”

“The presence of more valleys indicates that it most likely rained on ancient Mars, while the global pattern showing this belt of valleys could be explained if there was a big northern ocean,” adds his collaborator Tomasz Stepinski, staff scientist at the Lunar and Planetary Institute.

Boffins have long argued over what formed the valleys of Mars, with some contending that it had to be rain runoff as is typically - but not always - the case on Earth. This would mean a wet, possibly life-bearing past for the nowadays largely airless and arid red planet.

Other scientists contend that other processes - ones which can occur in dry conditions - may have led to the valleys' formation. But Lou and Stepinski are having none of that.

“It is now difficult to argue against runoff erosion as the major mechanism of Martian valley network formation,” says Luo.

The two profs believe that rain would have mostly fallen on the northern ocean and the landmass near it, with very few rainclouds managing to get as far as the southern polar region. That would have been a desert even in the red planet's remote past.

The research paper, Computer-Generated Global Map of Valley Networks on Mars, is published for subscribers to the Journal of Geophysical research - Planets here. ®