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Mars might only be mostly dead (geologically speaking)

A new paper argues for the existence of an active mantle plume underneath the surface of Mars, leading to seismic and volcanic activity.

(CN) — “There's a big difference between mostly dead and all dead," according to the great film, The Princess Bride. "Mostly dead is slightly alive."

Until lately, Mars has been generally considered to be a dead planet — geologically speaking, that is. In stark contrast to Earth, with its constantly shifting tectonic plates and volcanic activity, Mars is just a big cold (and getting cooler by the day) rock, with nothing much going on underneath its dry, red surface. Or so we thought.

A growing number of data points suggest that Martian geology may be a bit more complicated. For one thing, the InSight robotic lander, which has been on the planet for more than four years, has detected more than a thousand marsquakes — a surprise, since we also believe that Mars has no tectonic plates to rub together.

And there was the the realization that the Cerberus Fossae, a series of long cracks or fissures on the surface of the planet, were formed by seismic activity and not, as previously thought, dislodged boulders. Photographs of the surface suggest a history of lava flowing on the surface of the planet. In certain areas, that volcanic activity wasn't too long ago.

Now, a new paper, published in Nature Astronomy on Monday, suggests a cause for all that: a massive, active mantle plume, with a diameter of nearly 2,500 miles, which may be lurking underneath the surface of the northern plains of Mars, pushing the crust upward and bringing hot magma to the surface.

Should this theory be proven true, it would radically alter our understanding of Mars.

"This is really a paradigm shift in our understanding of how Mars evolved," says one of the study's authors, Adrien Broquet, a postdoctoral research associate in the University of Arizona Lunar and Planetary Laboratory. "It’s very much not a dead planet today. It’s a dynamic planet and an alive planet."

What exactly is a mantle plume? Broquet says to think of it like a lava lamp: a plume of heat rising from the core of the planet, rising slowly through the mantle, heating the crust to form magma and, by the time it reaches the crust, lava. Mantle plumes are often believed to be the cause of anomalous volcanism — that is, volcanic activity in places you wouldn't expect, or unusually large volcanic activity, as seen in places like Hawaii and Yellowstone National Park.

As evidence for his theory, Broquet and his co-author, Jeff Andrews-Hanna, cite the presence of an enormous uplift on the surface of Mars, about a mile high and 2,500 miles across. The top of it is one of the highest elevations in Mars' northern hemisphere.

Broquet and Andrews-Hanna used this evidence of surface lava in the past, the fissures of Cerberus Fossae, the recently observed seismic activity and data about variations in Mars's gravitational field to build a statistical model, and found that a mantle plume explains all the observations.

Though the mantle plume theory may answer some questions, it raises others.

"This kind of scenario is definitely not explained by current thermal evolution models of the planet," said Broquet. "It's difficult to explain."

There is believed to be millions of cubic miles of ice underneath the surface of Mars. The plume, if it's there, may have heated the ice and turned it into liquid water. And the area where the plume is theorized to be just so happens to be where there is also evidence of the past presence of liquid water in Mars's surface.

"It’s very likely this plume is providing energy for liquid floods," said Broquet. "If there is indeed a plume it means the region is warmer than the rest of the planet. There could be pockets of liquid water there."

He's hesitant to put too fine a point on it, but he can't resist adding: "And life likes liquid water."

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