New seismic evidence reveals the Red Planet’s mantle preserves chaotic remnants of its violent beginnings

The inside of Mars isn’t the neatly layered structure often shown in textbooks. Instead, scientists have discovered a “chunky” interior — more like a Rocky Road brownie than the tidy layers of a Millionaire’s Shortbread.

Published in Science, the study shows that Mars’s mantle contains preserved fragments up to 4 km wide, dating back to the planet’s formation. These pieces act like geological fossils, offering clues to Mars’s early and violent history.

Traces of Gigantic Collisions

Mars, akin to Earth and other terrestrial planets, originated 4.5 billion years ago from the dust and rock surrounding the nascent Sun. However, its early history was influenced by monumental collisions with planet-sized entities – similar to those that presumably formed Earth’s Moon.

“These colossal impacts unleashed enough energy to melt large parts of the young planet into vast magma oceans,” explained lead researcher Dr. Constantinos Charalambous from 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.”

The impacts scattered fragments of crust, mantle, and possibly debris from colliding bodies into Mars’s molten interior. As the planet cooled, these fragments became ensnared in a slowly moving mantle, preserved like to ingredients included into a Rocky Road concoction.

A Planetary Time Capsule

Unlike Earth, Mars never developed plate tectonics to recycle its crust and mantle. Instead, it “sealed” early beneath a stagnant outer shell, preserving its interior as a geological time capsule.

“Most of this chaos likely unfolded in Mars’s first 100 million years,” said 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.”

Listening Deep With InSight

The evidence comes from seismic data collected by NASA’s InSight lander, which operated on Mars until 2022. Scientists studied eight clear marsquakes, including two triggered by meteorite impacts that left 150-metre-wide craters.

InSight’s seismometer detected seismic waves traveling through Mars’s mantle. Higher-frequency waves took longer to arrive at the sensors, revealing signs of interference. This pattern suggested a mantle filled with structures of mixed origin.

“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.”

Shards From Planetary Impacts

The fragments detected in Mars’s mantle appear in a fractal-like distribution: a few large pieces surrounded by many smaller ones.

Professor Tom Pike, co-author of the study, explained:
“What we are seeing is a ‘fractal’ distribution, which happens when the energy from a cataclysmic collision overwhelms the strength of an object. 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.”

Broader Implications for Planetary Science

These findings not only reshape our understanding of Mars but also offer insights into how other rocky planets like Venus and Mercury may have evolved.

“InSight’s data continues to reshape how we think about the formation of rocky planets, and Mars in particular,” said Dr. Mark Panning of NASA’s Jet Propulsion Laboratory in Southern California. “It’s exciting to see scientists making new discoveries with the quakes we detected!”

Summary of Key Findings

• The mantle of Mars contains intact chunks of up to 4 km in width, originating from its tumultuous early history.
• These fragments were formed by colossal collisions and magma oceans during the planet’s initial 100 million years.
• In contrast to Earth, Mars’s immobile crust has retained these internal formations as a planetary time capsule.
• Seismic data from NASA’s InSight mission indicated that the mantle is “chunky” rather than smooth.
• The fragments have a fractal distribution, like to shattered glass.
• The findings may elucidate the evolution of other terrestrial planets, including Venus and Mercury.

Original Publication
Authors: Constantinos Charalambous, W. Thomas Pike, Doyeon Kim, Henri Samuel, Benjamin Fernando, Carys Bill, Philippe Lognonné and W. Bruce Banerdt.
Journal: Science
DOI: 10.1126/science.adk4292
Article Title: Seismic evidence for a highly heterogeneous Martian mantle
Article Publication Date: 28-Aug-2025

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