Massive volcanic eruptions on Mars allowed ancient oceans to form, say scientists

Mars was once covered by oceans due in part to the activity of vast volcanoes on the planet’s surface, according to a new study.

Shoreline-like structures found on the Red Planet have led scientists to infer its northern lowlands were once filled by water.

However, their unusual geology led others to call the theory into question.

Now, work by a team at the University of California, Berkeley, suggests oceans were indeed found on Mars, and their presence was linked with massive volcanic activity billions of years ago.

"Volcanoes may be important in creating the conditions for Mars to be wet," said Professor Michael Manga, a planetary scientist at the University of California, Berkeley, who led the research.

The new study, published in the journal Nature, suggests oceans on Mars actually formed several hundred million years earlier than scientists previously thought – over 3.7 billion years ago.

This formation was linked to the creation of Tharsis, a 5,000-kilometre-wide structure containing some of the largest volcanoes in the solar system.

The scientists suggest that as Tharsis emerged, its eruptions released gases that altered the atmosphere and enabled liquid water to persist on the planet’s surface.

At the same time, the eruptions would have created channels that allowed underground water to fill the northern plains of Mars from below the planet’s crust.

Key to the new theory offered by Professor Manga and his team is their explanation for the unusual “shorelines” seen on Mars today.

While these structures certainly look like dried-up shorelines, they are very irregular – varying in height by as much as a kilometre. Normally coastlines are fairly constant in their elevation, so this has perplexed researchers looking for evidence of ancient oceans.

Professor Manga and his colleagues suggest this anomaly can be attributed to the Tharsis volcanoes, which would have deformed the shorelines as they emerged from the planet’s surface and led to their varying heights.

Scientists previously suggested that if the oceans on Mars did exist, they formed after the emergence of Tharsis.

"The assumption was that Tharsis formed quickly and early, rather than gradually, and that the oceans came later," said Professor Manga.

"We're saying that the oceans predate and accompany the lava outpourings that made Tharsis."

This timing accounts for discrepancies in the amount of water found today frozen in the planet’s polar ice caps and the amount that would have been required to fill the ancient Martian oceans.

Tharsis is a major feature on the surface of Mars, covering around 25 per cent of its surface area and creating a large bulge on the side of the planet, as well as a massive depression.

If the oceans existed before Tharsis reached its full size, they would not have had to fill this depression and could therefore have been much shallower.

This means oceans could have formed with only half the amount of water previously estimated.

While Professor Manga pointed out their idea is only a hypothesis, he said by precisely dating Tharsis and the planet’s ancient shorelines scientists would be able to determine if it holds up.

When Nasa’s next Mars lander heads to the Red Planet in May, it may be able to reach some more satisfactory conclusions about water on Mars.

It will place a seismograph on the planet’s surface to investigate the interior of the planet, and potentially find frozen remnants on its ancient oceans.