A rare active volcano on Mars may be causing the whole planet to spin faster
Scientists know Mars spins a little faster every yearbut the cause remains a mystery. Now, a new study published February 18 in the Geophysical Research Journal: Planets suggests that the reason may lie deep underground, where a huge plume of floating rock may be churning beneath the Red Planet’s crust.
This strange plume could help explain not only Mars’ faster rotation, but also how the planet retains geologic heat much longer than previously thought, forcing scientists to rethink how small, rocky worlds cool and die.
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Look beneath the surface
March to some of the the largest volcanoes and the mountains of the solar system. Indeed, unlike Earth, Mars does not seem to have plate tectonicsthe shifting crustal plates that drive much of our planet’s volcanic activity. Instead, lava from ancient active volcanoes on Mars sits there, accumulating and building much larger structures over time. This resulted in the formation of the Tharsis Volcanic Provincea region dotted with volcanoes that extends 3,700 miles (6,000 kilometers) through the surface of the planet.
In 2018, NASA sent the InSight lander to the Red Planet to better understand the planet’s interior, which could in turn help reveal more about its volcanoes. For years, the lander has studied Mars’ interior, giving scientists a direct estimate of the crust’s thickness.
Using data from InSight, Root and the team ran computer simulations to test what types of structures could explain why the volcanic region dominated one side of Mars. These models revealed a plume of unusually light material – called a “negative mass anomaly,” or something less dense than the rock surrounding it – in the mantle beneath the Tharsis region.
According to the researchers, this anomaly could explain why the Tharsis region became so large and so full of volcanoes.
“The negative or light mass anomaly will move upward and hit Mars’ lithosphere, introducing pockets of melt that may penetrate the crust and erupt as volcanoes,” Root said. (The lithosphere is a single rigid outer shell of approximately 310 miles (500 km) thick.
A solution for spinning?
The researchers then asked whether this same hidden plume of matter could also explain Mars’ strange rotation speed. Previous measurements comparing data from the Viking landers, which explored Mars in the 1970s, with data from InSight showed that the day on Mars is decreasing by about 70 microseconds per year. This means that the planet rotates slightly faster over time.
Root and his team used their simulations to calculate whether this less dense material beneath Tharsis could shift mass inside Mars enough to influence the planet’s rotation.
“With some simple calculations, we can explain the order of magnitude of the observed acceleration,” Root said. “Of course, more complicated modeling will be needed to better connect this.”
Root compared this process to someone spinning in an office chair while holding heavy books. If the books are pulled inwards, the spinning speeds up. Mars could do something similar with this less dense material.
“Negative mass flowing upward means something heavier must be coming down, and since the mass anomaly is located on Mars’ equator, that means the heavier mass is moving closer to [the] axis of rotation, therefore an acceleration,” Root said.
In addition to being a possible solution to some of Mars’ biggest mysteries, these models could help scientists better understand how rocky planets cool and eventually die. Mars is much smaller than Earth, so researchers have long assumed that it has lost its internal heat. relatively quickly. But if the Red Planet still has enough energy to cause deep mantle movement, it suggests that smaller worlds could remain active longer than expected.
“I would like to show that Mars is more interesting than we thought,” Root said.
Root, B., Qin, W., Van Der Tang, Y. and Thieulot, C. (2026). Describe the global gravity field of Mars with lithospheric flexure and deep mantle flow. Journal of Geophysical Research Planets, 131(2). https://doi.org/10.1029/2024je008765
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