Scientists find Mars’ core is more rocky road than smooth shortbread, revealing a messy birth past

In its early history, Mars suffered a massive collision that generated a global magma ocean and buried huge chunks of debris deep within the planet. (Image: Vadim Sadovski / Imperial College London)

Imagine biting into a Rocky Road brownie and finding uneven chunks inside. Scientists say the same is true for Mars’s interior, which still carries scars from violent events billions of years ago.

What did researchers discover about Mars’s mantle?
A study published in Science shows Mars’s mantle is uneven. Instead of smooth layers, it contains preserved fragments up to four kilometres wide. These pieces are remnants from the planet’s earliest days. NASA's InSight mission captured seismic shudders that uncovered such unseen structures. The research indicates Mars has preserved its turbulent history in the form of a geological time capsule.

Mars and the other rock planets were formed about 4.5 billion years ago. At that time, huge impacts molded their early surfaces. Scientists think planet-sized bodies impacted Mars with violent crashes. These crashes melted vast areas into vast magma oceans. When those oceans cooled, they sequestered chemically different chunks within the mantle. Unlike Earth, Mars never developed active tectonic recycling. Instead, a stagnant crust sealed its interior, preserving those ancient fragments.

What evidence supports this discovery?
InSight recorded eight clear marsquakes, including two from meteorite impacts. Seismic waves behaved differently when travelling through the mantle. High-frequency waves took longer to reach the sensors. Scientists linked this delay to interference from uneven fragments. The distribution resembled shattered glass, with large shards among many smaller ones. This pattern, researchers say, points to colossal early impacts.

On Earth, plate tectonics recycle crust and mantle continuously. Subduction zones pull surface material deep within, obliterating old traces. Mars does not have tectonic activity to stir its mantle. The result is a frozen record of its violent beginnings. Researchers say this preserved structure helps explain how stagnant worlds evolve.

Why does this matter for planetary science?
The discovery offers clues about rocky planets beyond Mars. It could reveal how Venus and Mercury developed over billions of years. Scientists believe these insights refine our understanding of planetary formation. Dr Mark Panning of NASA’s Jet Propulsion Laboratory said InSight’s data still shapes how researchers view rocky planets. Though the mission ended in 2022, its seismic record continues to produce fresh discoveries.