Molten core may hold key to Mars' uneven magnetic past

Mars once boasted a global magnetic field strong enough to protect its atmosphere, much like Earth's. Today, that shield is gone, and only remnants linger in the planet's crust-notably concentrated in the southern hemisphere. Scientists have long debated why this magnetic imprint is so one-sided.

The UTIG-led research suggests the answer may lie in Mars' interior composition. By simulating planetary magnetic behavior under early Martian conditions, the team found that if the Red Planet had a fully liquid core, it could have produced a dynamo that favored only the southern hemisphere. This contrasts with Earth's symmetric field, generated by a solid inner core surrounded by a liquid outer layer.

"The logic here is that with no solid inner core, it's much easier to produce hemispheric (one-sided) magnetic fields," said lead author Chi Yan, a UTIG research associate at the UT Jackson School of Geosciences. "That could have implications for Mars' ancient dynamo and possibly how long it was able to sustain an atmosphere."

The idea gained traction following NASA's InSight mission, which found Mars' core composition differed significantly from Earth's. According to co-author Sabine Stanley of Johns Hopkins University, the lighter elements detected suggest a lower melting point, making a molten core more likely both now and in Mars' distant past.

To explore this scenario, researchers ran computer simulations of early Mars, tweaking the mantle temperature between hemispheres to reflect natural asymmetries. They found that when the northern mantle was hotter, heat escape from the core was funneled more efficiently through the southern hemisphere. This created vigorous convection needed to power a hemispheric dynamo.

"We had no idea if it was going to explain the magnetic field, so it's exciting to see that we can create a (single) hemispheric magnetic field with an interior structure that matches what InSight told us Mars' interior is like today," Stanley said.

This theory provides a new perspective on a longstanding alternative: that asteroid impacts obliterated northern hemisphere magnetic signatures. Doug Hemingway, a planetary scientist at UTIG not involved in the study, finds the new model compelling.

"Mars is naturally interesting to look at because it's like Earth in some ways and it's the closest planet that we can imagine actually setting up shop on," Hemingway said. "But then, it's got this dramatic hemispheric dichotomy where the topography, the terrain and the magnetic field of the northern hemisphere and southern hemisphere are dramatically different. Anything that gives a clue at what could account for some of that asymmetry is valuable."

Research Report:Mars' Hemispheric Magnetic Field From a Full-Sphere Dynamo