Mars has been viewed as a mostly geologically static world, but the planet may have an enormous underground plume of hot rocks slowly rising towards the surface
5 December 2022
A strange system of trenches on Mars may be hiding an enormous plume of hot rock rising from the planet’s core. This could upend our ideas of Mars as a mostly geologically static world and explain why so many marsquakes start near these fissures, which are known as Cerberus Fossae.
Mars doesn’t have plate tectonics, and after a long period of volcanic activity 3 billion to 4 billion years ago, things have largely been calm there. But recent studies, particularly measurements of marsquakes by NASA’s InSight lander, have indicated that something strange might be going on at Cerberus Fossae, which is in a region called Elysium Planitia.
Nearly all of the major quakes InSight has measured originated there, and it has felt a low, constant rumble of seismic activity that seems to come from nearby. Other observations have also suggested that the area might have been volcanically active just tens of thousands of years ago, far more recently than anywhere else on Mars.
Adrien Broquet and Jeffrey Andrews-Hanna at the University of Arizona hypothesised that this could all be explained by a phenomenon called a mantle plume, in which hot material from near the planet’s core begins to rise through the mantle of the planet, causing shaking and volcanic activity as it goes. “If you were to touch a mantle rock at its mantle temperature and pressure, it would definitively feel solid. But on a million years timescale, it will flow,” says Broquet.
If there is a mantle plume, it ought to press up on the ground atop it, creating a large hill and fracturing the ground. Cerberus Fossae has exactly those characteristics, and computer models of how the area would evolve over time with a mantle plume pressing upwards were an exact match. The models suggested that the plume measures more than 3500 kilometres across and is up to 285 degrees hotter than the surrounding area.
“This work provides an important crack in our understanding of Mars as a geodynamically dead planet,” says Sue Smrekar at NASA’s Jet Propulsion Laboratory in California. “It makes a compelling case for a stealthy but active mantle plume beneath Elysium Planitia.”
Not only would that explain why there are so many quakes there, it would also solve the long-standing mystery of how the strange landscape of Cerberus Fossae formed. “Having a mantle plume there is the only way to create the fissures that make up Cerberus Fossae,” says Broquet. “If not for this, the region should be in compression as the planet cools and shrinks.”
The heat from a plume would also melt some of the material above it, creating magma that may eventually seep out onto the surface. In fact, the seismic activity detected by InSight is probably related to magma rising through the ground, Broquet says.
That warmth could also be a boon for the potential of life on Mars. “The plume may also provide the heat to melt water underground, and I don’t want to be too optimistic, but on Earth this is an environment where microbes flourish,” says Broquet.
Journal reference: Nature Astronomy, DOI: 10.1038/s41550-022-01836-3
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