Groundbreaking discoveries reveal a dynamic interior with a solid core, reshaping our understanding of planetary evolution
Imagine a world frozen in time, its deepest secrets preserved from the dawn of the solar system. While Earth's restless geology continuously recycles its surface through plate tectonics, Mars has maintained a geological record of its early formation virtually untouched for billions of years. This remarkable preservation makes the Red Planet an unparalleled window into the past—not just of Mars itself, but of all rocky planets, including Earth. Recent groundbreaking discoveries have begun to decipher this record, revealing a world with a surprisingly dynamic interior that continues to shape our understanding of planetary evolution and the potential for life beyond Earth.
Mars preserves a 4.5-billion-year geological record, largely undisturbed by tectonic activity
NASA's InSight lander provided the first detailed look at Mars' internal structure
For decades, Mars appeared to be a geologically dead world, especially when contrasted with our vibrant Earth. But looks can be deceiving. Thanks to NASA's InSight mission (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport), which landed on Mars in November 2018 and operated until December 2022, scientists have uncovered evidence of a far more complex planetary body. The mission's findings have revealed a planet with a lumpy mantle studded with ancient fragments, a liquid outer core, and most surprisingly—a solid inner core, fundamentally reshaping our understanding of the Red Planet's interior architecture 1 5 6 .
One of the most surprising early findings from InSight's data was the peculiar nature of Mars' mantle. Unlike Earth's mantle, which is continuously churned and mixed by the process of convection driven by plate tectonics, Mars' mantle has evolved sluggishly over billions of years, preserving structures from the planet's earliest history 1 .
Analysis of seismic waves passing through the mantle revealed that they were being slowed down and scrambled in ways that only made sense if the mantle contained small, localized regions of unusual material scattered throughout. Scientists determined that these anomalies represent giant lumps of rocky material—some as large as 2.5 miles across—that were delivered by massive impacts during Mars' infancy approximately 4.5 billion years ago 1 .
These impacts released cataclysmic energy that melted continent-sized swaths of the early crust and mantle, simultaneously injecting fragments of the impactors and Martian debris deep into the planet's interior. On Earth, such ancient structures would have been erased long ago by tectonic activity, but on Mars, they remain as planetary scars, offering clues about the violent processes that shaped the early solar system 1 .
| Layer | Discovery | Significance | Data Source |
|---|---|---|---|
| Crust | Thinner than expected, varying thickness | Reveals different evolutionary path from Earth | Seismic measurements |
| Mantle | Contains scattered "lumps" of ancient material | Preserves record of early impact history | Seismic wave anomalies |
| Outer Core | Liquid, rich in light elements (S, O, C, H) | Larger and less dense than previously thought | Seismic waves, free core nutation |
| Inner Core | Solid, approximately 613 km radius | Explains magnetic field history, core crystallization | PKKP and PKiKP seismic phases |
Perhaps the most groundbreaking discovery emerged from deeper within the planet. In 2025, analysis of InSight's seismic data provided definitive evidence that Mars possesses a solid inner core with a radius of approximately 613 kilometers (±67 km) 5 8 . This finding resolved a longstanding mystery about the Red Planet's internal structure and has profound implications for understanding its evolution.
The detection came from identifying two specific seismic phases in the data: PKKP (waves that transit through the core) and PKiKP (waves that reflect off the boundary between the inner and outer core). These signals revealed that Mars' core contains a distinct solid center with a compressional velocity jump of about 30% across the inner core boundary—a dramatic contrast that indicates a concentration of distinct light elements segregated from the outer core through crystallization processes 8 .
This discovery helps explain one of Mars' most significant mysteries: the history of its magnetic field. Evidence from Martian meteorites and orbital observations indicates that Mars once had a strong global magnetic field like Earth's, which disappeared approximately 4 billion years ago. Magnetic fields are generated by the motion of electrically conductive fluids in a planet's core—what scientists call a dynamo effect. The growth of a solid inner core releases heat and light elements into the liquid outer core, potentially helping to power such a dynamo 3 5 .
| Characteristic | Earth | Mars |
|---|---|---|
| Core Structure | Solid inner core, liquid outer core | Solid inner core, liquid outer core |
| Inner Core Radius | ~1,220 km | ~613 km |
| Inner Core/Planet Radius | 0.19 | 0.18 |
| Primary Core Elements | Iron-nickel with sulfur, oxygen | Iron-nickel with sulfur, oxygen, carbon, hydrogen |
| Magnetic Field | Strong global field | No global field (crustal remnants only) |
The confirmation of a solid inner core suggests that Mars may have once had an active dynamo driven by core crystallization, which would have generated the magnetic field that protected its early atmosphere. As the crystallization process slowed, the dynamo would have ceased, causing the magnetic field to collapse. Without this protective shield, the Martian atmosphere was gradually stripped away by solar wind, transforming Mars from a potentially habitable world with liquid water to the cold, dry planet we see today 5 .
The detection of Mars' inner core represents a triumph of experimental geophysics conducted at an interplanetary distance. The methodology employed by the research team showcases remarkable ingenuity in extracting subtle signals from complex data.
The analysis revealed a solid inner core with a radius of approximately 613 km, representing about 18% of the planet's total radius—remarkably similar to the proportion of Earth's inner core to our planet's radius (19%) 5 8 . The compressional velocity jump of around 30% across the inner core boundary indicates a significant difference in composition between the inner and outer core, likely resulting from the crystallization process concentrating certain elements while excluding others.
| Seismic Phase | Path | Role in Discovery |
|---|---|---|
| PKKP | Travels through mantle, reflects off core-mantle boundary, travels through core | Showed faster-than-expected travel times indicating high-velocity inner core |
| PKiKP | Travels through mantle and outer core, reflects off inner core boundary | Provided definitive evidence of solid inner core's existence |
| P'P'r_ab | Travels through core, reflects at surface, travels through core again | Helped constrain outer core properties |
| P'P'n | Similar path with different reflection point | Provided additional constraints on core structure |
This finding provides an anchor point for understanding Mars' thermal and chemical evolution. The presence of a growing inner core suggests that Mars is still undergoing gradual cooling and differentiation, albeit much more slowly than in its past. The relationship between inner core formation and the Martian magnetic field history offers crucial insights into dynamo generation across planetary bodies, potentially informing our understanding of magnetic fields on other worlds in our solar system and beyond 8 .
Unraveling Mars' internal secrets requires sophisticated technology and methods. Here are the key tools that enabled these discoveries:
A dome-shaped instrument placed directly on the Martian surface, SEIS was so sensitive it could detect ground movements of a billionth of a millimeter.
Protected SEIS from extreme temperature fluctuations and Martian winds that could generate noise masking genuine seismic signals.
Designed to burrow up to 5 meters into Mars' surface to measure heat coming from the planet's interior.
Measured the wobble of Mars' north pole as it orbits the Sun, providing information about the size and composition of the core.
Advanced computational methods that combined data from multiple marsquakes, creating a virtual seismic network from a single station.
Sophisticated statistical approaches that incorporate multiple lines of seismic evidence to produce probability-based estimates.
The discovery of Mars' inner core completes our picture of the Red Planet's internal structure and provides crucial insights into the evolution of rocky planets more broadly. Mars appears to represent an intermediate state between the completely solid cores of some planetary bodies and the vigorously active core dynamo of Earth. This positions Mars as a critical case study in planetary aging and the sequence of geological events that determine a world's fate 5 .
The findings also have profound implications for understanding Mars' potential habitability. The confirmation of a solid inner core supports the hypothesis that Mars once had an active dynamo generating a global magnetic field. This magnetic shield would have protected the early Martian atmosphere from solar wind erosion and allowed for more stable surface conditions, potentially including persistent liquid water—a key ingredient for life as we know it 5 .
"The geophysical implications relate to the geodynamics of Mars itself, its loss of its magnetic field, models of planetology compared to other planetary bodies... and also to the existence, even today, of a possible 'Martian geological vitality' in terms of the interaction between the outer and inner core, which could even be important for astrobiological purposes." — Jesús Martínez Frías, planetary geologist and astrobiologist 5
While Mars may appear geologically quiet on the surface, these discoveries reveal a world with continued internal activity—a planet that still holds heat and slowly evolves in its deepest interior. This "geological vitality" suggests that Mars may not be as dead as it appears, raising intriguing questions about what other surprises the Red Planet holds for future explorers.
Planet formation, differentiation into core, mantle, crust
Active magnetic field, warmer climate, liquid water
Magnetic field collapses, atmosphere stripped
Solid inner core detected, slow geological activity
As Antonio Molina, a planetary geologist specializing in Mars, observes: "One possible interpretation is that Mars is older than we thought (it has already begun the crystallization process of its interior and will be able to retain its internal heat for less time), but at the same time, the crystallization process may imply that Mars is 'more alive,' maintaining more efficient convection and therefore greater geological activity" 5 .
Future missions to Mars, including proposed sample return efforts that might one day bring Martian core materials to Earth for detailed study, will build upon these foundational discoveries. Each new piece of evidence helps refine our understanding of not just Mars, but of how all terrestrial planets form, evolve, and potentially become habitable—or lose that potential. The Red Planet's secret heart continues to beat, however faintly, and its rhythm tells a story that connects us all in the great cosmic saga of planetary evolution.