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Volcanism may have triggered water flow on early Mars

Volcanic Mars Volcanic eruptions could have kept Mars warm enough for liquid water to intermittently flow across its ancient surface, suggests a new study.

The new findings, reported in Nature Geoscience, could explain the discrepancy between climate models showing Mars was never capable of having liquid water on its surface, and clear geological signatures of lake beds and river valleys formed by flowing water.

"There's indisputable evidence that Mars was once warm enough for liquid water to flow on its surface," says one of the study's authors, Professor James Head of Brown University in Providence Rhode Island.

"It's difficult to reconcile this fact with the latest generation of very robust climate models, showing Mars was always very cold and very icy, with an atmosphere too thin to heat the planet enough for water to flow."

The picture of a warmer early Mars is further complicated by the Sun also being much dimmer billions of years ago than it is today.

Head and the study's lead author Dr Itay Halevy of the Weizmann Institute in Tel Aviv, found there was a huge increase in volcanic activity on Mars about 3.7 billion years ago, the same time as water flowed on the red planet's surface, forming river valleys, deltas and lakes.

Significant volcanic eruptions on Earth can cause cooling rather than warming, as sulfuric acid particles and thick ash plumes either absorb solar radiation or reflect it back into space, lowering temperatures.

But dust in the Martian atmosphere mitigates the cooling effect, says Head.

"We looked at Mars' early atmosphere being dusty, and our calculations suggest a lot of the [volcanic plume] minerals like sulfur dioxide and sulfuric acid will adhere to these dust particles, reducing their ability to reflect the Sun's rays, delaying cooling," he explains.

Martian lava lakes

The authors found brief periods of intense volcanic activity would have pumped significant levels of greenhouse-inducing sulfur dioxide gas into the atmosphere, warming the Martian equatorial region sufficiently for liquid water to flow.

"We calculate that 30 per cent of Mars was resurfaced by lava flows, that's a lot of lava, and it can erupt over relatively short periods of time," says Head.

"It comes out as flood basalts and can have a huge affect on a planet's atmosphere."

Similar flood basalt formations on Earth, such as India's Deccan traps, and the Siberian traps in Russia, covered thousands of square kilometres, and are thought to have been caused by deep mantle plumes.

"If you bring the temperature up above freezing for decades to centuries, that melts enough ice and snow to produce the geological features we see in Martian valley networks and open basin lakes, even in a cold and icy early Mars," says Head.

Martian Antarctic

Head thinks the climate on early Mars may have some similarities to the cold, desert-like McMurdo dry valleys he's studied in Antarctica.

"The average yearly temperature in the Antarctic dry valleys is way below freezing, but peak summer daytime temperatures can exceed the melting point of water, forming transient streams, which then refreeze," says Head.

"In a similar manner, we find that volcanism can bring the temperature on early Mars above the melting point for decades to centuries at a time causing episodic periods of stream and lake formation."

The research may provide new clues about where to look for the fossilised remnants of any life forms that might once have existed on Mars.

"Microbial algae matts in Antarctica are resistant to the solar radiation and extreme cold and dry conditions," says Head.

"They sit there and just wait for the water to come, and when the water does come, they burst into bloom, so to speak. At other times they just dry up and get blown about to new locations by the wind where they wait for more water.

"Thus, the ancient and currently dry and barren river and lake floors on Mars may harbor the remnants of similar primitive life, if it ever occurred on Mars."