Scientists have long observed that Mars spins slightly faster each year, but the cause remained unknown. New research published February 18 in the Journal of Geophysical Research: Planets suggests a massive, buoyant plume of rock deep beneath the planet’s surface could be the culprit – and that this discovery challenges how we understand planetary cooling.
The Mystery of Martian Spin
For years, the subtle but measurable acceleration of Mars’ rotation puzzled researchers. While the planet’s surface appears geologically ancient, its interior dynamics are far from dead. The prevailing theory was that the planet was simply cooling at a slower rate than expected, but this new study proposes an active mechanism: a “negative mass anomaly” – a region of unusually light material – rising through the Martian mantle.
Why this matters: Planetary rotation isn’t just about speed; it reveals core processes. Understanding why Mars spins faster provides insights into its internal heat distribution, geological activity, and even its long-term habitability.
A Volcano-Shaped Anomaly
The study centers on the Tharsis volcanic province, a colossal region stretching 3,700 miles across the Martian surface. Unlike Earth, Mars lacks active plate tectonics. Instead, its volcanoes have grown over billions of years, piling up massive structures because lava accumulates in one place. NASA’s InSight lander, which studied the Martian interior from 2018, provided crucial data on crust thickness, which aided the research.
Researchers used computer simulations based on InSight’s findings to model the subsurface structure that could explain the Tharsis region’s dominance on one side of the planet. The models pointed to a plume of low-density material in the mantle beneath Tharsis.
“The negative or light mass anomaly will move upwards and hit the lithosphere of Mars, introducing melt pockets that have the potential to penetrate the crust and erupt as volcanoes,” explains Bart Root, the study’s lead author.
From Volcanoes to Velocity
The researchers theorize that this less-dense plume isn’t just fueling volcanic activity; it’s also influencing the planet’s spin. Measurements from the Viking landers in the 1970s and InSight show that Mars’ day is shrinking by roughly 70 microseconds per year, indicating a slight but consistent increase in rotational speed.
The team ran simulations to determine if the shifting mass from this subsurface plume could explain the observed acceleration. The results suggest that the lighter material rising towards the equator causes heavier mass to sink towards the rotation axis, speeding up the spin – similar to how a figure skater accelerates by pulling their arms inward.
Implications for Planetary Science
This discovery has broader implications. Mars is smaller than Earth, and scientists previously assumed it would cool and become geologically inactive relatively quickly. However, if a deep mantle plume can persist and drive volcanic activity, smaller rocky worlds may remain active for longer than previously thought.
This challenges the traditional view of planetary evolution: If Mars retains significant internal heat, it suggests other small planets and moons in our solar system and beyond could be more geologically dynamic than we realize.
The research is ongoing, but these findings could fundamentally change how we understand the interior processes of rocky planets. Further investigation will refine the models and provide more conclusive evidence, but for now, the hidden engine beneath Mars’ surface is reshaping our view of the Red Planet.
