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Geoneutrinos—electron antineutrinos produced by radioactive decay inside Earth—offer an indirect way to study the planet’s hidden uranium and thorium and the heat those elements generate. Underground detectors measure candidate interactions; scientists then compare the signals with geological models to estimate where the antineutrinos came from. The resulting maps are model-based surface-flux predictions, not photographs of Earth’s interior or direct maps of water and other volatiles.
What are geoneutrinos?
Geoneutrinos are electron antineutrinos generated by radioactive decay within Earth. In the cited detector analyses, the principal sources are the decay chains of uranium-238 and thorium-232. Because antineutrinos can travel out from deep inside the planet, detectors can register evidence of those decays without sampling the material that produced them.
The detector does not identify a precise underground source for each event. It records candidate interactions, and researchers use energy distributions, backgrounds, detector exposure, and models of Earth’s composition to infer the geoneutrino contribution.
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How do geoneutrinos map Earth’s interior?
From detected events to an inferred signal
The first layer is the instrument: a detector records interactions consistent with antineutrinos and separates the geoneutrino signal from other events. The second layer is interpretation: scientists estimate how much of the signal should come from the crust and mantle using geological and geophysical models. That distinction matters because a detector measures events, not a three-dimensional image of the rocks beneath it.
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What a global flux map represents
The 2015 AGM2015 model combines vertically structured crust models and a mantle model to estimate energy-dependent antineutrino flux at Earth’s surface. It incorporates observational constraints from KamLAND in Japan and Borexino in Italy. The authors note that flux and spectrum predictions remain uncertain because the abundance and distribution of radioactive isotopes inside Earth are not fully known. AGM2015 is a scientific model, not a real-time or fully resolved map of the planet.
The interactive Geoneutrinos.org tool lets users explore modeled flux and signal for chosen uranium and thorium concentrations, including through a two-layer mantle solver. It is for exploring model assumptions, not an independent detector observation.
Why the crust matters
A detector’s signal includes contributions from both crust and mantle, and the crust near a detector can be especially important to estimating the mantle component. In the 2013 reference Earth model by Huang and colleagues, continental crust accounts for about 0.5% of bulk silicate Earth mass but contributes almost one third of its radiogenic heat power. A relatively thin layer therefore has an outsized role in interpreting what a detector sees.
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What have detectors measured?
Borexino’s 2020 result
In a 2020 analysis of 3,262.74 days of data collected from December 2007 through April 2019, the Borexino Collaboration reported a total geoneutrino signal of 47.0 TNU. The statistical uncertainty was +8.4/−7.7 TNU and the systematic uncertainty was +2.4/−1.9 TNU. TNU, or Terrestrial Neutrino Unit, is a conventional unit for reporting geoneutrino interaction rates.
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The mantle estimate required subtracting the expected lithosphere contribution, using detailed knowledge of the local crust. With that crust information, the analysis excluded the mantle-signal null hypothesis at 99.0% confidence. This is evidence for a mantle contribution under the analysis assumptions; it is not 99% certainty about one exact mantle composition.
What do geoneutrinos tell us about Earth’s heat?
Radioactive decay of uranium and thorium releases heat. Interpreting Borexino’s mantle signal, the 2020 paper estimated 24.6 +11.1/−10.4 terawatts of radiogenic heat from U and Th in the mantle. That figure is not total Earth heat: it is a model-dependent estimate for those elements in the mantle, not a direct, model-free measurement of all heat generated inside the planet.
The result illustrates both the value and the limitation of geoneutrinos. Antineutrinos can provide evidence about radioactive sources inaccessible to direct sampling, but turning event rates into an inventory or heat estimate depends on detector analysis and assumptions about the crust and mantle.
Can geoneutrinos reveal Earth’s missing potassium?
Not through the cited uranium-and-thorium maps. Uranium and thorium are refractory lithophile elements, while potassium is a volatile lithophile element. A 2026 article, “Probing Earth’s missing potassium using the antimatter signature of geoneutrinos,” describes a possible future approach to detecting potassium-40 geoneutrinos. Such a measurement could help investigate hidden potassium, radiogenic heat, and questions about Earth’s volatile-element inventory.
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That possibility is prospective, not an established potassium signal. Existing U/Th geoneutrino maps do not directly measure potassium or water, and they should not be read as maps of all volatile substances.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What comes next for geoneutrino observations?
China’s Jiangmen Underground Neutrino Observatory (JUNO) completed filling its 20,000-ton liquid-scintillator detector and began taking data on 26 August 2025. The Chinese Academy of Sciences lists geoneutrinos among the facility’s science targets, alongside reactor, solar, supernova, and atmospheric neutrinos. The announcement documents operations and planned capability; it does not report a JUNO geoneutrino discovery.
As more detector observations become available, they can test and refine models of radioactive-element distribution. The interpretation will still depend on how well researchers understand the crust around each detector and how they represent the deeper mantle.
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