Led by Alexander Byrne, researchers analyzed two decades of NASA spacecraft tracking data to discover that the southern highland mantle is 200 to 400 degrees Celsius hotter than the north.
Deciphering the Martian Interior via Tidal Tomography
Direct thermal measurements of planetary cores remain impossible. Instead, the research team bypassed direct subsurface probing by turning to archival tracking data spanning nearly two decades from three distinct NASA orbiters: Mars Global Surveyor, Mars Odyssey, and the Mars Reconnaissance Orbiter.
To extract interior profiles from orbital mechanics, the team deployed an analytical framework known as tidal tomography. As Mars rotates, the varying gravitational pull of the Sun induces periodic tidal flexing across the planetary body. By monitoring minute shifts in the planet’s orbital speed and gravitational field induced by solar tides, the team mapped the mechanical response of deep-seated geological materials.
This methodology avoids invasive drilling or seismic deployment limitations, providing a robust technique for remote planetary profiling.
Quantifying the 400-Degree Thermal Divide
The resulting geophysical models expose a thermal and mechanical asymmetry that matches the planet’s well-documented crustal dichotomy. While the northern hemisphere consists of smooth, low-lying plains, the southern highlands feature heavily cratered terrain with a thicker crust.
The thermal discrepancy between the two hemispheres spans 200 to 400 degrees Celsius. This heat differential implies that the southern mantle is less rigid and potentially prone to partial melting.
Moreover, this thermal asymmetry provides a physical mechanism for anomalies detected by prior surface and orbital missions. Data gathered by NASA’s InSight lander previously highlighted variations in how seismic waves attenuate as they propagate through southern regions. A hotter southern mantle alters seismic wave dissipation profiles, creating a direct bridge between interior thermal states and surface-level seismology. Additionally, iron-rich rocks in the southern hemisphere retain signatures of an ancient magnetic field, which aligns with the distinct thermal and compositional boundaries revealed by the tidal tomography models.
Hypotheses Behind the Hemisphere Split
Planetary scientists continue to debate the root cause of this asymmetry. One hypothesis points to a catastrophic impact early in Martian history that delivered massive internal heat. Under this scenario, the impact energy or subsequent convective currents allowed the northern mantle to cool rapidly, or the thicker southern crust acted as an insulating thermal blanket that trapped heat beneath it.
Alternative hypotheses examine whether ancient mantle convection patterns or early geological processes concentrated thermal anomalies in the south. As Alexander Byrne noted regarding the broader implications of the work, these gravity-based analytical methods establish a blueprint for future planetary missions targeting Mercury or the large moons of Jupiter.
Decoding these deep interior profiles ultimately refines our understanding of the hydrologic history of Mars and the processes that contributed to the formation of basins that may have contained water in the past.
