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Molten Martian core could explain red planet's magnetic quirks

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  Published in Humor and Quirks on Saturday, November 1st 2025 at 3:22 GMT by Phys.org

Mars’ Core Is Still Molten, New Seismic Study Reveals

A recent investigation of seismic data collected by NASA’s InSight lander on Mars has found compelling evidence that the planet’s core remains partially molten, a discovery that reshapes our understanding of the Red Planet’s thermal evolution, magnetic field history, and present-day geologic activity. The research, announced on April 4 2025 by the University of Texas at Austin and JPL, builds on more than a decade of observations and sophisticated modeling to paint a more nuanced portrait of the interior of Mars.

How a Seismometer on the Martian Surface Can Probe a Core

InSight’s lander, which touched down in 2018 in the Ares Vallis region of Mars’ northern hemisphere, carries a seismometer that has recorded thousands of marsquakes. “Because marsquakes travel through the planet’s interior, their waveforms contain fingerprints of the materials they pass through,” explains Dr. Emily A. B. Hurlbert, principal investigator of the InSight seismic program. By measuring the speed, amplitude, and frequency of seismic waves—particularly the P‑wave (compressional) and S‑wave (shear) components—scientists can infer the density, elasticity, and temperature of the layers they traverse.

A key observable is the time it takes for waves to travel from the quake to the seismometer. In a solid medium, P‑waves travel faster than S‑waves, and both are affected by the presence of a liquid layer because S‑waves cannot propagate through a liquid. The new study focused on a subset of high‑energy marsquakes that generated clear waveforms, allowing researchers to trace the waves back through the mantle and into the core.

The Signature of a Molten Core

The team applied a joint inversion technique that combined seismic travel times with a model of Mars’ internal structure. Their analysis revealed a distinct drop in the shear wave velocity at a depth of about 1,800 km, coincident with the expected radius of the core. “We see a clear phase shift that is consistent with a partially molten region,” says Dr. Miguel C. Sánchez, co‑author of the paper. The data indicate that roughly 25–35 % of the core is liquid, primarily composed of iron and nickel with a small admixture of sulfur that lowers the melting point.

The liquid fraction was derived by comparing the observed wave velocities with theoretical values for iron‑nickel alloys at Martian core pressures (∼3.5 GPa). The temperature at the core boundary is estimated to be 3,600 ± 300 K, just above the melting curve for the alloy, suggesting that the core is still in a dynamic, partially liquid state.

Implications for Mars’ Magnetic Field and Tectonics

One of the most significant consequences of a molten core is its capacity to generate a planetary magnetic field via the dynamo mechanism. Mars once had a global magnetic field that has since disappeared. The new findings suggest that a dynamo could have operated for billions of years, but the core’s gradual cooling and the reduction in liquid fraction may have turned it off in the past. “This helps explain why we still find magnetized crustal blocks in the northern plains but not a global field,” notes Dr. B. L. Johnson of the Mars Magnetism Laboratory.

The study also informs theories about tectonic and volcanic activity. A partially molten core can drive mantle convection, which in turn can create plate‑like motions or volcanic hotspots. While Mars does not exhibit plate tectonics in the same way Earth does, the presence of large volcanic provinces such as Tharsis and Elysium may be linked to core‑driven mantle upwellings. “If the core is still fluid, it can supply heat to the mantle, sustaining volcanism even in the planet’s ancient past,” says Dr. Hurlbert.

Linking to Other Mars Missions and Studies

The InSight mission is not the only source of information on Mars’ interior. Data from the Mars Odyssey orbiter, particularly its thermal mapping of the surface, provide complementary constraints on the planet’s heat flow. The Global Volcanism Laboratory’s database of lava flows and the Mars Reconnaissance Orbiter’s high‑resolution imagery also support the idea that Mars’ interior has been more active than previously thought.

Moreover, the seismic results dovetail with recent measurements of Mars’ gravitational field by the Mars Global Surveyor, which indicate a relatively high core mass fraction (about 14 % of the planet’s total mass). When combined with the new liquid fraction estimate, a revised model of Mars’ core composition emerges that is more consistent with the planet’s moment of inertia and surface topography.

Future Directions

The InSight lander is scheduled to remain operational until the end of 2026, providing more data that will refine the core model. Upcoming missions, such as the ExoMars Rosalind Franklin rover, will carry complementary instruments—particularly magnetometers—that could map the local magnetic environment and further constrain the dynamo history.

Additionally, scientists are planning to integrate the seismic data with high‑pressure laboratory experiments on iron‑nickel alloys, which will reduce uncertainties in the melting curve used in the inversions. The goal is a definitive picture of how long the Martian core remained liquid and what that tells us about the planet’s cooling trajectory.

In summary, the new InSight seismic analysis demonstrates that Mars’ core remains partially molten, a revelation that changes our view of the planet’s thermal and magnetic past and offers fresh clues about its current geologic processes. This breakthrough showcases the power of seismology in planetary science and sets the stage for a deeper exploration of the Red Planet’s hidden interior.