A Tale of Two Hemispheres
Mars hides a massive thermal secret beneath its southern highlands. Research published on August 27 in Nature reveals a thermal anomaly that leaves the Red Planet's southern mantle between 390 and 750 degrees Fahrenheit warmer than the north. This temperature gap suggests the interior is far from the uniform sphere many models once assumed.
Alexander Berne of the University of Arizona led the study. He analyzed archival data from three NASA missions: Mars Global Surveyor, Mars Odyssey, and the Mars Reconnaissance Orbiter. By tracking subtle shifts in orbital velocity, the team identified variations in the planet's gravitational field that correspond to this hidden heat. The southern mantle is so warm that parts of it might remain molten today.
Rethinking Planetary Structure
This discovery forces a hard look at the Martian dichotomy. The northern hemisphere consists of flat lowlands, while the south features a thicker, cratered crust. That southern crust sits an average of 15.5 miles deeper than its northern counterpart. Such asymmetry hints at a violent history.
One explanation involves a massive impact four billion years ago. If a giant object struck the north, it could have gouged out a basin while accelerating the cooling process for the northern mantle. Another theory argues the thick southern crust acted as an insulating lid, trapping heat inside the planet for billions of years.
Solving Old Mysteries
Existing data from the InSight lander now makes more sense. When the lander's seismometer recorded seismic waves, they dissipated faster in the south than expected. This rapid loss of energy is a predictable result of the higher temperatures found in this new study. It confirms the thermal anomaly is physically present.
Magnetic signatures in the planet's iron-bearing minerals also find a logical home in these findings. Mars lost its global magnetic field long ago, yet magnetic remnants persist in southern minerals. The extreme heat from the southern mantle may have crossed the Curie temperature, erasing older magnetism and resetting the magnetic signature of the region.
Expanding the Technique
Berne developed a method called tidal tomography to perform this analysis. It accounts for the sun's gravitational pull as Mars moves along its elliptical path. The technique provides a three-dimensional view of interior structures that was previously impossible to obtain without landing on the surface.
Researchers expect this approach will work for other celestial bodies. Mercury, along with the large moons orbiting Jupiter, are primary candidates for future study. The findings represent a blueprint for how scientists might interpret gravity data to map out the hidden interiors of worlds across the solar system.