It is no news for scientists that Mars has a distinct lack of a magnetic field. Many researchers think that’s a big reason why the planet lost most of its atmosphere. Without protection, the solar wind was free to sweep across Mars and carry much of its atmosphere away.
Recent findings continue to build the case that Mars once had a magnetic field. Measurements from the InSight lander support this view but reveal an unexpected detail. The magnetic field appeared concentrated in the southern hemisphere, with little to no presence in the north.
Researchers at the University of Texas Institute for Geophysics have put forward a possible explanation. In a new study, they suggest that a fully liquid core could have generated an uneven magnetic field. This revelation is in line with what InSight detected.
The structure of Earth’s core is more complex than early science lessons suggest. At the center lies a dense, solid inner core, surrounded by a layer of molten metal known as the outer core. The inner core remains solid because the pressure is high enough to keep iron and nickel locked in place. Movement within the outer core is what drives the magnetic field that extends across the planet.
Researchers once thought Mars had a core like Earth’s, with a solid inner core and a molten outer core that could produce a magnetic field. Around 3.9 billion years ago, this changed. Rocks from that time, like those in the Hellas and Isidis basins, should have become magnetized as they cooled. But they didn’t. This lack of magnetization suggests the magnetic field faded by then. The most likely explanation is that Mars’ core eventually solidified, halting the molten metal flow needed for a magnetic field.
Mars has an unusual feature in its magnetic field, i.e, a huge difference in strength between the northern and southern hemispheres. This strange contrast was first spotted during the Mars Global Surveyor mission in 1997, and later confirmed by data from the InSight lander. Scientists have suggested several reasons for this divide, from impacts by large asteroids to early tectonic activity in specific areas. Unfortunately, none of these explanations has been widely accepted in the scientific community.
On the bright side, Chi Yan and their team at the University of Texas have put forward a new theory. They suggest that Mars may have once had a fully molten core. Along with this, they believe that a dramatic temperature difference between the planet’s northern and southern hemispheres could have caused heat to escape mainly from the southern hemisphere.
A molten core on Mars could have been driving the planet’s magnetic field through a process called “planetary dynamo.” In contrast to Earth, where the solid inner core supports this process, Mars’ fluid core might have faced disruptions due to issues in the flow dynamics.
This theory may also clarify how heat was unevenly distributed. If the southern hemisphere had better thermal conductivity, it would allow heat to travel more easily through that region. As a result, the movements needed for the dynamo effect would primarily happen in the southern hemisphere.
To test their hypothesis, the researchers created a simulation of early Mars using advanced computing resources at the Maryland Advanced Research Computing Center. They altered the planet’s fluid dynamics and crust conductivity in the model. The closest match to data from InSight and Mars Global Surveyor came when Mars had a fully molten core, and there was a clear contrast in thermal conductivity between the northern and southern hemispheres.
There’s still much to uncover. The researchers recommend revisiting InSight’s seismic data to check if further evidence exists that aligns with the molten core theory. Future research could focus on enhancing simulations to incorporate a wider range of planetary variables or studying Martian meteorites from various regions and time frames.
Although this theory holds for now, there’s a long road ahead to fully prove its accuracy and explore its possible connections to the search for life on Mars.
References:
1 Mars’ Hemispheric Magnetic Field From a Full-Sphere Dynamo – C. Yan, A. Barik, et al. – Geophysical Research Letters – February 5, 2025 –