Geoneutrinos are naturally produced electron antineutrinos from radioactive decay inside Earth. By counting a tiny number of them in large underground detectors, scientists can estimate how much heat uranium and thorium generate—and learn about the planet’s deep interior. They do not provide an underground picture: the measured signal mixes contributions from nearby crust and the mantle, and separating those sources depends on geological models.
What are geoneutrinos?
Geoneutrinos are electron antineutrinos created by natural radioactive decays in Earth’s rocks. They are not made by the detector. The most useful detected contributions come from the decay chains of uranium-238 and thorium-232. Potassium-40 also produces antineutrinos and contributes to Earth’s radiogenic heat, although its lower-energy antineutrinos are harder for many detectors to observe.
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These particles are extremely difficult to detect because they rarely interact with matter. A very large detector, operated underground for years, can nevertheless register a small number of interactions. The energy distribution and event rate of those interactions provide clues about radioactive material inside Earth.
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What can geoneutrinos reveal?
Radioactive heat from uranium and thorium
Radioactive decay releases heat. Measuring geoneutrinos gives researchers an independent way to constrain the heat generated by uranium and thorium, known as radiogenic power. It is one component of Earth’s heat loss; it is not the same as the planet’s total heat flowing outward, which also includes primordial heat left over from Earth’s formation and evolution.
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A detector reports a signal, not a heat value directly. Converting detected events into radiogenic power requires accounting for detector response, backgrounds, the distribution of radioactive elements, and the geological material between the source and detector. A count or signal rate therefore should not be read as a number of terawatts without that modeling step.
Clues about the mantle
Geoneutrinos reaching a detector come from both the crust and mantle. The crust near the detector can make a substantial contribution, so scientists estimate that local lithosphere signal using geological models and then constrain the mantle contribution. The resulting mantle estimate is not a direct measurement of a signal isolated from all other sources.
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Comparing measurements from detectors in different locations can help because the local crust differs from place to place. SNO+ describes the prospect of combining measurements from its Canadian detector with results from KamLAND and Borexino to infer uranium and thorium abundance in the deep mantle; that scientific rationale alone does not establish a newer combined result. SNO+ science programme
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The results below answer different questions: a detected signal, an inferred U/Th heat contribution, or a broader estimate that includes additional assumptions. They are not interchangeable measurements.
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| Study and quantity | Reported result | What it means |
|---|---|---|
| KamLAND, 2005: early detected geoneutrino count | Under an assumed thorium-to-uranium mass concentration ratio of 3.9, the 90% confidence interval was 4.5–54.2 events, compared with a model central value of 19; the paper set a 60 TW upper limit for U/Th radiogenic power. | An early measurement-era result, useful as historical context rather than a current central estimate. Nature report |
| KamLAND and Borexino, 2011: U/Th radiogenic heat | 20.0 +8.8/−8.6 TW | A combined U-238 and Th-232 contribution to Earth’s heat flux, with large uncertainty. KamLAND Collaboration paper |
| Borexino, 2020: measured signal | 47.0 TNU, with +18.3/−17.2% total precision; 52.6 geoneutrinos within a 68% interval. | Based on 3,262.74 days of data collected from December 2007 through April 2019. TNU is a signal-rate unit, not a heat-power unit. Borexino Collaboration paper |
| Borexino, 2020: total radiogenic heat estimate | 38.2 +13.6/−12.7 TW | Conditional on the study’s assumptions for mantle K-40 and lithospheric heat; it is not a model-free conversion of the measured U/Th signal. Borexino Collaboration paper |
| 2022 review: present-day radiogenic power | About 20 TW total, or about 16 TW from U and Th alone. | A combined-analysis and model-dependent estimate, not an exact universal value. Earth and Planetary Science Letters review |
The spread is not simply a contest between detector counts. In comparing results, it matters whether the value describes detected U/Th signal, inferred mantle signal, or total radiogenic heat; how local crust is modeled; whether potassium-40 is included; and how backgrounds and statistical and systematic uncertainties are treated.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What geoneutrinos cannot tell us
- They do not produce a detailed underground map. A detector measures rare interactions, not the direction and location of every radioactive decay. Geoneutrinos constrain models rather than furnishing an image of Earth’s interior.
- They do not directly measure total heat flow. U/Th geoneutrinos constrain one source of radiogenic heat; total surface heat loss also includes non-radiogenic contributions.
- U/Th measurements do not capture all radiogenic heat. Potassium-40 matters to the heat budget even where detector sensitivity to its antineutrinos is limited.
- A signal rate is not a heat estimate by itself. Translating an event rate into power requires assumptions about detector response, backgrounds, and the source distribution.
Why the heat estimate remains uncertain
Earth’s radioactive elements are not spread uniformly. The inferred signal depends on the local lithosphere model, the estimated crustal contribution, and what is assumed about material deeper in the planet. A detector’s location and the local crust composition therefore affect what it can say about the mantle. Statistical uncertainty from a small event sample is only part of the total uncertainty; geological and other systematic assumptions matter too.
For context, the 2011 KamLAND paper cited a contemporary total heat flux to space estimate of 44.2 ± 1.0 TW. That figure describes the estimate available to that study at the time, not a current global measurement or the radiogenic component alone. KamLAND Collaboration paper
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