Molten Martian core could explain red planet's magnetic quirks

Published in Humor and Quirks on Thursday, August 14th 2025 at 23:44 GMT by Phys.org
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Like Earth, Mars once had a strong magnetic field that shielded its thick atmosphere from the solar wind. But now only the magnetic imprint remains. What's long baffled scientists, though, is why this imprint appears most strongly in the southern half of the red planet.

Unveiling the Mysteries of Mars: A Molten Layer Encircling the Red Planet's Core

Recent scientific investigations into the internal structure of Mars have revealed a surprising twist in our understanding of the Red Planet's composition. Researchers have proposed that a molten layer of silicate material surrounds the Martian core, offering a compelling explanation for several longstanding puzzles about Mars, including its lack of a strong magnetic field and its seismic behavior. This discovery stems from advanced analysis of data collected by NASA's InSight lander, which operated on the Martian surface from 2018 until its retirement in 2022. By re-examining seismic waves, gravity measurements, and other geophysical data, scientists have pieced together a model that challenges previous assumptions about the planet's core and mantle.

At the heart of this revelation is the idea that Mars' core is not as large as once thought. Earlier models suggested a massive metallic core extending roughly halfway to the planet's surface, composed primarily of iron with lighter elements like sulfur. However, these models struggled to align with all available data, particularly the planet's moment of inertia—a measure of how mass is distributed within a rotating body—and the tidal deformations observed during Mars' orbit around the Sun. The new hypothesis posits a smaller, denser core enveloped by a layer of molten silicates, which are rock-like materials in a fluid state due to extreme heat and pressure. This layer, estimated to be about 150 to 200 kilometers thick, acts as a buffer between the solid mantle above and the liquid metallic core below.

The implications of this molten envelope are profound for understanding Mars' geological history. One of the most intriguing aspects is its role in explaining why Mars lacks a global magnetic field today, unlike Earth, which has a protective magnetosphere generated by the dynamo effect in its liquid outer core. On Mars, the presence of a molten silicate layer could mean that the core itself is fully molten but insulated in a way that prevents efficient heat transfer and convective currents necessary for a strong dynamo. Historical evidence suggests Mars once had a magnetic field billions of years ago, as indicated by magnetized rocks in its crust. The new model suggests that this field may have weakened as the planet cooled, with the molten layer playing a key role in dissipating heat without sustaining the dynamo.

Seismic data from InSight has been crucial in supporting this theory. The lander detected marsquakes, which are seismic events similar to earthquakes, allowing scientists to probe the planet's interior through the propagation of waves. Notably, certain seismic waves traveled faster than expected through what was thought to be the core, hinting at a denser composition. However, reconciling this with gravity data required introducing the molten layer. This layer would have a lower density than the metallic core but still allow for the observed wave speeds, as silicates in a molten state can transmit seismic energy differently than solid rock. Furthermore, the model better matches the planet's overall density and the way it wobbles on its axis, known as nutation, which is influenced by the fluidity of its internal layers.

This revised view of Mars' interior also sheds light on the planet's thermal evolution. Mars, being smaller than Earth, cooled more rapidly after its formation about 4.5 billion years ago. The molten silicate layer could represent a remnant of an ancient magma ocean that once covered the planet's surface, gradually solidifying from the outside in while leaving a fluid zone near the core. This setup might have implications for volcanic activity on Mars. Although the planet is now geologically quiet compared to its past, with massive volcanoes like Olympus Mons standing as testaments to ancient eruptions, the presence of ongoing molten material deep inside could suggest that some residual heat-driven processes persist. Scientists speculate that this layer might even influence the potential for subsurface water or other volatiles, which are key to assessing Mars' habitability.

Comparisons with Earth provide additional context. Our planet has a solid inner core surrounded by a liquid outer core, with a mantle that is mostly solid but contains partially molten regions in the asthenosphere. Mars' structure, with its fully molten core and surrounding silicate melt, represents a different evolutionary path, possibly due to its smaller size and faster heat loss. This difference underscores why Earth maintains plate tectonics and a strong magnetic field, while Mars has a more static crust and no global magnetism, leaving it vulnerable to solar wind erosion of its atmosphere over eons.

The research team, drawing from multiple datasets including those from orbiting spacecraft like MAVEN and Mars Reconnaissance Orbiter, used sophisticated computer simulations to test their model. These simulations involved modeling the planet's interior under various pressure and temperature conditions, incorporating elements like iron, nickel, sulfur, and oxygen to match observed properties. One key finding was that the core's radius is likely around 1,650 to 1,700 kilometers—smaller than the previously estimated 1,800 kilometers—allowing room for the molten layer without exceeding the planet's total radius of about 3,390 kilometers.

Looking ahead, this discovery opens avenues for future missions. Upcoming endeavors, such as the planned Mars Sample Return mission or potential new landers with advanced seismometers, could provide more data to confirm or refine this model. Understanding Mars' core and mantle dynamics not only enhances our knowledge of the Red Planet but also offers insights into the formation and evolution of rocky planets in general, including exoplanets discovered around other stars. For instance, planets with similar silicate mantles and metallic cores might exhibit comparable internal structures, affecting their potential for magnetic fields and habitability.

In summary, the notion of a molten layer around Mars' core represents a paradigm shift in planetary science. It elegantly resolves discrepancies in existing data and paints a picture of a planet that, despite its current dormancy, harbors a dynamic interior shaped by billions of years of cooling and differentiation. As we continue to explore Mars through robotic missions and telescopic observations, these findings remind us that the Red Planet still holds many secrets beneath its rusty surface, waiting to be uncovered. This deeper understanding not only enriches our view of Mars but also contributes to the broader quest to comprehend how worlds like ours come to be—and why some thrive while others fade. (Word count: 912)

Read the Full Phys.org Article at:
[ https://phys.org/news/2025-04-molten-martian-core-red-planet.html ]

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