By Satyabrat Borah
The red planet, Mars, has long captivated humanity with its rusty hues and tantalizing hints of ancient water and lost atmospheres. For centuries, we’ve gazed at it through telescopes, imagining vast canals or hidden civilizations, but only in recent decades have our robotic emissaries begun to peel back its secrets. Now, a groundbreaking study has delved deeper than ever before, revealing that beneath Mars’s dusty surface lies not a neatly layered interior like a pristine geological cake, but a chunky, heterogeneous mantle riddled with massive fragments of rock preserved from the planet’s tumultuous youth. This discovery paints a picture of a world born in violence, bombarded by colossal impacts that melted its surface into oceans of magma, only to cool into a stagnant, fossilized shell. The findings, drawn from seismic data collected by NASA’s InSight lander, offer a vivid snapshot of Mars’s early history and underscore just how different our neighboring planet is from Earth, while also shedding light on the chaotic processes that shaped rocky worlds across the solar system.
To understand this revelation, we must first consider the tools that made it possible. Launched in 2018, the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport, or InSight, mission was NASA’s first dedicated effort to probe the inner workings of another planet. Unlike rovers that roam the surface collecting rocks or searching for signs of ancient life, InSight was a stationary lander equipped with a highly sensitive seismometer designed to detect marsquakes, the Martian equivalent of earthquakes. Positioned in the Elysium Planitia region, a vast plain dotted with ancient volcanoes, the lander listened intently for vibrations rippling through the planet’s depths. Over its operational lifespan from 2018 to 2022, InSight recorded hundreds of seismic events, ranging from gentle tremors to more forceful shakes caused by meteorite impacts. These weren’t just random rumbles; they acted like acoustic probes, sending waves of energy through Mars’s crust, mantle, and core, where their speed, direction, and scattering patterns revealed the composition and structure hidden below.
The team behind the new analysis, led by planetary scientist and engineer Constantinos Charalambous from Imperial College London, focused on eight particularly clear seismic events. Two of these were especially dramatic: impacts from meteorites that gouged out craters about 150 meters wide on the surface. By meticulously studying how the seismic waves propagated from these sources, the researchers reconstructed a detailed map of the mantle, the thick layer of semi-solid rock sandwiched between the thin crust and the dense core. What they found defied expectations. Instead of a uniform, smoothly mixed mantle, Mars’s interior is peppered with enormous chunks of material, some stretching up to 4 kilometers across, surrounded by clusters of smaller fragments. These aren’t random debris; they are compositional relics, chemically distinct from the surrounding mantle, suggesting they originated from a time when the planet was still forming and highly volatile.
This chunkiness points to a history of extreme violence in Mars’s infancy, roughly 4.5 billion years ago, during the solar system’s formative Hadean-like eon. At that epoch, the young solar system was a cosmic shooting gallery, with protoplanets and asteroids hurtling through space and colliding with ferocious intensity. Mars, then a molten ball of rock about half the size of Earth, wasn’t spared. Massive impacts from planet-sized objects unleashed energies equivalent to billions of nuclear bombs, vaporizing surface material and excavating deep into the planet’s interior. “These colossal impacts unleashed enough energy to melt large parts of the young planet into vast magma oceans,” Charalambous explained in a statement accompanying the research. As these global magma seas cooled and crystallized over millions of years, they didn’t form a homogeneous slurry. Instead, the process left behind pockets of material with varying densities and compositions, including fragments of the original crust, mantle, and even debris from the impactors themselves. These chunks, like inclusions in a brownie, became embedded in the mantle as it solidified.
The pattern of these fragments is particularly telling. The seismic data revealed a fractal distribution: a few large shards accompanied by a multitude of smaller pieces, mirroring the way a glass shatters into big chunks and fine splinters when dropped on a hard floor. Professor Tom Pike, a co-author from Imperial College London, noted that this distribution arises when the energy of a cataclysmic collision overwhelms the structural integrity of the target. On Earth, such evidence would have been obliterated long ago by the relentless churn of plate tectonics, where crustal plates grind against each other, subducting old material into the mantle and recycling it through volcanic activity. But Mars evolved differently. Lacking Earth’s active plate boundaries, its crust formed as a single, rigid “stagnant lid” early in its history. This sealed the mantle below, trapping the ancient fragments in a sluggish, low-convection environment where they have drifted slowly ever since, preserved like geological amber.
This stagnant lid regime is key to understanding Mars’s overall evolution and why it contrasts so starkly with Earth. Earth’s dynamic tectonics not only recycles material but also generates a protective magnetic field through the motion of its molten outer core, shielding the surface from harmful solar radiation. Mars, however, lost its global magnetic field about 4 billion years ago, likely because its smaller size allowed it to cool faster, solidifying the outer parts of its core and halting the dynamo effect. Without this shield, solar wind stripped away much of the planet’s atmosphere over time, turning a once potentially habitable world into the cold, arid desert we see today. The chunky mantle reinforces this narrative of early vigor followed by dormancy. The preserved fragments indicate that while Mars experienced intense geological activity in its youth, including massive volcanism that built features like Olympus Mons, the largest volcano in the solar system, its interior has since become largely inactive. Seismic activity persists, with InSight detecting quakes up to magnitude 4.7, but these are far less frequent and powerful than Earth’s earthquakes, originating mostly from regions like Cerberus Fossae, a fracture zone possibly linked to lingering volcanic heat.
The implications of this discovery extend far beyond Mars itself. As the only other rocky planet we’ve seismically mapped in detail, Mars serves as a baseline for understanding the interiors of Venus and Mercury, our other inner neighbors, which remain enigmatic due to thick atmospheres or extreme temperatures that hinder surface probes. Venus, for instance, has a stagnant lid like Mars but shows signs of recent resurfacing through catastrophic volcanism, while Mercury’s tiny size suggests an even more rapid cooling history. By studying Mars’s preserved chaos, scientists can model how impacts influenced planetary differentiation, the process by which heavy metals sank to form cores while lighter silicates rose to create mantles and crusts. This has profound ramifications for habitability. The violent impacts that chunked up Mars’s mantle may have delivered water and organic compounds, essential for life, but they also boiled off atmospheres and sterilized surfaces. On Earth, the Moon-forming impact with a Mars-sized body called Theia similarly disrupted our planet, but plate tectonics and a sustained magnetic field allowed recovery and the nurturing of life.
These findings enhance our grasp of exoplanets, the thousands of worlds orbiting distant stars. Many detected exoplanets are rocky super-Earths, larger than Mars but smaller than giants like Neptune, and their formation likely involved similar bombardments. Knowing that such violence leaves detectable scars in the mantle could guide future missions to interpret seismic data from these alien worlds, helping assess their potential for life. Closer to home, the research bolsters NASA’s Artemis program and plans for human exploration of Mars in the 2030s. Understanding the planet’s interior aids in predicting seismic hazards for future bases and informs resource utilization, such as tapping into subsurface water ice or volcanic heat for energy.
InSight’s legacy, even after its panels succumbed to dust accumulation in 2022, continues to unfold through such analyses. The lander’s data has already confirmed Mars’s core is molten and smaller than previously thought, about 1,650 kilometers in radius, surrounded by a surprising low-velocity zone of partially molten rock. Now, with the mantle’s chunkiness added to the picture, we see Mars not as a dead world but as a dynamic archive of solar system history. As Charalambous and his team conclude, this “unprecedented window into the geological history and thermochemical evolution of a terrestrial planet under a stagnant lid” holds key implications for habitability across the cosmos. The red planet’s interior, far from being a boring uniform layer, is a testament to the universe’s raw power, a chunky relic of violence that reminds us how fragile and fierce planetary birth truly is. Future missions, perhaps including sample returns or advanced orbiters, will build on this, but for now, Mars has revealed its guts in startling detail, inviting us to ponder the shared origins of worlds both near and far.
