Scientists have uncovered a dramatic temperature difference deep within Mars, with the planet's southern interior possibly hundreds of degrees hotter than its northern hemisphere. This discovery, based on gravity measurements and a technique called tidal tomography, suggests that the region beneath Mars's southern hemisphere is 200 to 400 degrees Celsius warmer than the north and might even be partially molten. The findings, published in the journal Nature on August 27, 2026, were led by Alexander Berne, a postdoctoral researcher at the University of Arizona and former Caltech alumnus. This thermal divide could reshape our understanding of Mars's internal structure and geological history. The research combined data from three major Mars missions: Mars Global Surveyor, Mars Odyssey, and Mars Reconnaissance Orbiter. By analyzing subtle changes in the spacecrafts' velocities, the team mapped Mars's gravitational field. The method used, known as tidal tomography, allows scientists to observe how gravitational signals change over time, offering a way to "see" into the planet's interior without direct drilling or sampling. This newly discovered thermal divide may help explain several long-standing mysteries about Mars. For example, it could clarify unusual magnetic patterns observed in the southern hemisphere and the behavior of seismic waves recorded by NASA’s InSight lander. Additionally, the findings might shed light on the planet’s ancient water history and the formation of large basins that may have once held liquid water. Understanding these features could provide clues about how Mars evolved over billions of years. While the cause of the thermal anomaly remains unclear, scientists have proposed several possibilities. One idea is that a massive impact event released heat in the northern region, while the southern hemisphere retained more warmth. Another theory suggests that natural convection within the southern mantle could be generating heat. There is also the possibility that thick geological layers in the south might act as insulators, trapping heat. The study, titled "Tidal Tomography Reveals a Thermal Anomaly Beneath Mars's Crustal Dichotomy," was conducted by researchers from multiple institutions, including Caltech, Brown University, the University of Arizona, and NASA Goddard Space Flight Center. The research was supported by NASA.