Scientists analyzing 16 years of spacecraft tracking data have discovered a massive thermal anomaly deep beneath Mars, revealing that the mantle under the planet’s southern highlands is 200°C to 400°C hotter than the northern mantle. Published in the journal Nature, the research utilizes a novel method called tidal tomography to map deep interior structures, exposing a profound asymmetry that continues to shape the planet’s geology.
How Tidal Tomography Probed the Martian Interior
Instead of relying on seismic waves, researchers mapped the interior of Mars by tracking how the planet responds to seasonal mass redistribution. According to data collected from the Mars Global Surveyor, Mars Odyssey, and the Mars Reconnaissance Orbiter, carbon dioxide freezes onto one polar ice cap each winter and returns to the atmosphere before accumulating at the opposite pole.
That predictable shifting force deforms the planet’s interior. By monitoring tiny changes in the motion of the three orbiting spacecraft via radio tracking, scientists measured fluctuations in the Martian gravity field over a 16-year period. The time-varying gravity signal demonstrated that the mantle shear modulus—a measure of rock resistance to deformation—varies by more than 20% across the planet, with the most pronounced softness located beneath the southern highlands.
Interpreting Mantle Temperature and Composition
Temperature directly reduces the rigidity of mantle rock, but composition also plays a critical role in how the interior deforms. To explain the observed softness, the research team tested models that varied both internal heat and iron content.
The preferred scientific models indicate that the southern mantle requires approximately 200°C to 400°C of extra heat, alongside possible iron enrichment of up to 5%, to match the observed gravity data. Researchers emphasize that these elevated temperatures do not imply that the entire southern mantle is liquid. Warm rock can remain solid while flowing at extremely slow rates over geological timescales, and the measurements do not support the existence of a global magma ocean or a continuous molten layer.
Implications for Martian History and Surface Activity
The newly identified thermal contrast offers fresh clues regarding why Mars developed two distinct hemispheres: smooth northern lowlands contrasted against heavily cratered southern highlands. The asymmetry may stem from long-lived mantle upwelling, localized radioactive heating, insulation provided by a thick southern crust, or the lingering effects of ancient giant impacts.
While the warm mantle influences present-day volcanism, crustal stress, and subsurface ice stability, researchers stress that the thermal anomaly is not evidence of current volcanic eruptions, accessible liquid water, or life. Further investigation via extended spacecraft tracking will be required to refine models of the Martian interior.