"These inferences in turn give us a blueprint for designing future missions and scientific exploration of these worlds," Berne says. "Understanding the interior structure of planetary bodies helps us unravel the processes that shaped their formation and evolution."

What does the thermal divide explain?

Scientists have known for decades that Mars looks strikingly different from north to south. The southern hemisphere is dominated by tall mountains and heavily cratered terrain. The north consists largely of broad, low-lying plains.

The new results suggest this contrast extends far below the surface — the planet is thermally uneven inside, with the southern interior hundreds of degrees hotter. That hidden heat could account for several puzzling observations:

• Unusual magnetism. Scientists have detected strange magnetic signatures in iron-rich minerals in the southern hemisphere. A hotter southern mantle could mean Mars once had a magnetic field strong enough to create magnetism differences between the two hemispheres.
• Seismic behavior. NASA's InSight mission previously found that seismic waves lose energy more quickly when passing through the south. Higher temperatures in that region could explain why.

Could the finding tell us about ancient water on Mars?

Potentially, yes.

"The dichotomy that we see between north and south is important to understand because it gives information about processes that may have influenced the hydrology of Mars, including the formation of basins that may have held water," says Amirhossein Bagheri, a postdoctoral scholar at Caltech and co-author on the paper. Bagheri is a former member of the InSight team.

Understanding the temperature difference could offer new clues about how Mars evolved, and how its landscape developed during periods when liquid water may have existed on the surface — including eras when the planet may have hosted environments capable of supporting life.

What caused the anomaly?

Researchers do not yet know, and the paper does not settle the question. Three hypotheses remain under consideration:

1. A giant impact released heat from the northern hemisphere.
2. Spontaneous convection — heat-driven churning — once occurred within the southern Martian mantle.
3. Thick geological structures in the south trapped heat and kept it from escaping efficiently.

All three possibilities remain preliminary explanations pending further study, and the gravity-based temperature estimates carry their own uncertainties inherent to modeling an interior no instrument can visit directly.

Who did the work?

The paper, titled "Tidal Tomography Reveals a Thermal Anomaly Beneath Mars's Crustal Dichotomy," includes co-authors from Brown University, the University of Arizona, NASA Goddard Space Flight Center, Academia Sinica in Taiwan, the University of Rome, Delft University of Technology, UCLA, the University of Texas at Austin, the University of Colorado Boulder, and UC Santa Cruz. NASA funded the research.

For now, the result offers a new view of Mars's interior: not a uniform ball of rock, but a planet with a deep, lopsided heat engine still shaping questions about its past.