Mars once hosted vast, interconnected magmatic systems deep beneath its surface, despite lacking the plate tectonics long thought essential for such complexity, researchers from the University of Oxford have discovered. The findings, published in Nature Astronomy on 26 June, rely on seismic data from NASA’s InSight lander to map a mysterious boundary roughly 24 kilometres beneath the Martian surface.
That boundary separates silica-rich mafic rocks above from ultramafic material below—a 14-kilometre-thick layer of melt-depleted cumulate left behind as molten rock pooled, separated, and pushed lighter evolved melts upward. Statistical modelling assigns an 85.9 per cent probability to the mafic composition above and 90.8 per cent to the ultramafic below, with the planet’s petrologic Moho, where crust meets mantle, lying at about 38 kilometres. Dr. Tobermory Mackay-Champion, who led the study from Oxford’s Department of Earth Sciences before moving to the University of Bristol, said the scale of the hidden architecture overturns old assumptions. “We’ve traditionally assumed that volcanism on Mars was relatively simple compared to that on Earth. But this discovery suggests Mars could sustain large, long-lived systems where molten rock evolved and reprocessed itself throughout the entire crust,” he said.
The phenomenon, known as transcrustal magmatism, was once considered unique to Earth. The Oxford team’s thermodynamic modelling shows mantle upwelling and magmatic intrusion can drive the same crustal differentiation, even without moving plates. Professor Jon Wade, a co-author in Earth Sciences, said the result reaches well beyond the red planet. “If Mars could develop this kind of complex crust without plate tectonics, then maybe the conditions needed for habitability can emerge on more planets than we realised, including those previously dismissed based on size or their apparent lack of tectonic activity.”
InSight operated from November 2018 until December 2022 and gave scientists the first direct seismic readings from the Martian interior. Earlier studies had flagged a discontinuity at 20–24 kilometres, but its composition remained unclear. The Oxford group, working with colleagues in Statistics and the University of Bristol, ran hundreds of rock compositions through Bayesian classifiers to pin the boundary’s mineral make-up. The work accepted on 1 June adds weight to the idea that recycled water and volatiles—ingredients tied to life—may be more common across rocky worlds than past theories allowed.
About this article: This story was put together with the help of AI tools and checked by a real person on our team. We're a small crew trying to cover as much of the UK as we can on a limited budget. We're getting better every day - but we're not perfect yet. If something looks off, let us know. You're part of the process.
