The IceCube Neutrino Observatory has been the world’s largest neutrino telescope since 2010. Its kilometer-cubic-kilometer volume of instrumented Antarctic ice has produced foundational results: the first detection of astrophysical neutrinos in 2013, the first identified cosmic neutrino source (TXS 0506+056) in 2017, the Glashow resonance event in 2021, the first observation of our own galaxy’s neutrino glow in 2023, and the identification of NGC 1068 as a steady neutrino source in 2022.
What it has not yet done is identify large numbers of cosmic sources. IceCube’s existing rate of identified sources is, by 2026, three: TXS 0506+056, NGC 1068, and the Milky Way diffuse glow. The diffuse extragalactic neutrino flux is much larger than these three contributions, meaning that most cosmic neutrinos are coming from sources we have not yet been able to point at.
The planned IceCube-Gen2 expansion is designed to change that. The new instrument will be roughly eight times the volume of the existing IceCube, add a dedicated radio-detection array for the highest-energy neutrinos, include a low-energy infill called PINGU optimized for atmospheric oscillation physics, and provide a surface array for cosmic-ray tagging and improved background rejection.
By the time it is fully operational in the 2030s, IceCube-Gen2 should multiply the rate of identified cosmic neutrino sources by roughly an order of magnitude, push the maximum detectable neutrino energy beyond 100 PeV, and produce the most precise atmospheric oscillation measurements of any experiment yet.
The four components
The IceCube-Gen2 design has evolved over several years through community planning processes. The current baseline includes four distinct subsystems.
The optical array. About 120 new strings of digital optical modules, deployed in the ice in a region adjacent to and surrounding the existing IceCube detector. Each new string carries about 80 optical modules. The spacing between strings is wider than in the original IceCube — about 240 meters instead of 125 — because the new science focus is on high-energy events that produce long, easily-tracked tracks. The total instrumented volume is roughly 8 cubic kilometers.
PINGU (Precision IceCube Next Generation Upgrade). A low-energy infill deployed inside the existing DeepCore region of IceCube. PINGU adds about 40 additional dense strings with tighter spacing, lowering the energy threshold from a few GeV down to about 1 GeV. The science target is precision atmospheric neutrino oscillation, including a measurement of the mass ordering.
The radio array. A separate detection system covering a much larger area — roughly 500 square kilometers of ice surface, with antennas distributed at various depths and on the surface. The radio array is sensitive to in-ice neutrino-induced showers at energies above about 100 PeV, where the resulting electron-positron plasma emits a coherent radio pulse called Askaryan radiation. The radio array dramatically extends the energy reach beyond what optical detection can do.
The surface array. A network of cosmic-ray detectors above the IceCube and Gen2 footprint, used to identify and veto cosmic-ray events that could otherwise produce backgrounds in the deep array.
Why expand the optical volume
The astrophysical neutrino spectrum that IceCube measures falls steeply with energy, but it does not fall arbitrarily fast. The rate of events above any energy threshold scales roughly as the instrumented volume. Doubling the volume doubles the rate. Multiplying the volume by eight multiplies the rate by eight.
The expected science yield from the volume expansion includes:
More identified sources. With eight times the data, the statistical significance with which any given candidate source can be identified scales as √8 ≈ 2.8. Sources currently at the 4σ level should reach 5σ or beyond with full Gen2 exposure. Many sources currently invisible should rise above the threshold.
Improved angular resolution. A larger array catches each event with more modules, which improves the directional reconstruction. The expected angular resolution for high-quality track events is about 0.3°, down from about 0.5° for the existing IceCube.
Better spectral measurements. With more events per energy bin, the shape of the cosmic neutrino spectrum can be measured in more detail. This constrains the underlying source populations and acceleration mechanisms.
More transient response. The faster event rate means that follow-up campaigns to multi-messenger triggers (gravitational waves, gamma-ray bursts, optical transients) will have a higher chance of catching a coincident neutrino event.
Why the radio array
Optical Cherenkov detection works well from a few GeV up to about 10 PeV. Above that, the showers from neutrino interactions become so long that they extend out of the instrumented volume. The detection efficiency drops rapidly. To go higher, you need a different technology.
The Askaryan effect, predicted by Gurgen Askaryan in 1962 and confirmed experimentally in 2003, provides that different technology. When a high-energy electromagnetic shower develops in a dense dielectric medium like Antarctic ice, the shower develops a small negative charge asymmetry — the result of positron annihilation and electron acquisition from the ice during the shower evolution. The asymmetric charge cloud, moving faster than light in ice, emits coherent radio waves at wavelengths comparable to the shower length.
The radio signal can propagate through kilometer distances of ice with relatively little attenuation. A relatively sparse array of radio antennas can therefore monitor a vast volume of ice — much larger than the optical array can practically instrument.
The IceCube-Gen2 radio component targets neutrinos with energies above about 100 PeV. At these energies, the dominant expected source is cosmogenic neutrinos — neutrinos produced when ultra-high-energy cosmic rays scatter off cosmic microwave background photons (the GZK process). Detecting cosmogenic neutrinos would directly probe the highest-energy cosmic-ray accelerators in the universe.
Current radio prototypes — ARA, ARIANNA, RNO-G — have been demonstrating the technique for years at modest scales. IceCube-Gen2 will scale up the approach to its first kilometer-scale instrument.
What PINGU adds
PINGU’s mission is different from the rest of Gen2. While the optical and radio arrays target high-energy astrophysical neutrinos, PINGU targets atmospheric neutrinos at GeV energies — the same energy regime where oscillation effects from matter passing through the Earth produce signatures sensitive to the mass ordering.
The basic idea: atmospheric neutrinos arriving from below have passed through different amounts of Earth depending on their zenith angle. At specific energies near 6-10 GeV, MSW resonances in the Earth’s mantle produce flavor-dependent oscillation effects whose pattern depends on whether the mass ordering is normal or inverted. With enough statistics in the right energy range, PINGU can distinguish the two scenarios.
The expected sensitivity is comparable to (and complementary with) JUNO and the long-baseline experiments DUNE and Hyper-Kamiokande. A combined analysis of all these experiments could push the mass-ordering significance well past 5σ within a few years of all programs reaching maturity.
The deployment challenges
Building anything at the South Pole is hard. The summer construction season runs from about late October to mid-February. The continent is supplied by air and the population of researchers is small. Every component must be designed to function reliably for decades with no possibility of physical maintenance once deployed beneath the ice.
The deployment process for an IceCube string is itself an engineering achievement. A hot-water drill bores a hole through about 2.5 kilometers of ice, taking about 36 hours. The instrumented string is then lowered into the hole as the ice refreezes around it. Once frozen, the string is permanent.
For IceCube-Gen2, 120 new strings need to be deployed over multiple summer seasons. Each requires a hole drilled, a string lowered, and connections established to the surface infrastructure. The plan envisions about 12-15 strings per season for about 8-10 years of construction.
The radio array, in contrast, can be deployed without deep drilling. Most radio stations are placed at modest depths — 10 to 100 meters — and can be installed much faster. The total radio deployment is expected to proceed in parallel with the optical deployment.
Funding and approval
IceCube-Gen2 is a US-led international collaboration involving institutions from over a dozen countries. As of 2026, the project has been through multiple stages of NSF (US National Science Foundation) review and international funding-agency discussions. Different components have somewhat different approval statuses.
The radio array has received initial funding to begin pilot deployment. The optical and surface components are in advanced planning, with substantial preliminary funding allocated for design and prototype work. Final approval and full construction funding is expected within the next few years.
What the field looks like with Gen2
By the time IceCube-Gen2 is fully operational — likely the mid-2030s — the neutrino astronomy landscape will look quite different from today.
Two large neutrino telescopes will be running: IceCube-Gen2 at the South Pole and KM3NeT in the Mediterranean. Both will be roughly comparable in capability, but with different sky coverage and different systematic uncertainties. Other projects — Baikal-GVD in Russia, P-ONE proposed in the Pacific, TRIDENT and HUNT proposed in China — may also be operational.
This network of large detectors will provide:
- Continuous all-sky monitoring for transient events.
- Dozens of identified cosmic neutrino sources, mapping out the neutrino sky in detail.
- Multi-messenger alerts within seconds of any significant event.
- High-precision measurements of the diffuse cosmic neutrino spectrum.
The field will move from its current state — where the first few identified sources are still being celebrated — to a mature observational science with statistical power comparable to gamma-ray astronomy. The discovery rate will accelerate substantially.
The next decade
IceCube-Gen2 is one of several major neutrino projects in the planning or construction phase. Together with DUNE, Hyper-Kamiokande, JUNO, and the various next-generation 0νββ experiments, they constitute the largest concentration of new neutrino experiments since the first wave of underground detectors decades ago.
What will come out of them, collectively, is the maturation of neutrino physics into a field with the kind of precision and observational reach that other physics subfields have long enjoyed. The 2030s should be a decade in which most of the major outstanding neutrino questions are settled, and in which neutrino astronomy joins gamma-ray and gravitational-wave astronomy as a routine multi-messenger discipline.
The expansion under the South Polar ice is one of the bigger pieces of that picture.
For the current IceCube detector, see Inside IceCube. For the other major neutrino telescope, see KM3NeT. For the parallel ground-based programs, see JUNO, DUNE, and Hyper-Kamiokande. For the highest-energy neutrinos the radio array will probe, see The Glashow resonance.
Frequently asked
What is IceCube-Gen2?
IceCube-Gen2 is the planned next-generation neutrino observatory at the South Pole, building on the existing IceCube detector. The plan includes an optical array roughly eight times the existing IceCube volume, a surface array for cosmic-ray tagging, a low-energy infill called PINGU optimized for atmospheric oscillation studies, and a separate radio-detection array at much higher energies.
When will it be built?
Construction is expected to begin in the late 2020s, with deployment continuing through the 2030s. The full instrument is targeted for completion in the early-to-mid 2030s. The radio component may begin operations earlier in stages. As of 2026, the project has been through multiple stages of design review and is in advanced planning.
What new physics will it enable?
Several things: a much higher rate of identified cosmic neutrino sources (perhaps dozens within a decade of operation), better angular resolution for multi-messenger astronomy, sensitivity to the highest-energy cosmogenic neutrinos through the radio array, and improved precision on neutrino oscillation parameters through the low-energy PINGU extension. It will also push down the threshold for the highest-energy neutrino events the field can detect.
Why two different detection technologies?
Because optical Cherenkov detection and radio detection cover different energy regimes. Optical detection works well from a few GeV up to about 10 PeV — IceCube's existing range. Radio detection of in-ice showers becomes practical above about 100 PeV, where the signal generates a coherent radio pulse called Askaryan radiation. The two technologies are complementary; together they would span six orders of magnitude in energy.
How does it compare to KM3NeT and other neutrino telescopes?
IceCube-Gen2 will remain the world's largest neutrino telescope in terms of instrumented volume. KM3NeT in the Mediterranean and Baikal-GVD in Russia have complementary strengths — different sky coverage, different systematic uncertainties, somewhat better angular resolution in some regimes. The neutrino-astronomy community now thinks of these as a network rather than as competing projects, with each contributing to a multi-site observation strategy.
Cite this article 5 formats
APA
Neutrino Times Editorial Team. (2025, September 29). IceCube-Gen2: the planned eightfold expansion of the South Polar neutrino observatory. Neutrino Times. https://neutrino-times.com/articles/icecube-gen2-south-pole-expansion/
Chicago
Neutrino Times Editorial Team. "IceCube-Gen2: the planned eightfold expansion of the South Polar neutrino observatory." Neutrino Times, September 29, 2025. https://neutrino-times.com/articles/icecube-gen2-south-pole-expansion/.
MLA
Neutrino Times Editorial Team. "IceCube-Gen2: the planned eightfold expansion of the South Polar neutrino observatory." Neutrino Times, 29 Sep. 2025, https://neutrino-times.com/articles/icecube-gen2-south-pole-expansion/.
BibTeX
@misc{neutrino-times-icecube-gen2-south-pole-expansion,
author = {Neutrino Times Editorial Team},
title = {IceCube-Gen2: the planned eightfold expansion of the South Polar neutrino observatory},
howpublished = {Neutrino Times},
year = {2025},
month = {sep},
url = {https://neutrino-times.com/articles/icecube-gen2-south-pole-expansion/},
note = {Accessed: 2025-09-29}
} RIS
TY - GEN TI - IceCube-Gen2: the planned eightfold expansion of the South Polar neutrino observatory AU - Neutrino Times Editorial Team PY - 2025 DA - 2025-09-29 PB - Neutrino Times UR - https://neutrino-times.com/articles/icecube-gen2-south-pole-expansion/ ER -