Mars is squishy all the way down, less dense and more compressible throughout.
For the first time, seismic waves have passed through the heart of another planet and returned with answers. NASA's InSight lander, stationed on Mars for four years, captured tremors from two distant 2021 events that allowed scientists to peer directly into the Martian core—finding it wholly liquid, chemically complex, and unlike anything at Earth's center. This discovery reframes not only how Mars lost its magnetic field and its capacity for life, but how we might recognize the conditions for life elsewhere in the cosmos.
- Two violent 2021 events—a massive marsquake and a meteorite strike on Mars' far side—sent seismic waves cutting straight through the planet's core for the very first time.
- What scientists found disrupted existing models: Mars has no solid inner core whatsoever, just a single churning liquid mass of iron alloy dense with sulfur, oxygen, carbon, and hydrogen.
- This fully liquid, lighter-element-rich core likely explains why Mars lost its geodynamo billions of years ago—and with it, the magnetic shield that could have preserved its atmosphere and water.
- Researchers are now working to reconstruct the precise conditions that allowed hydrogen to settle into Mars' core, tracing the chain of events that turned a once-dynamic world barren.
- The findings sharpen humanity's ability to identify which distant exoplanets might sustain magnetic fields, atmospheres, and the conditions necessary for life.
For the first time, scientists have listened to the interior of Mars—and what they heard tells a story fundamentally different from our own planet's.
NASA's InSight lander spent four years recording hundreds of marsquakes from its fixed position on the Martian surface. The decisive moment came in 2021, when a giant marsquake and a meteorite impact on the planet's far side sent seismic waves traveling both around Mars and directly through its core. Like a sonic X-ray, those waves gave planetary scientist Jessica Irving of Bristol University and her team their first clear acoustic window into what lies at Mars' center.
The findings were striking. Mars' core is entirely liquid—a churning iron alloy carrying far more lighter elements than expected. Sulfur, oxygen, carbon, and hydrogen together account for roughly a fifth of the core's weight. Earth, by contrast, has a layered architecture: a liquid outer core surrounding a solid inner core, itself enclosing an even denser innermost region. Mars is fluid all the way down, less dense and more compressible throughout.
That distinction carries profound consequences. On Earth, heat rising from the solid inner core drives circulating currents in the liquid outer core, which the planet's rotation twists into the geodynamo—the engine behind our magnetic field. Mars lost that protection billions of years ago, leaving its atmosphere and water vulnerable to the solar wind. Scientists had long suspected that lighter elements in the core may have disrupted this process; now, for the first time, they have concrete data to test that idea. The presence of hydrogen in particular points to specific early conditions that shaped Mars' entire evolutionary path.
The implications reach beyond Mars. Understanding why two planets born from similar materials around the same star diverged so dramatically—one barren, one living—offers an essential guide for the search for habitable worlds. As the work published in the Proceedings of the National Academy of Sciences makes clear, the seismology techniques refined on Earth over more than a century have now opened a new chapter, one written in the tremors of another world.
For the first time, scientists have listened to the heartbeat of Mars—and what they heard tells a story fundamentally different from our own planet's interior.
NASA's InSight lander spent four years monitoring the red planet's seismic activity, detecting hundreds of marsquakes that rumbled through its depths. But the real breakthrough came in 2021, when two massive events—a giant marsquake and a meteorite impact—occurred on the far side of Mars from the lander. Because of their distance, these tremors sent seismic waves both around the planet and directly through its core, giving researchers their first acoustic window into what lies at Mars' center.
Using these waves like a kind of sonic X-ray, a team led by planetary scientist Jessica Irving of Bristol University mapped the Martian core's composition with unprecedented detail. What they found was striking: Mars' core is entirely liquid, a churning mass of iron alloy laced with surprising amounts of lighter elements. About a fifth of the core's weight consists of sulfur, oxygen, carbon, and hydrogen—a chemical signature radically different from Earth's architecture. Our planet has a layered core: a liquid outer shell surrounding a solid inner core, which itself wraps around an even denser innermost region. Mars, by contrast, is squishy all the way down, less dense and more compressible throughout.
This difference matters more than it might seem. Geologist Vedran Lekic of the University of Maryland notes that scientists have been using seismic waves to study planetary interiors since 1906, when earthquakes first revealed Earth's core structure. "More than a hundred years later, we're applying our knowledge of seismic waves to Mars," he says. "With InSight, we're finally discovering what's at the center of Mars and what makes Mars so similar yet distinct from Earth."
The composition of Mars' core holds clues to one of the planet's most defining mysteries: why it has no global magnetic field. On Earth, the magnetic field is generated by the geodynamo—heat rising from the inner core to the outer core creates circulating currents that, twisted by the planet's rotation, produce the field that shields our atmosphere and water from being stripped away by the solar wind. Mars lost this protection billions of years ago. Earlier simulations suggested that the presence of lighter elements in Mars' core could have disrupted this process, but now scientists have concrete data to work with. "There are small traces of hydrogen in Mars' core," Lekic explains. "That means there had to be certain conditions that allowed the hydrogen to be there, and we have to understand those conditions in order to understand how Mars evolved into the planet it is today."
The implications extend far beyond Mars itself. Understanding why two planets that formed from similar materials around the same star diverged so dramatically—one becoming a barren, airless world, the other a living one—offers a crucial lens for searching for habitable worlds beyond our solar system. As scientists scan distant exoplanets for signs of life, knowing which planetary interiors are most likely to sustain magnetic fields, atmospheres, and liquid water becomes essential. The work, published in the Proceedings of the National Academy of Sciences, represents a convergence of seismology techniques refined on Earth, mineral physics, and computational models of planetary evolution. It is, Irving notes, the payoff of a massive collaborative effort—and it has fundamentally changed what we know about the world beneath Mars' rust-colored surface.
Citações Notáveis
With InSight, we're finally discovering what's at the center of Mars and what makes Mars so similar yet distinct from Earth.— Vedran Lekic, geologist, University of Maryland
There are small traces of hydrogen in Mars' core. That means there had to be certain conditions that allowed the hydrogen to be there, and we have to understand those conditions in order to understand how Mars evolved into the planet it is today.— Vedran Lekic, geologist, University of Maryland
A Conversa do Hearth Outra perspectiva sobre a história
So we've known Mars was dead for a while—no magnetic field, no atmosphere to speak of. What does knowing the core's composition actually change?
It changes the story we tell about how it died. We can now ask: what conditions in that sulfur-rich, liquid core prevented the dynamo from working? That's not just trivia. It's the difference between understanding Mars as a static corpse and understanding it as a planet that evolved in a particular way.
The hydrogen traces seem oddly specific. Why does hydrogen matter so much?
Because hydrogen shouldn't be there under certain conditions. Its presence tells us something about the early Mars—about temperature, pressure, chemical reactions happening billions of years ago. It's like finding a fingerprint at a crime scene. It narrows down what could have happened.
Does this help us find life on other planets?
Directly, yes. If we're looking at an exoplanet and trying to guess whether it could support life, we now know to ask: does it have a liquid core with these lighter elements? Because if it does, it might lose its magnetic field like Mars did. That's a red flag.
So Earth's layered core is actually the unusual one?
In a sense, yes. Mars' all-liquid core is simpler, but Earth's complexity—that solid inner core—seems to be what keeps the dynamo running. We're still figuring out why. But now we have real data from another planet to compare against.
What happens next? Is InSight still listening?
InSight stopped transmitting in late 2022, so we have what we have. But this data will keep scientists busy for years. Every detail about that core composition feeds into models of planetary formation and evolution.