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The Mystery of Mars’ One-Sided Magnetic Field

Just like Earth, Mars once boasted a powerful magnetic field that served to protect its atmosphere from the relentless solar wind. Today, however, only a remnant of that magnetic field lingers, leading to intriguing questions about the planet’s geological history and atmospheric evolution. Scientists have puzzled over why this magnetic signature is predominantly visible in the southern region of Mars.

Recent research from the University of Texas Institute for Geophysics (UTIG) sheds light on this anomaly, suggesting that Mars’ magnetic field may have been confined specifically to its southern hemisphere. According to Chi Yan, the lead author of the study and a research associate at the UT Jackson School of Geosciences, this discrepancy between the two hemispheres could explain the distinct magnetic imprint that we observe today. Unlike Earth, which has a magnetic field that encompasses the entire planet, Mars may have experienced a fundamentally different magnetic structure.

The research posits that this asymmetrical magnetic field could stem from Mars having a liquid inner core. Yan explained that if Mars lacks a solid inner core, it would be more feasible for the planet to generate a magnetic field that is lopsided. This characteristic could impact our understanding of Mars’ ancient dynamo—the process that generates its magnetic field—and imply significant insights on how long the planet could sustain its atmosphere.

Published in the journal Geophysical Research Letters, the study utilized advanced computer simulations to recreate this scenario. Previous investigations primarily relied on models that assumed Mars had a solid Earth-like inner core encased in molten iron. However, new findings from NASA’s InSight lander indicated that Mars’ core is composed of unexpectedly lighter elements, suggesting that it may be fully or partially molten.

If Mars currently possesses a molten core, it is likely that the core was also in a liquid state 4 billion years ago, during the time when the planet’s magnetic field was operational. To substantiate this hypothesis, the researchers conducted multiple simulations on supercomputers, gradually heating the northern part of Mars’ mantle compared to the southern area.

This differential heating created a dynamic where heat escaping from the core was concentrated at the southern hemisphere, generating sufficient energy to drive a dynamo effect and produce a robust magnetic field predominantly in that region. A planetary dynamo is a self-sustaining mechanism that results from movements within a molten core, which in turn generates a magnetic field.

According to Stanley, a co-author of the study and Bloomberg Distinguished Professor at Johns Hopkins University, the results of the simulations confirming a hemispheric magnetic field provide a new perspective on Mars’ internal structure, aligning well with the recent discoveries from InSight. This challenges established notions that asteroid impacts could have erased evidence of a potentially uniform magnetic field across the northern hemisphere.

As planetary researcher Doug Hemingway from UTIG notes, Mars offers an intriguing comparative study to Earth, particularly due to its similarities and differences that shape our understanding of planetary formation and evolution. Hemingway emphasized the importance of identifying what accounts for the stark contrast between the northern and southern hemispheres in terms of topography, terrain, and magnetic properties. Insights derived from this research can be invaluable in piecing together Mars’ complex geological narrative.

More information: C. Yan et al, Mars’ Hemispheric Magnetic Field From a Full‐Sphere Dynamo, Geophysical Research Letters (2025). DOI: 10.1029/2024GL113926

Source
phys.org