Deep beneath the Martian south, the planet is hiding a fiery secret. New gravity measurements show the interior there is 200 to 400 degrees Celsius hotter than the north, and it may be partially molten. The discovery, published in Nature on August 27, could unlock long-standing puzzles about Mars's magnetism, seismic activity, and ancient water.
A Gravity Map Reveals the Deep South's Secret
Researchers led by Caltech alumnus Alexander Berne, now at the University of Arizona, built a model that reads tiny gravity variations to see inside a planet. They applied it to Mars using decades of data from three missions: Mars Global Surveyor, Mars Odyssey, and Mars Reconnaissance Orbiter. By tracking minuscule changes in the spacecrafts' velocities, the team reconstructed the gravitational field around Mars.
The Sun's pull on Mars shifts with the seasons because the planet's orbit is slightly elliptical and its axis is tilted. The team used a method called tidal tomography to study how these gravitational signals change over time, creating a 3D model of the interior. Berne noted that scientists often assume planetary interiors are symmetric, but the new data shows Mars is not that simple.
A Hot South, a Cool North, and a Planet of Mysteries
Mars has always looked split: the south is covered in tall mountains and craters, while the north is mostly flat plains. Now it appears that split goes deep. The southern interior is hundreds of degrees warmer than the north, a hidden heat that could explain odd magnetic signals found in iron-rich rocks there. A hotter southern mantle might mean Mars once had a magnetic field strong enough to leave different magnetic imprints on each hemisphere.
The heat could also tie into findings from NASA's InSight mission, which previously detected seismic activity on the planet. The new model offers a fresh way to understand how Mars formed and evolved, including periods when it might have had conditions suitable for life.
For scientists, this is more than a curiosity. Understanding the interior structure of planetary bodies helps unravel the processes that shaped their formation and evolution. As Berne put it, these inferences give a blueprint for designing future missions and scientific exploration of these worlds. The Red Planet, it turns out, still has plenty of surprises buried deep below its surface.
