Since Earth’s surface is always being rearranged and its core is constantly being reshaped by the movement of tectonic plates, many people assumed that Mars had been a lifeless world for the previous three billion years.
Scientists from the University of Arizona question prevailing theories of Martian geodynamic development in the current edition of Nature Astronomy with a report on the finding of an active mantle plume pushing the surface higher and producing earthquakes and volcanic eruptions. The discovery suggests that the planet’s surface, which looks calm, may hide a more turbulent interior than was thought before.
This paper “presents multiple lines of evidence that reveal the presence of a giant active mantle plume on present-day Mars,” according to co-author Adrien Broquet.
Large chunks of heated, buoyant rock known as mantle plumes rise from the planet’s interior and push through the mantle, the planet’s intermediate layer, to the crust’s base. These plumes are responsible for earthquakes, faulting, and volcanic eruptions. Hawaii’s island chain, for instance, evolved when the Pacific plate slid slowly across a mantle plume.
According to Andrews-Hanna, there is compelling evidence that mantle plumes are “active on Earth and Venus, but this isn’t expected on a small and supposedly cold world like Mars.” Most scientists agree that Mars stopped being productive sometime between three and four billion years ago.
“A tremendous amount of volcanic activity early in the planet’s history built the tallest volcanoes in the solar system and blanketed most of the northern hemisphere in volcanic deposits,” Broquet adds. “What little activity has occurred in recent history is typically attributed to passive processes on a cooling planet.”
The researchers were surprised to find a lot of activity in an area of Mars called Elysium Planitia, which is a plain near the equator in the northern lowlands of Mars. Elysium Planitia has undergone significant eruptions over the last 200 million years, in contrast to other volcanic zones on Mars that haven’t seen significant activity in billions of years.
“Previous work by our group found evidence in Elysium Planitia for the youngest volcanic eruption known on Mars,” adds Andrews-Hanna. “It created a small explosion of volcanic ash around 53,000 years ago, which in geologic time is essentially yesterday.”
The Cerberus Fossae are a group of young cracks that run across the surface of Mars for more than 800 miles and are the source of the volcanoes in Elysium Planitia. NASA’s InSight team recently found that almost all quakes on Mars, called “marsquakes,” come from this one area. Even while records of recent volcanic and tectonic activity existed, their origin was still a mystery.
Volcanoes and earthquakes on Earth are usually caused by either mantle plumes or plate tectonics, which is the global cycle of drifting continents that recycles the crust over and over again.
“We know that Mars does not have plate tectonics, so we investigated whether the activity we see in the Cerberus Fossae region could be the result of a mantle plume,” Broquet adds.
Mantle plumes, which are akin to hot blobs of wax rising in lava lamps, reveal their existence on Earth via a predictable series of events. Warm plume material presses on the surface, causing the crust to rise and stretch. The plume’s molten rock then erupts as flood basalts, forming enormous volcanic plains.
When the team looked at the features of Elysium Planitia, they saw signs that the same thing happened on Mars. One of the highest places in Mars’ extensive northern plains, the surface has been raised by more than a mile. Analysis of small changes in the gravity field showed that this uplift is supported from deep within the planet, which is consistent with the presence of a mantle plume.
Other observations revealed that the floor of impact craters is inclined in the direction of the plume, providing more evidence for the theory that something pushed the surface up after the formation of the craters. When scientists used a tectonic model to examine the region, they concluded that the extension responsible for creating the Cerberus Fossae could only be explained by the existence of a huge plume at least 2,500 miles wide.
“In terms of what you expect to see with an active mantle plume, Elysium Planitia is checking all the right boxes,” says Broquet, adding that the finding poses a challenge for models used by planetary scientists to study the thermal evolution of planets. “This mantle plume has affected an area of Mars roughly equivalent to that of the continental United States. Future studies will have to find a way to account for a very large mantle plume that wasn’t expected to be there.
“We used to think that InSight landed in one of the most geologically boring regions on Mars – a nice flat surface that should be roughly representative of the planet’s lowlands,” Broquet adds. “Instead, our study demonstrates that InSight landed right on top of an active plume head.”
The existence of an active plume will impact interpretations of InSight’s seismic data, which must now account for the fact that this location on Mars is not typical.
“Having an active mantle plume on Mars today is a paradigm shift for our understanding of the planet’s geologic evolution,” Broquet adds, “similar to when analyses of seismic measurements recorded during the Apollo era demonstrated the moon’s core to be molten.”
The authors say that their findings could also be important for life on Mars. In the recent geologic past of the area being studied, there were floods of liquid water, but no one knows why. The same heat from the plume that keeps the volcanoes and earthquakes going could also melt the ice that causes floods and setting off chemical reactions that could keep life going deep underground.
“Microbes on Earth flourish in environments like this, and that could be true on Mars, as well,” says Andrews-Hanna, adding that the discovery goes beyond explaining the enigmatic seismic activity and resurgence in volcanic activity. “Knowing that there is an active giant mantle plume underneath the Martian surface raises important questions regarding how the planet has evolved over time. “We’re convinced that the future has more surprises in store.”
Image Credit: ESA/DLR/FU Berlin