Martian mantle preserves shattered fragments from early planetary collisions

Martian mantle preserves shattered fragments from early planetary collisions
by Sophie Jenkins
London, UK (SPX) Sep 01, 2025

New seismic evidence suggests that Mars's interior is far from the smooth textbook image often imagined. Instead, the planet's mantle is littered with ancient fragments, some up to 4 km wide, formed during violent early collisions more than 4.5 billion years ago.

The study, based on seismic data collected by NASA's InSight lander, shows that seismic waves moving through Mars's mantle encountered interference consistent with a heterogeneous structure. Researchers liken the interior to a Rocky Road brownie, containing diverse chunks of material trapped when the young planet cooled.

Lead researcher Dr Constantinos Charalambous of Imperial College London explained that Mars was struck by giant objects shortly after its formation, generating vast magma oceans. As these cooled, they left behind chemically distinct chunks that remain preserved today. "These colossal impacts unleashed enough energy to melt large parts of the young planet into vast magma oceans," he said. "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."

Unlike Earth, where plate tectonics continually recycle the crust and mantle, Mars sealed over early beneath a stagnant lid, locking in its chaotic interior. This has preserved evidence of the planet's turbulent first 100 million years, offering scientists a rare glimpse of early planetary processes.

The seismic signatures came from eight clear marsquakes, including two triggered by meteorite impacts that left craters 150 metres wide. These quakes revealed a distribution of mantle fragments resembling a fractal pattern, with a few large shards surrounded by many smaller ones.

Professor Tom Pike, also of Imperial, compared it to a glass shattering on impact: "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."

The findings highlight how Mars differs from Earth and provide insights into how other rocky planets, such as Venus and Mercury, may have evolved. Dr Mark Panning of NASA's Jet Propulsion Laboratory noted: "InSight's data continues to reshape how we think about the formation of rocky planets, and Mars in particular. It's exciting to see scientists making new discoveries with the quakes we detected!"

Research Report:Seismic evidence for a highly heterogeneous Martian mantle