New research challenges the traditional understanding of Mars’s interior, suggesting a chunky texture, unlike the smooth and uniform depictions commonly found in textbooks, according to a new paper from scientists at Imperial College London.
The data analyzed for the new report came from NASA’s InSight mission, which captured anomalies in the Red Planet’s seismic vibrations that captured the researchers’ attention. What they discovered was surprising: 4-kilometer-wide chunks of rock in the Martian interior preserving the planet’s geological history.
A Violent Beginning
Roughly 4.5 billion years ago, the dust and rock orbiting our sun coalesced into rocky planets, including Mars. Following its formation, Mars was struck by a series of planet-sized objects that nearly destroyed the planet, in events similar to those that birthed Earth’s moon.
“These colossal impacts unleashed enough energy to melt large parts of the young planet into vast magma oceans,” said lead author Dr Constantinos Charalambous from the Department of Electrical and Electronic Engineering at Imperial College London. “As those magma oceans cooled and crystallised, they left behind compositionally distinct chunks of material – and we believe it’s these we’re now detecting deep inside Mars.”
Such violent events had a significant impact on the Red Planet, scattering and mixing pieces of the crust and mantle within the Red Planet’s molten interior, along with possible impact debris from the space rocks themselves. Because the mantle churned at such a slow rate, the mixing action was too weak to smooth the various pieces into an even texture as the planet cooled. These impact remnant chunks were then preserved, as Mars features a stagnant outer crust that sealed them inside, unlike Earth’s persistent and crushing plate tectonics.
“Most of this chaos likely unfolded in Mars’s first 100 million years,” says Dr Charalambous. “The fact that we can still detect its traces after four and a half billion years shows just how sluggishly Mars’s interior has been churning ever since.”
Mars Quakes Recorded
Among the bevy of data captured by NASA’s InSight lander, the team focused on eight particularly clear recordings of marsquakes. Intriguingly, two of those quakes were triggered by recent meteorite impacts, resulting in 150-meter-wide impact craters that now scar the Martian surface. How those impact sites interacted with seismic waves provided even greater detail about the Martian interior, as higher frequency waves took longer to journey from the crater to InSight, displaying signs of interference inconsistent with a smooth texture.
“These signals showed clear signs of interference as they travelled through Mars’s deep interior,” said Dr Charalambous. “That’s consistent with a mantle full of structures of different compositional origins – leftovers from Mars’s early days.”
“What happened on Mars is that, after those early events, the surface solidified into a stagnant lid,” he explained. “It sealed off the mantle beneath, locking in those ancient chaotic features — like a planetary time capsule.”
Mars Reveals Unexpected Features
The chunks discovered to hide in Mars’s mantle consisted of massive four-kilometer-wide pieces surrounded by many smaller pieces.
“What we are seeing is a ’fractal’ distribution, which happens when the energy from a cataclysmic collision overwhelms the strength of an object,” said co-author Professor Tom Pike. “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.”
Discovering Mars’s strange subsurface makeup may lead scientists to reconsider how other rocky planets in our solar system evolved, including Venus and Mercury. The peak at what lies beneath the Red Planet is a rare insight into one of our cosmic neighbors.
The paper, “Seismic Evidence for a Highly Heterogeneous Martian Mantle,” appeared in Science on August 28, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.