For centuries, Mars has fascinated humanity. Its red glow inspired myths, telescopes revealed shifting seasons, and rovers now crawl across its dusty deserts. Yet the greatest mysteries of the Red Planet are not found on its surface but buried deep within. New research published in Science has unveiled a startling truth: the interior of Mars is not neat and layered like a well-made dessert, but fractured, uneven, and chaotic—more like a Rocky Road brownie, riddled with chunks of its violent past.
This revelation, made possible by seismic data from NASA’s InSight mission, has given scientists a rare glimpse into the earliest days of planetary formation. Beneath the planet’s quiet exterior lies a geological time capsule—one that preserves evidence of cataclysmic collisions and magma oceans from billions of years ago.
The Myth of Smooth Interiors
In schoolbooks and popular illustrations, rocky planets like Earth and Mars are often shown as simple spheres with orderly layers: crust on the outside, mantle in the middle, and core at the center, stacked like the biscuit, caramel, and chocolate of a millionaire’s shortbread. It is an elegant picture—but it turns out that for Mars, reality is much messier.
The InSight mission, which landed on Mars in 2018 and operated until 2022, detected subtle anomalies in the way seismic waves traveled through the planet. These “marsquakes,” triggered both by natural tectonic activity and by meteorite impacts, revealed that the mantle is not uniform. Instead, it contains large, compositionally distinct fragments—some up to four kilometers across—left over from the planet’s earliest and most violent moments.
Born from Fire and Collision
Mars, like Earth, took shape about 4.5 billion years ago. In those first turbulent hundred million years of the solar system, newborn planets were bombarded by massive planet-sized objects. These colossal collisions unleashed staggering amounts of energy, melting much of the young Mars into vast oceans of magma.
“As those magma oceans cooled and crystallized, they left behind compositionally distinct chunks of material—and we believe it’s these we’re now detecting deep inside Mars,” explains Dr. Constantinos Charalambous of Imperial College London, the study’s lead researcher.
The chaos of early impacts mixed the crust, mantle, and perhaps even pieces of the colliding bodies themselves into the molten interior. But unlike Earth, which has remained geologically restless thanks to its system of shifting tectonic plates, Mars quickly froze into a stagnant state. Its outer shell hardened and sealed, locking these fragments inside. For billions of years, they remained undisturbed, silent witnesses to Mars’s primordial violence.
Listening to the Planet’s Pulse
The breakthrough came not from digging into Mars but from listening to it. InSight carried a highly sensitive seismometer that recorded the tremors of the planet. Eight especially clear marsquakes—including two triggered by fresh meteorite strikes—provided crucial data.
Seismic waves move differently depending on the materials they pass through. When scientists noticed that higher-frequency waves were slowed and scattered, it suggested the waves were colliding with irregular structures in the mantle. These were not smooth layers but interruptions—chunks of ancient rock, preserved like fossils within the planet’s body.
“What happened on Mars is that, after those early events, the surface solidified into a stagnant lid,” Dr. Charalambous explains. “It sealed off the mantle beneath, locking in those ancient chaotic features—like a planetary time capsule.”
A Shattered Interior
The fragments inside Mars are not randomly scattered but follow a recognizable pattern. Larger pieces are surrounded by many smaller ones—a “fractal” distribution that emerges when an object shatters violently.
Professor Tom Pike, a co-author of the study, compares it to everyday life: “You see the same effect when a glass falls onto a tiled floor as when a meteorite collides with a planet. It breaks into a few big shards and a large number of smaller pieces. It’s remarkable that we can still detect this distribution today.”
This shattering effect underscores the raw power of the early solar system. Mars did not simply accrete into a quiet world—it was battered, melted, and remade by forces so violent they left their mark billions of years later.
Mars and Earth: A Tale of Two Worlds
The contrast between Earth and Mars is profound. On Earth, plate tectonics continually recycle material between crust and mantle. Old seafloor is dragged beneath continents and melted, while fresh crust is born at mid-ocean ridges. This restless activity erases much of Earth’s earliest history, leaving geologists to piece together clues from scattered remnants.
Mars, however, took a different path. Its crust solidified early, and with no active tectonic system to churn its mantle, the planet became geologically stagnant. What scientists see inside Mars today is therefore not a dynamic, ever-changing system but a frozen relic. It is a record of events that occurred when the solar system itself was still young.
Implications for Other Planets
Mars’s fractured mantle is more than a Martian curiosity. It may hold lessons for how rocky planets evolve across the cosmos. Venus and Mercury, like Mars, lack Earth’s plate tectonics and may also preserve echoes of their violent beginnings within their interiors.
“InSight’s data continues to reshape how we think about the formation of rocky planets, and Mars in particular,” says Dr. Mark Panning of NASA’s Jet Propulsion Laboratory, which led the InSight mission. “It’s exciting to see scientists making new discoveries with the quakes we detected.”
By studying Mars, scientists may be able to reconstruct not only the story of one planet but also the shared history of all rocky worlds. The fractured interior of Mars could be a template for what lies beneath the surfaces of countless exoplanets orbiting distant stars.
A Time Capsule Beneath the Dust
For now, Mars sits quiet under its red deserts, its interior sealed beneath a stagnant crust. Yet its mantle tells a story more dramatic than any seen on its barren surface. It is a story of fire and impact, of worlds colliding and magma oceans boiling, of chaos frozen into stone.
Through the ears of InSight, humanity has caught whispers of that story. They are faint but profound, echoing across four and a half billion years to remind us that planets are not just spheres of rock but archives of cosmic violence and resilience.
Mars, in its silence, has preserved the memory of creation itself.
More information: Seismic evidence for a highly heterogeneous Martian mantle, Science (2025). DOI: 10.1126/science.adk4292
