For decades, scientists have puzzled over the deep interior of Mars.
Did it resemble Earth, with a solid center wrapped in a liquid outer core, or was it entirely different because of the planet’s smaller size?
Now, thanks to NASA’s InSight mission, researchers have uncovered strong evidence that Mars has a solid inner core surrounded by liquid metal.
This finding, published in Nature, offers new insight into the red planet’s history and its transformation from a potentially habitable world into the cold, dry place we see today.
On Earth, the core is split into two layers: a solid inner sphere and a liquid outer shell.
Movements in the liquid layer generate Earth’s magnetic field, which shields our atmosphere from being stripped away by charged particles from the sun.
Without this invisible shield, Earth’s air and water would have been lost long ago.
Mars, however, does not have a global magnetic field today, raising questions about whether it once did—and if the loss of that field led to the thinning of its atmosphere and the disappearance of liquid water.
Clues from the Martian surface suggest that water once flowed in rivers, carved valleys, and filled lakes. Minerals that only form in water have also been found.
Combined with signs of past magnetization in the crust, this evidence points to a time when Mars may have been much more Earth-like, complete with a protective magnetic field.
The InSight lander, which operated on Mars from 2018 until 2022, carried a sensitive seismometer that listened to “Marsquakes.”
These quakes sent seismic waves rippling through the planet, bouncing and bending as they encountered different layers of rock and metal. By studying how these waves traveled, scientists could infer what lay deep inside.
Early studies showed that Mars had a liquid core, larger and less dense than expected, packed with lighter elements such as sulfur, carbon, and hydrogen. But the data was not strong enough to say whether a solid inner core existed.
That mystery has now been resolved. Using new analysis methods and carefully selected quake data, Huixing Bi of the University of Science and Technology of China and colleagues identified a solid inner core about 610 kilometers in radius.
This means Mars is undergoing crystallization as it cools—much like Earth. The discovery makes it more likely that Mars once generated a dynamo in its liquid core, which could have powered a magnetic field billions of years ago.
Far from sparking controversy, the new result builds on earlier studies and shows how science advances through better data and improved methods. As researchers continue to re-examine InSight’s recordings, the picture of Mars’ interior will become even clearer.
Ultimately, understanding how Mars’ core evolved will help answer a bigger question: what makes some planets habitable, while others lose their water and air to space?
