A technique to probe planetary interiors by measuring the attenuation of neutrino fluxes passing through the object.Neutrino tomography is a technique for imaging the interior of a planet or other large body by measuring how much a beam of neutrinos is absorbed as it passes through. Neutrinos are ghostly particles that interact so weakly with matter that they can traverse entire planets, but a tiny fraction are absorbed along the way. By placing detectors on opposite sides of an object and measuring the flux of neutrinos from a known source, scientists can infer the density distribution along the path, much like X-ray CT scans use absorption to map the human body.
The concept was first proposed in the 1970s, with early ideas by physicists such as A. De Rújula and others, but practical proposals for planetary imaging emerged in the 1990s and 2000s. No single inventor is universally credited, and the field remains largely theoretical, with experimental efforts still in early stages.
The method relies on the fact that neutrino absorption depends on the density and composition of the material they travel through. A powerful neutrino source, such as a particle accelerator or a natural source like the Sun, sends neutrinos toward a large detector on the far side of the target. By comparing the expected flux with the measured flux, and by using multiple paths at different angles, researchers can reconstruct a three-dimensional density map. The technique is challenging because neutrino interactions are rare, requiring enormous detectors and long exposure times, but it offers a unique window into otherwise inaccessible regions.
It is being explored for imaging the Earth's interior, particularly to detect hidden structures like magma chambers or to verify the composition of the core, and has also been suggested for scanning the interiors of other planets or moons.
Neutrino tomography could one day reveal whether the Earth's core contains a solid inner core or a more exotic state of matter, without ever drilling a hole.
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