The Martian landscape is crisscrossed by a complex network of valleys that bear a close resemblance to the fluvial stream channels dug by rivers on Earth.
While most scientists agree that the valleys on Mars were created by water billions of years ago, it has been difficult to establish the exact source of this water on a planet that's probably been arid for more than 600 million years, as reported by SciTech Daily a while back.
The two main hypotheses are that these geological features were left behind either by subsurface water ice, which melted under the influence of the planet's volcanic activity and repeatedly seeped from beneath the crust to form rivers or by massive precipitations over a long period on time.
A team of researchers from Switzerland and the United States believe they have finally solved the mystery and point to heavy rainfall as the more obvious culprit.
According to their study, published this week in the journal Science Advances, the network of valleys that slither all over Mars was not carved by re-emerging groundwater, but by large amounts of precipitations that showered the Red Planet some 3.8 billion years ago.
"Recent research shows that there must have been much more water on Mars than previously assumed," says study lead author Hansjörg Seybold, a physicist at ETH Zurich in Switzerland.These massive downpours, which most likely fell in huge spells 3.6 to 3.8 billion years ago, fed a vast network of rivers that ended up carving the puzzling valleys on Mars, explains ETH Zurich in a news release.
While those ancient rivers have long dried up — Seybold says that most of them likely "evaporated into space," though some of the water "could still be found in the vicinity of Mars" — the network of valleys still endures and can be seen in various places on the Martian surface.
One such example is Osuga Valles (pictured below) south of Eos Chaos — "chaos" is a term attributed by NASA to portions of rugged and broken terrain on Mars, the Inquisitr recently reported — which runs a total length of 164 kilometers (almost 102 miles).
This Martian valley measures up to 20 kilometers (nearly 12.5 miles) across in some places and plunges as deep as 900 meters (approximately 3,000 feet), notes the European Space Agency.
To reach their conclusions, the scientists combed through statistics of all the mapped valleys on the Red Planet and looked at the angles at which these valleys branch out, comparing them to the ones found on Earth.
They then turned to previous studies on the branching angles and learned that river valleys in arid territories — such as the ones found in Arizona, in an area used by astronauts to train for future Mars missions — typically have lower branching angles. At the same time, valleys in more humid landscapes carved by re-emerging groundwater, like the ones seen in Florida, usually branch at wider angles.
Their investigation revealed that the valleys on Mars are very similar to the ones carved in arid regions on our home planet, meaning that they could only have been created by "superficial run-off of (rain)water" trailing on the Red Planet's surface — and not from subsurface water flowing outward from within."We find that valley networks on Mars generally tend to branch at narrow angles similar to those found in arid landscapes on Earth. This result supports the inference that Mars once had an active hydrologic cycle and that Mars' valley networks were formed primarily by overland flow erosion, with groundwater seepage playing only a minor role," the team wrote in the study.
So, what triggered the heavy rain on Mars? The most plausible scenario is that the Red Planet was once covered by a vast ocean, stretching over the northern third of its surface, explains the Swiss university.
"Water evaporated, condensed around the high volcanoes of the highlands to the south of the ocean and led to heavy precipitation. As a result, rivers formed, which left traces that can still be observed on Mars today."