By Daniel Stolte, University Communications
December 5, 2022
On Earth, shifting tectonic plates rearrange the planet’s surface and create a dynamic interior, so the absence of such processes on Mars led many to think of it as a dead planet, where not much happened in the last 3 thousand. millions of years.
In a study published In Nature Astronomy, scientists at the University of Arizona challenge current views on Martian geodynamic evolution with a report on the discovery of an active mantle plume pushing up on the surface, causing earthquakes and volcanic eruptions. The finding suggests that the planet’s deceptively calm surface may hide a more tumultuous interior than previously thought.
“Our study presents multiple lines of evidence that reveal the presence of a giant active mantle plume on present-day Mars,” he said. Adrien Mouthpiecepostdoctoral research associate at UArizona Lunar and Planetary Laboratory and co-author of the study with jeff andrews hannaassociate professor of planetary science at LPL.
Mantle plumes are large blobs of warm, floating rock that rise from the depths of a planet and through its middle layer, the mantle, to reach the base of its crust, causing earthquakes, fault lines, and volcanic eruptions. The Hawaiian island chain, for example, formed when the Pacific plate slowly moved over a mantle plume.
“We have strong evidence that mantle plumes are active on Earth and Venus, but this is not expected on a small, supposedly cold world like Mars,” Andrews-Hanna said. “Mars was most active 3 to 4 billion years ago, and the prevailing view is that the planet is essentially dead today.”
“A tremendous amount of volcanic activity early in the planet’s history built the highest volcanoes in the solar system and covered most of the northern hemisphere with volcanic deposits,” Broquet said. “The little activity that has occurred in recent history is generally attributed to passive processes on a cooling planet.”
The researchers were drawn to a surprising amount of activity in an otherwise nondescript region of Mars called Elysium Planitia, a plain within the northern lowlands of Mars near the equator. Unlike other volcanic regions on Mars, which have not experienced great activity for billions of years, Elysium Planitia experienced major eruptions in the last 200 million years.
“Previous work by our group found evidence on Elysium Planitia for the youngest known volcanic eruption on Mars,” Andrews-Hanna said. “It created a small explosion of volcanic ash about 53,000 years ago, which in geologic time is essentially yesterday.”
Volcanism on Elysium Planitia originates from the Cerberus Fossae, a set of young fissures that stretch more than 800 miles across the Martian surface. Recently, NASA’s InSight team discovered that almost all Martian earthquakes emanate from this region. Although this young volcanic and tectonic activity had been documented, the underlying cause remained unknown.
On Earth, volcanism and earthquakes tend to be associated with mantle plumes or plate tectonics, the global cycle of drifting continents that continually recycles crust.
“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 said.
Mantle feathers, which can be considered analogous to hot blobs of wax rising from lava lamps. give away his presence on Earth through a classic sequence of events. The warm material in the plume pushes against the surface, lifting and stretching the crust. Molten rock from the plume erupts as flood basalts creating vast volcanic plains.
When the team studied the features of Elysium Planitia, they found evidence of the same sequence of events on Mars. The surface has risen by more than a mile, making it one of the highest regions of the vast northern lowlands of Mars. Analyzes of subtle variations in the gravity field indicated that this uplift is sustained from deep within the planet, consistent with the presence of a mantle plume.
Other measurements showed that the floor of the impact craters is tilted in the direction of the spine, further supporting the idea that something pushed the surface up after the craters formed. Finally, when the researchers applied a tectonic model to the area, they found that the presence of a giant plume, 2,500 miles across, was the only way to explain the extent responsible for the formation of Cerberus Fossae.
“In terms of what you expect to see with an active mantle plume, Elysium Planitia is ticking all the right boxes,” Broquet said, adding that the finding poses a challenge for models used by planetary scientists to study the thermal evolution of the planets. “This mantle plume has affected an area of Mars roughly equal to that of the continental United States. Future studies will have to find a way to explain a very large mantle plume that was not expected to be there.
“We used to think that InSight landed on one of the dullest geologically regions of Mars, a nice flat surface that should be roughly representative of the planet’s lowlands,” Broquet added. “Instead, our study shows that InSight landed right on top of an active plume head.”
The presence of an active plume will affect interpretations of the seismic data recorded by InSight, which must now take into account the fact that this region is far from normal for Mars.
“Having an active mantle plume on Mars today is a paradigm shift for our understanding of the planet’s geological evolution,” Broquet said, “similar to when analyzes of seismic measurements recorded during the Apollo era showed that the core of the moon was cast”.
Their findings could also have implications for life on Mars, the authors say. The studied region experienced liquid water flooding in its recent geologic past, although the cause remains a mystery. The same heat from the plume that fuels ongoing volcanic and seismic activity could also melt ice to trigger flooding and spark chemical reactions that could support life deep underground.
“Microbes on Earth thrive in environments like this, and that could be true on Mars as well,” Andrews-Hanna said, adding that the discovery goes beyond explaining the enigmatic seismic activity and resurgence of volcanic activity. “Knowing that there is a giant mantle plume active below the Martian surface raises important questions about how the planet has evolved over time. We are convinced that the future holds more surprises in store.”