Mars’s Mantle Holds Shocking Evidence of Catastrophic Impacts

New research published in the journal Science reveals that the red planet’s mantle preserves a record of its violent beginnings, shedding light on how Mars was shaped by cataclysmic impacts and early planetary processes.

Scientists say the discovery not only helps explain Mars’ geological evolution but also offers vital clues to understanding the history of rocky planets across the solar system.

Mars’ interior isn’t uniformly smooth like the pictures you see in textbooks. According to recent studies, it’s chunky rather than a neat slice of Millionaire’s Shortbread, more akin to a Rocky Road brownie.

The interiors of rocky planets like Earth and Mars are frequently pictured as smooth and layered, with the crust, mantle, and core stacked like the chocolate topping, caramel middle, and biscuit base of a millionaire’s shortbread. However, the situation on Mars is less neat.

Scientists from Imperial College London and other institutions discovered a messier reality after subtle anomalies were discovered in seismic vibrations picked up by NASA’s InSight mission: Ancient pieces up to 4 km wide from Mars’ formation can be found in its mantle; they are preserved like geological fossils from the planet’s violent early past.

About 4.5 billion years ago, dust and rock orbiting the young sun began to gradually clump together under gravity, giving rise to Mars and the other rocky planets.

After Mars had mostly formed, it was hit by massive, planet-sized objects in a series of near-cataclysmic collisions, the same type of collisions that probably created Earth’s moon.

Lead researcher Dr. Constantinos Charalambous from the Department of Electrical and Electronic Engineering at Imperial College London said, “These colossal impacts unleashed enough energy to melt large parts of the young planet into vast magma oceans.”

“As those magma oceans cooled and crystallized, they left behind compositionally distinct chunks of material—and we believe it’s these we’re now detecting deep inside Mars,” Dr. Charalambous added.

Fragments of the planet’s early crust and mantle, as well as perhaps debris from the impacting objects themselves, were scattered and mixed into the molten interior by these early impacts and their aftermath.

Like ingredients folded into a Rocky Road brownie mix, these chemically diverse chunks were trapped in a slowly churning mantle as Mars cooled, and the mixing was insufficient to completely smooth things out.

Mars sealed up early beneath a stagnant outer crust, preserving its interior as a geological time capsule, in contrast to Earth, where plate tectonics continuously recycles the crust and mantle.

“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.”

Seismic data from NASA’s InSight lander provides the proof, specifically eight particularly distinct earthquakes, two of which were caused by two recent meteorite impacts that left 150-meter-wide craters on the surface of Mars.

Scientists observed that waves with higher frequencies took longer to reach InSight’s sensors from the impact site because the instrument detects seismic waves moving through the mantle. They claim that these interference indicators reveal a chunky rather than smooth interior.

“These signals showed clear signs of interference as they traveled 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 further explained. “It sealed off the mantle beneath, locking in those ancient chaotic features—like a planetary time capsule.”

In contrast, at tectonic plates like the Cascadia subduction zone, where some of the plates forming the Pacific Ocean floor are pushed under the North American continental plate, the Earth’s crust is constantly gradually moving and recycling material from the surface into our planet’s mantle.

A few large fragments, up to 4 km wide, are surrounded by numerous smaller ones in a remarkable pattern of chunks found in Mars’ mantle.

Professor Tom Pike, who worked with Dr. Charalambous to unravel what caused these chunks, said, “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.”

Our knowledge of the evolution of other rocky planets, such as Venus and Mercury, over billions of years may be affected by this discovery. A unique window into what might be concealed beneath the surface of dormant worlds is provided by this recent discovery of Mars’ preserved interior.