“Most of this chaos likely unfolded in Mars’s first 100 million years,” said Dr. Constantinos Charalambous of Imperial College London. The mayhem he speaks of is not figurative but real gigantic, planet-building impacts that devastated early Mars, reduced massive areas to magma seas, and deposited a thick interior crammed with boulders up to 4 kilometers wide.
These results, published in Science, are based on seismic data from 2018 to 2022 collected by NASA’s InSight lander. Analyzing eight beautifully resolved marsquakes, two caused by recent meteorite impacts that created 150-meter-wide craters, scientists found wave-interference patterns in the seismic waves small delays and scatter that betrays a mantle not uniform. “These signals showed clear signs of interference as they travelled through Mars’s deep interior,” Dr. Charalambous explained. “That’s consistent with a mantle full of structures of different compositional origins leftovers from Mars’s early days.”
Plate tectonics on Earth continuously recycles crust and mantle material through subduction and upwelling, erasing much of the Earth’s geological record of its earliest times. Mars, on the other hand, has a stagnant-lid tectonic regime, rigid, thick lithosphere encasing the mantle and isolating it from recycling by the surface. This immobility has allowed the disorganized debris to be entombed as a form of planetary time capsule for 4.5 billion years. The pattern in which these bits are distributed is fractal few large with many small ones around them all in keeping with the physics of catastrophic breakage when a meteorite strikes a planet or glass breaks on tile.
The discovery depended on an appreciation of the way seismic waves propagate through planetary interiors with multiple components. Where the mantle is strong, high frequencies travel well; in a “chunky” mantle, they become scattered, slowed down, and even destructively interfered with. It is such distortions that were used by the InSight team to image the depth and distribution of buried trash. This technique is similar to those used in Earth’s terrestrial seismology to investigate the transition zone of Earth in the mantle, but Mars provides a better picture because it is free from water-saturated crust and tectonic activity degrading deep seismic signals on Earth.
Complementary studies of Mars’ rheological structure its depth-dependent strength and deformation behavior help explain why these ancient features endured. Modeling shows that today’s Martian lithosphere is thick and strong, with brittle–ductile transition depths exceeding 100 kilometers in some regions under dry conditions, and maximum strengths surpassing 3,000 megapascals. In the wetter Noachian era, however, water-saturated minerals like phyllosilicates could have reduced frictional strength, potentially allowing more vigorous mantle convection and limited tectonic activity before the planet dried and locked into its stagnant-lid state.
Seismic studies also reflected a mid-mantle discontinuity at a depth of approximately 1,006 ± 40 kilometers due to post-olivine phase transition to high-pressure polymorphs wadsleyite and ringwoodite. The width of this boundary, 20 to 100 kilometers, implies that Mars’ mantle is iron-enriched relative to Earth’s. Geodynamically consistent with this discontinuity are models suggesting a modern mantle potential temperature of about 1,605 K and surface heat flux of 21 to 24 mW/m², values in agreement with slowly convecting interiors that can sustain heterogeneities for billions of years.
The implications are Mars-borne. Those same stagnant-lid planets, like Mercury and perhaps Venus, will be predicted to have their violent origins’ deep, unmixed reservoirs. By bridging seismic wave physics, mineral physics, and planetary rheology, InSight findings provide a new empirical standard against which rocky planet evolution models are tested. In the words of Dr. Mark Panning of the NASA Jet Propulsion Laboratory, “It’s exciting to see scientists making new discoveries with the quakes we detected!”
For planetary geologists, these pieces of crust, buried beneath the surface, are not just relics but documents of solar system early history, the memory of most recent giant impacts and magma ocean solidification. Every fragment is evidence, preserved by a tectonic regime which, unlike Earth’s, chose preservation over recycling.
