Mars' Southern Half Is Weirdly Warm Underground. The 'Thermal Anomaly' Might Explain Why the Planet's Hemispheres Look So Different

Mars possesses a peculiar dichotomy between its northern and southern hemispheres. While the northern half exhibits low, flat terrain, the southern half features towering mountains and craters. Now, researchers believe they have uncovered yet another intriguing contrast, but this time beneath the planet's surface. A study published in Nature on August 26 reveals that the southern hemisphere's interior is significantly warmer, by hundreds of degrees, compared to the northern half.

This temperature anomaly could help explain several peculiar Martian phenomena and potentially provide insight into whether Mars ever had the conditions to support life. Much of our understanding of Mars' interior comes from NASA's InSight Lander, which gathered seismic wave data from 2018 to 2022. However, relying solely on one equatorial station led to assumptions that the interior was uniform globally.

To address this limitation, researchers used gravitational field variations to infer the planet's internal structure. By analyzing 16 years of data from three NASA spacecraft—Mars Global Surveyor, Mars Odyssey, and Mars Reconnaissance Orbiter—they developed a model revealing that the southern hemisphere is approximately 400 to 750 degrees Fahrenheit hotter than the northern half and partially molten.

Lead author Alexander Berne, a planetary scientist at the University of Arizona, expressed surprise at the consistency and precision of the findings, stating, "But maybe we shouldn't be surprised, because Mars seems to be dominated by these large-scale variations from north to south, so it makes sense that these variations also extend into the mantle."

The temperature asymmetry appears to mirror the north-south geographical boundary above the surface. This underground heat difference might account for other peculiar Martian features, such as magnetic anomalies in iron minerals found in the southern hemisphere. The interior thermal asymmetry could indicate a past magnetic field strong enough to generate distinct magnetic differences between the northern and southern hemispheres.

Additionally, seismic waves disperse more quickly in the south, potentially due to its higher temperature. The north-south heat difference is crucial for understanding processes that may have influenced Mars' hydrology, including the formation of basins that may have once held water. Mars' watery past is a key focus for scientists searching for signs of ancient life.

However, the reason behind this internal heat distribution remains a topic of debate. One hypothesis suggests that a colossal impact caused the northern hemisphere to release its heat. Another proposes that spontaneous upwelling brings heat from the core to the southern mantle. Alternatively, thick geological features in the south may be trapping heat, preventing its dispersal.

While the research sheds new light on Mars' internal structure, several questions remain unanswered. For instance, the location of Mars' largest volcanic province near the equator, rather than above the identified heat anomaly, is still puzzling. Moreover, the implications of this thermal anomaly for Mars' potential past plate tectonics are yet to be fully explored.