When NASA’s InSight lander touched down on Mars in 2018, its primary job was to listen. The seismometer, borrowed from the French space agency CNES, was sensitive enough to detect ground motion smaller than the width of a hydrogen atom. Over four years of operation, it recorded hundreds of marsquakes and a steady drumbeat of meteorite impacts, each one sending seismic waves rippling through the planet’s interior.
Those waves carried information about the layers they passed through. And what they revealed, in data that scientists at the University of Oxford have only now fully analyzed, is that the subsurface plumbing of Mars is far more complex than anyone expected.
A boundary 24 kilometers down
The team focused on a seismic boundary roughly 24 kilometers beneath the Martian surface, a depth where the properties of the rock change abruptly. On Earth, such boundaries typically mark the transition between the crust and the mantle, or the base of a magma chamber. On Mars, the Oxford team concluded, this boundary was not the edge of an isolated pocket of molten rock. It was the signature of a lateral magma highway: molten rock that had pooled deep underground and spread sideways for long distances, connecting separate volcanic regions.
This contradicts the prevailing view of Martian volcanism. The planet hosts the largest volcanoes in the solar system, Olympus Mons, nearly three times the height of Everest, but the conventional model imagined them as isolated systems, each fed by its own independent magma source. The seismic data suggests something different: an interconnected plumbing network operating at a planetary scale.
Implications for the search for life
The discovery matters beyond geology. A planet with interconnected magma circulation can recycle elements between its interior and surface, creating chemical conditions that could support life, even without the plate tectonics that drives this recycling on Earth.
This widens the range of rocky planets that could be habitable. Previously, the assumption was that plate tectonics was necessary to maintain a stable climate and a geochemical cycle. Mars, lacking plate tectonics, was thought to be geologically dead. The Oxford team’s findings suggest that lateral magma transport can substitute for some of the functions of tectonics, keeping a planet’s chemistry active even when its crust does not move.
The analysis was based on data from InSight’s full mission, including seismic signals from impacts and quakes that penetrated deep enough to reveal the boundary. The lander was declared dead in December 2022 after dust accumulation on its solar panels cut power, but the data it sent back continues to yield discoveries about the planet’s internal structure.