Scientists say a plume of hot rock the width of the continental United States is rising from beneath the core of Mars and could help explain recent volcanism and earthquakes seen on the Red Planet.
Much of the volcanism on Mars occurred during the first 1.5 billion years of its history, leaving behind gigantic monuments such as Mount Olympus, the highest mountain in the solar system. However, scientists mostly believed that Mars has since cooled down, becoming practically dead over the last 3 billion years or so. But in recent years, scientists have noticed signs of geological activity, and now scientists have discovered a mushroom-shaped pillar of hot, floating rock under a region called Elysium Planitia that could explain the recent discoveries.
“Our study shows that Mars is not dead,” study lead author Adrian Brocke, a planetary scientist at the University of Arizona in Tucson, told Space.com.
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The story of the recent geology of Mars has begun to change with a 2021 study that found evidence that Mars may still be volcanically active, with evidence of an eruption within the last 53,000 years or so. Using data from satellites orbiting Mars, researchers have discovered previously unknown smooth, dark volcanic deposits covering an area slightly larger than Washington, DC. The deposits surround one of the fissures, forming a system of young fissures known as Cerberus Fossae. This region lies within the relatively featureless plains known as Elysium Planitia, located in the northern lowlands near the Martian equator.
In addition, NASA’s InSight lander has detected hundreds of quakes on the Red Planet, with most of these large quakes coming from Cerberus Fossae. In general, the results of the probe show that the level of seismic activity on Mars is between the lunar and the Earth.
In the new study, the scientists developed geophysical models based on geological, relief and gravity data from Elysium Planitia. They found evidence that this entire region is above a mantle plume, a column of hot rock rising from deep within Mars to set fire to overlying material like a blowtorch. Broquet said that this mantle plume formed about 930 miles (1,500 km) below the surface, at the boundary between the Martian core and the mantle layer, which itself rests between the Martian core and crust.
“We find that this giant plume is about the size of the continental United States, about 2,500 miles (4,000 km) — which is even bigger for a planet smaller than Earth,” Broke said.
Although this is the first mantle plume discovered by scientists on Mars, geologists have long known mantle plumes on Earth. For example, the island chain of Hawaii, formed as a result of the slow drift of the Pacific tectonic plate above the mantle plume.
The mantle plume material is buoyant compared to the surrounding rock. “It’s lighter, so it floats and migrates up, similar to what you might see in a lava lamp, where heated oil rises,” Broke said.
The researchers suggest that the center of the newly discovered Martian mantle plume is located exactly under Cerberus Fossae. They estimate that the plume is about 170 to 520 degrees Fahrenheit (95 to 285 degrees Celsius) hotter than its surroundings.
The researchers found that a mantle plume lifted the Martian crust more than 1 mile (1.6 km), bringing hot magma to the surface of the Red Planet and causing the Marsquakes detected by InSight.
“Not only is there young volcanism in the area, we are seeing that this volcanism is part of a recent resurgence in activity,” Broke said. “Until about 100 million years ago, the last major activity in this region was nearly 3 billion years ago. So, again, something had to happen to cause this volcanic revival, and that something is a mantle plume.”
Broquet said he suspects that Elysium Planitia was the only region on Mars with an active mantle plume, although a second plume may have lurked under Tharsis. He noted that Tarsis is a 3,000-mile (4,800 km) wide region near the equator in the western hemisphere of Mars that contains the largest volcanoes in the solar system and where scientists have detected recent and current volcanic activity.
However, according to him, volcanic activity on Tarshish can be explained not only by a mantle plume. For example, the earth’s crust is very thick and therefore can retain heat, helping to keep the rocks there in a molten state. On the contrary, “in the Elysium Planitia region, where we found the plume, the crust is known to be much thinner, and so we had to use another mechanism, that is, a plume, to cause volcanism,” he said.
The overlay shows the scale of the United States compared to Mars. (Image credit: NASA/JPL-Caltech)
active worlds
Overall, these data suggest that Mars is the third body in the inner solar system, after Earth and Venus, where mantle plumes are currently active.
“We used to think that InSight landed in one of the most geologically boring regions on Mars — a beautiful flat surface that should roughly represent the lowlands of the planet,” Brocke said. “Instead, our study shows that InSight landed right on top of the active plume.”
The new findings may also have implications for the search for life on Mars, the researchers said. The area where they found the plume also has the most recent evidence of liquid water flowing across the surface of the Red Planet. Because life is found almost anywhere there is water on Earth, scientists often focus their search for extraterrestrial life on areas where there is water.
“Water ice is thought to still be present in the interior of Mars, and so if the plume still provides warmth, which we think it does, pockets of liquid water or aquifers could be present near magma chambers in the Earth’s crust. Elysium Plains region,” Broke said. “On Earth, microbes thrive in such an environment. Therefore, I would say that the plume matters for the astrobiological potential of modern Mars. The next step could be to assess the presence of these aquifers and their possible location.”
It remains unclear how a mantle plume could have recently formed on a cooling Mars.
“A plume typically takes several hundred million years to rise from the core-mantle boundary to the surface,” Broquet said. “Once it reaches the surface, our Earth experience tells us that the plume remains active for a few tens to several hundred million years. Thus, from a geological point of view, this plume formed and reached the base of the earth’s crust relatively recently, which is surprising. This is not an old plume that survived the history of Mars.”
Broquet noted that scientists once thought the Moon was also geologically dead. “Because of its small size, it was expected to cool faster than the Earth,” he said. “However, seismic data recorded during the Apollo era was used to show that the core of the Moon is molten, which came as a big surprise. The moon is not cold and dead - it still has some warmth inside.”
Like these discoveries on the Moon, “our discovery is a paradigm shift in our understanding of how Mars evolved,” Broke said. “Such a large mantle plume is not predicted by the current model of the thermal evolution of Mars. Future research will need to use a new mechanism and a new geological history to find a way to explain the very large mantle plume that was not expected to occur. there.”
All in all, “there’s a lot of fundamental physics in the bowels of the planet that we obviously don’t understand,” Broke said. “Just like when we thought the moon was dead.”
The study is described in the article (will open in a new tab) published on Monday (December 5) in the journal Nature Astronomy.
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