Neutrino Tomography of the Earth: Results from the IceCube Observatory ✦
Based on 10.7 years of muon neutrino observations (energies from 500 GeV to 100 TeV) with the IceCube detector at the South Pole, the suppression of the neutrino flux as a function of zenith angle and energy—caused by absorption during passage through Earth—has been measured. Neutrino attenuation depends on the product of path length, density, and energy, allowing the radial density distribution in the interior to be reconstructed. A model of concentric shells with constant density was applied, incorporating neutrino flux parameters, interaction cross-sections, detector response, and systematic uncertainties from the glacial ice. From the posterior density distributions, Earth's mass and polar moment of inertia were derived. These are the most precise measurements of these quantities to date using the weak interaction; they agree with the Preliminary Reference Earth Model (PREM) and independent gravitational data. The results demonstrate that neutrinos open a new avenue for exploring planetary interiors, complementing seismology and gravimetry.
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. Нейтрино—particles that interact exclusively through the weak interaction, predicted by Ферми—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 слабого взаимодействия.
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 электромагнитного излучения, described by уравнениями Максвелла, while the high speed of particles requires consideration of преобразований Лоренца. For analysis, 368,071 muon tracks were selected, produced in interactions of muon нейтрино 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 стандартной модели of particle physics, which includes a квантово-полевое описание of weak interactions and the хиггсовский механизм (Хиггс), giving mass to W and Z bosons. Parton distribution data from спектроскопии at the HERA collider are used. By varying the density in concentric shells, численного моделирования 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 нейтринным данным: 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 нейтринная томография 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 стандартной моделью 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 нейтринных сечений 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 стандартной модели), astrophysics (understanding космических лучей and their role in generating нейтрино), 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 нейтрино interaction cross section at extreme energies, where deviations from the стандартной модели are possible. It also contributes to understanding the acceleration of космических лучей, which determine the flux of atmospheric нейтрино.
🎯 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