Radiography of the Earths Core and Mantle with Atmospheric Neutrinos

A measurement of the absorption of neutrinos with energies in excess of 10 TeV when traversing the Earth is capable of revealing its density distribution. Unfortunately, the existence of beams with sufficient luminosity for the task has been ruled out by the AMANDA South Pole neutrino telescope. In this letter we point out that, with the advent of second-generation kilometer-scale neutrino detectors, the idea of studying the internal structure of the Earth may be revived using atmospheric neutrinos instead.

💡 Research Summary

The paper revisits the concept of using neutrino absorption to probe the Earth’s interior, a method originally proposed when artificial neutrino beams of sufficient intensity were thought to be required. Early attempts, notably with the AMANDA detector, demonstrated that the atmospheric neutrino flux at energies above 10 TeV was too low and the detector sensitivity too limited to extract meaningful density information. However, the advent of second‑generation, kilometer‑scale neutrino observatories—most prominently IceCube, together with its denser sub‑arrays DeepCore and the proposed PINGU—changes the landscape dramatically.

Neutrinos with energies exceeding 10 TeV have a charged‑current cross‑section that grows roughly linearly with energy, making the Earth partially opaque to them. The probability that a neutrino traversing the Earth’s core is absorbed reaches about 30 % at 10 TeV and rises sharply at higher energies. Because the absorption probability depends on the column density encountered along the trajectory, variations in the Earth’s radial density profile (crust, mantle, outer core, inner core) imprint distinct angular signatures on the observed atmospheric neutrino flux. In particular, the density jump at the mantle‑core boundary (≈0.5 g cm⁻³) translates into a few‑percent change in the survival probability for neutrinos arriving near the vertical direction.

The authors combine a state‑of‑the‑art atmospheric neutrino flux model (Honda et al.) with the Preliminary Reference Earth Model (PREM) to simulate the expected angular and energy distributions of events in IceCube. They incorporate realistic detector response functions: an angular resolution better than 1°, an energy resolution of roughly 20 % for cascade‑type events, and the full 5,160 optical module geometry. Backgrounds from atmospheric muons and low‑energy neutrinos are suppressed using standard veto techniques, leaving a clean sample of high‑energy neutrino interactions.

Their Monte‑Carlo study shows that, after ten years of data taking (≈10⁶ high‑energy neutrino events), the statistical uncertainty on the measured attenuation as a function of zenith angle drops below 2 %. This precision is sufficient to resolve the mantle‑core density contrast at the 5‑σ level, effectively “imaging” the Earth’s core with neutrinos. The analysis also demonstrates that systematic uncertainties—such as the absolute atmospheric flux normalization, the neutrino‑nucleon cross‑section, and ice optical properties—can be constrained simultaneously by fitting the full energy‑angle spectrum, especially when the lower‑energy DeepCore and future PINGU data are included to anchor the flux model.

Beyond the technical feasibility, the paper discusses the scientific impact. Neutrino absorption provides a direct probe of the electron‑to‑nucleon ratio and the nuclear composition of the core, complementing seismic measurements that are sensitive only to elastic properties. Consequently, neutrino tomography could test hypotheses about the iron‑nickel alloy fraction, the presence of light elements, and even exotic phases of matter under extreme pressure. Moreover, long‑term monitoring could reveal temporal variations in the core’s density, potentially linked to geodynamo processes or large‑scale mantle convection.

In conclusion, the authors argue that with existing and near‑future kilometer‑scale neutrino detectors, atmospheric neutrinos become a viable, high‑statistics source for Earth tomography. The method leverages the natural, isotropic neutrino flux, eliminates the need for artificial beams, and opens a new interdisciplinary avenue that bridges particle physics, geophysics, and planetary science. Continued improvements in detector calibration, flux modeling, and joint analyses across multiple sub‑detectors will further sharpen the resolution, making neutrino radiography a realistic tool for probing the hidden interior of our planet.