Mars May Have Hidden a Vast Magma System Despite Lacking Plate Tectonics

Researchers at the University of Oxford have found evidence that Mars may once have contained a vast, Earth-like magma system deep beneath its surface, even though the planet lacks the moving tectonic plates that drive similar processes on Earth. The findings, published in Nature Astronomy, suggest rocky planets can develop complex interiors without plate tectonics.

Mars is classified as a "stagnant lid" planet because its outer shell does not break into moving plates the way Earth's does. Scientists have long assumed this made its crust simpler than Earth's. To test that assumption, Oxford researchers examined seismic data from NASA's InSight lander, which placed the first seismometer on Mars in 2018 and recorded waves from meteoroid impacts and marsquakes — the Martian equivalent of earthquakes.

The team focused on a puzzling boundary about 24 kilometers below the surface that earlier studies had detected but not explained. By comparing the seismic readings with hundreds of possible rock compositions, they found that rock below the boundary was "ultramafic" (rich in iron and magnesium, low in silica), while rock above it was "mafic" (higher in silica). The researchers believe this layering formed when molten rock collected underground and separated over time, with dense crystals settling near the bottom while lighter, more processed melt rose upward — a process called transcrustal magmatism that was previously thought unique to Earth.

The buried layer could extend for hundreds, or even thousands, of kilometers across Mars's northern hemisphere, the study found. Lead author Dr. Tobermory Mackay-Champion, who worked on the research at Oxford's Department of Earth Sciences and is now at the University of Bristol, said the discovery suggests Mars could sustain "large, long-lived systems where molten rock evolved and reprocessed itself throughout the entire crust." The study was carried out by researchers from Oxford's Departments of Earth Sciences and Statistics, working with the University of Bristol.