Neutrino Tomography of the Earth: Results from the IceCube Observatory ✛ ✦
Context
Understanding the internal structure of the Earth is fundamentally important for geophysics, because the mass distribution determines the geodynamo of the outer core, which generates the planet's magnetic field. Until now, the main tools have been seismic waves and gravitational measurements, which probe the macroscopic response of matter to elastic and gravitational forces. However, these methods leave uncertainties, especially regarding density in deep layers where no direct samples exist. Wolfgang Pauli—particles that interact exclusively through the weak interaction, predicted by Enrico Fermi—offer a fundamentally different probing method: their absorption in matter depends only on the traversed mass, allowing us to 'X-ray' the planet through. The IceCube collaboration's work uses this approach to obtain the Earth's density profile with unprecedented precision based on neutrino.
Methods
The IceCube detector, located at the South Pole, consists of a cubic kilometer of Antarctic ice instrumented with 5,160 digital optical modules that detect Cherenkov radiation—a vivid example of electromagnetism, described by Maxwell's equations, while the high speed of particles requires consideration of Lorentz transformations. For analysis, 368,071 muon tracks were selected, produced in interactions of muon neutrino with matter. Tracks are divided into starting and through-going. The energy and zenith angle of each event are reconstructed, and only upward-going events are used. Expected distributions are modeled using the Monte Carlo method within the framework of the Standard Model of particle physics, which includes a Quantum Field of weak interactions and the Higgs boson (Peter Higgs), giving mass to W and Z bosons. Parton distribution data from spectroscopy at the HERA collider are used. By varying the density in concentric shells, numerical simulation and Bayesian analysis are used to achieve the best match with observations.
Results
The radial density profile of the Earth was obtained for a five-shell model: inner core 0.60 (+0.60/−0.50) of 13 g/cm³, outer core (two layers) 0.72 and 1.1, mantle (two layers) 1.3 and 1.3 (normalized to PREM). The profile agrees with PREM within uncertainties. Earth's mass from neutrino: 7.25×10²⁴ kg (gravitational mass 5.97×10²⁴ kg lies below the 95% interval), which rules out the 'hollow Earth' hypothesis at a level greater than 5σ. Polar moment of inertia: 1.05×10³⁸ kg·m² with a reference value of 8.01×10³⁷ kg·m². Adding near-horizontal events improves accuracy for the outer shells.
Implications
For the first time, it has been shown that neutrino provides independent constraints on the Earth's mass distribution, using solely the weak interaction. This tests seismic models and opens the way to probing other planets. The inverse problem—using known density to measure the нейтрино interaction cross section—also becomes more accurate. Agreement with the Standard Model confirms particle physics in an energy range inaccessible to accelerators.
Future development
The next generation of telescopes (IceCube-Gen2, KM3NeT) will increase statistics by an order of magnitude and improve resolution, enabling transition to three-dimensional tomography. Refining neutrino and atmospheric flux models will reduce systematics. In the future, neutrino tomography may become a routine tool in planetary science, helping to peer inside Jupiter's moons.
Impact
The work will impact geophysics (refining interior models), particle physics (testing the Standard Model), astrophysics (understanding cosmic rays and their role in generating neutrino), and the development of large in-ice/underwater detectors.
Next steps
Next steps: data analysis with improved calibration from IceCube Upgrade and joint analyses with other telescopes. Detailed modeling of nuclear effects (shadowing, non-isoscalarity) is planned, along with incorporating muon flux data for direct measurement of atmospheric density.
Key open problems
The study touches on the problem of the Earth's core composition and dynamics (the nature of the geodynamo), as well as the precision of the neutrino interaction cross section at extreme energies, where deviations from the Standard Model are possible. It also contributes to understanding the acceleration of cosmic rays, which determine the flux of atmospheric нейтрино.
The knowledge machine's view
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What the work does
The study uses IceCube data for neutrino tomography of the Earth: by measuring the absorption of atmospheric muon neutrinos passing through the planet, the radial density profile is reconstructed within a five-shell model. The obtained estimates of mass and moment of inertia are consistent with the seismic model PREM and rule out the 'hollow' Earth hypothesis at a significance level greater than 5σ.
Where its strength is
The strength of the work lies in demonstrating a new independent method for probing the deep interior, based solely on the weak interaction, which allows testing geophysical models without relying on seismology or gravimetry.
Where it could go next
- It might be interesting to compare the obtained density constraints with results from neutrino tomography in other energy ranges or for other trajectories, as done in a recent review of the method.based on: Neutrino Tomography of Earth: A New Look at the Planet's Interior arXiv:2607.02644v2
- A related avenue is using neutrino telescopes to search for dark matter signals: a similar signal-background separation technique could help refine systematic uncertainties in your analysis.based on: Symphony of Shadows: Neutrino Telescopes Catch the Whisper of Dark Matter arXiv:2607.05335v1
- There is a paper in the archive about an underwater detector that also registers neutrinos passing through the Earth; comparing the sensitivities of different setups could suggest which regions of the planet become accessible as statistics accumulate.based on: An Underwater Hunter for Earth's Heat arXiv:2606.20780
Worth trying
- Try including near-horizon events with higher statistics in the analysis to improve resolution of the outer shells.
- Check how density constraints change when using alternative models of internal structure, such as a heterogeneous mantle.
- Assess which geodynamo parameters can be refined using the obtained moment of inertia as an additional constraint.
Why this may matter
Independent confirmation of the mass distribution in the Earth strengthens confidence in the standard geophysical model and opens the way to using neutrino tomography to study other planets or astrophysical objects where seismic methods are not applicable.
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Original abstract
as written by the authors arXiv:2607.02644
The Earth's interior reflects its geological evolution, from accretion to present-day dynamics. Its structure drives the geodynamo in the outer core, generating the magnetic field that shields the surface from charged cosmic radiation. The primary observables of the Earth's interior are its radial density distribution and derived quantities such as its mass and moment of inertia. These have traditionally been inferred from gravity and seismic wave propagation, which probe the macroscopic response of matter to gravitational and elastic forces. Here we instead constrain the Earth's density profile using high-energy neutrinos observed by the IceCube Neutrino Observatory at the South Pole. We analyze 10.7 years of predominantly muon-neutrino data spanning 500 GeV--100 TeV, including atmospheric neutrinos produced by cosmic-ray interactions in the Earth's atmosphere and the diffuse astrophysical neutrino flux. Neutrino attenuation depends on both the traversed column density and neutrino energy. By measuring the zenith- and energy-dependent flux suppression, we infer the Earth's radial density profile by fitting a concentric uniform-density shell model that incorporates neutrino fluxes, interaction cross sections, detector response, and glacial-ice systematic uncertainties. From the resulting density posteriors, we derive the Earth's mass and polar moment of inertia as measured by neutrinos. These are the most precise weak-interaction measurements of these quantities to date and are consistent with the Preliminary Reference Earth Model and independent gravitational determinations. Our results demonstrate that neutrinos provide a novel probe of planetary interiors via a distinct physical interaction, complementing gravity and seismology. With improved detectors and precision, neutrinos will further contribute to a multifaceted understanding of the Earth's structure.
The ice at the South Pole is so transparent that the Cherenkov light from a single neutrino can be detected by sensors hundreds of meters away. IceCube 'sees' neutrinos that have passed through the entire Earth, including the iron core, like an X-ray of the planet taken by ghostly particles.
In science fiction, neutrinos often act as ideal 'postmen' capable of penetrating any barriers — for example, for interstellar communication. This experiment turns fiction into reality, but with the reverse purpose: not to transmit information through the Earth, but to extract information about the Earth itself.
Key numbers
- data collection period: 10.7 years
- number of recorded tracks: 368,071
- neutrino energy range: 500 GeV – 100 TeV
- measured mass of Earth: 7.25×10²⁴ kg
- measured moment of inertia: 1.05×10³⁸ kg·m²