Seismic signals from beneath the Martian surface have offered fresh insight into the planet's distant past, suggesting it once supported extensive magmatic networks that stretched from the lower crust to the surface. A study published in Nature Astronomy on 26 June 2026 presents evidence, drawn from NASA's InSight lander, of a melt-depleted lower crust and transcrustal magmatism on Mars.
The findings rest on seismic data recorded by InSight from marsquakes and meteoroid impacts. These recordings uncovered an intracrustal discontinuity roughly 24 kilometres beneath the surface. That boundary marks a shift from mafic rocks above to ultramafic rocks below, consistent with a roughly 14-kilometre-thick melt-depleted ultramafic cumulate zone in the lower crust.
Such a structure implies that Mars hosted vertically integrated transcrustal magmatic systems. These would have involved lower crustal melting, fractionation and upper-crustal magmatism, all without the need for plate tectonics. The discovery challenges earlier assumptions of relatively isolated magma chambers and instead supports the idea of large-scale, interconnected processes operating under a stagnant-lid regime.
Implications for planetary evolution
This more complex crust than previously thought carries wider consequences. It bears on questions of planetary habitability, the recycling of elements, the formation of atmospheres and oceans, and even the distribution of near-surface mineral resources. The work, led by the University of Oxford in collaboration with the University of Bristol, adds empirical weight to models of how rocky planets develop.
Key contributors from Oxford's Department of Earth Sciences include T. Mackay-Champion, J. Wade and J.-M. Kendall. Their analysis combined thermodynamic modelling and statistical techniques to interpret the seismic boundary, building a picture grounded in careful observation rather than speculation.
The InSight lander operated on Mars between 2018 and 2022, its seismometer capturing hundreds of events that allowed scientists to probe the interior. Earlier views of Martian volcanism often pictured simpler, disconnected reservoirs. The new data invites a revised understanding, one that sees conditions for intricate crustal evolution as potentially more common across the solar system, even absent the dynamic recycling provided by plate tectonics on Earth.