Mars's Southern Hemisphere Mantle Is 200–400°C Hotter Than the North Underground, Based on 16 Years of Gravity Data from Three Spacecraft

Explanation

On Mars, the northern hemisphere is low and smooth, while the southern hemisphere is high and rugged. Why this "crustal dichotomy" arose has long been unknown.

A team led by Alexander Berne of the University of Arizona used a method to measure the internal temperature of Mars without sending a spacecraft to Mars. Because Mars orbits the Sun in an elliptical path, the tidal force it receives from the Sun changes periodically. The slight deformation of Mars caused by this force appears as deviations in the orbits of orbiting spacecraft. The team analyzed 16 years of radio tracking data from three NASA orbiters (Mars Global Surveyor, Mars Odyssey, and Mars Reconnaissance Orbiter) and found that the stiffness of the mantle (shear modulus) differs by more than 20% between north and south. Since stiffness is determined by temperature, converting this to temperature shows that the southern hemisphere's mantle is about 200–400°C hotter than the north's.

Part of the southern hemisphere's mantle may be molten. However, seismic data from the InSight lander suggest it is unlikely that the entire mantle is widely molten.

Why only the south is hot remains unknown. There are three hypotheses: a giant impact on the northern hemisphere released heat, convection occurred in the southern hemisphere's mantle, or the southern hemisphere's thick crust trapped heat — and all three could explain this result.

The paper was published in the scientific journal Nature on August 27, 2026.