IceCube (2013): The First High-Energy Neutrinos From Space

The IceCube Collaboration reported in 2013 the first evidence for high-energy neutrinos from beyond the Solar System. Its detector, a cubic kilometer of Antarctic ice at the South Pole, caught 28 neutrinos, including two near 1 PeV, far more than particles made in Earth’s atmosphere could explain.

The question

Neutrinos are ghostly particles that almost never interact with matter. That makes them hard to catch, but it is also their strength: unlike charged particles, they travel without changing direction or losing energy, so they point straight back to where they were made. Astronomers had already caught neutrinos from the Sun, starting with Raymond Davis’s experiment in a South Dakota gold mine, and the Sudbury Neutrino Observatory showed in 2002 that neutrinos change flavor as they travel. The open question was whether the universe’s most violent objects also send very high-energy neutrinos our way, and whether a detector could separate them from the flood made in Earth’s own air.

What the paper found

• A two-year, all-sky search. IceCube looked at data from May 2010 to May 2012 for neutrinos interacting inside the detector, with energies from about 30 TeV up to the PeV range. One TeV is a trillion electronvolts; one PeV is a thousand times more.
• 28 events. The search found 26 new events on top of two PeV neutrinos reported earlier. Those two, at about 1 PeV, were the highest-energy neutrinos then observed.
• Too many to be local. The count was well above the expected background from cosmic rays striking the atmosphere.
• 4 sigma evidence. A purely atmospheric origin was rejected at the 4 sigma level. Sigma is a measure of how unlikely a result is under a “nothing new” assumption; 4 sigma is strong evidence, short of the 5 sigma physicists usually demand to claim a discovery.
• The right fingerprints. The flavors, directions and energies of the events did not match atmospheric backgrounds but fit an extraterrestrial component.

How they did it

The IceCube Neutrino Observatory instruments a cubic kilometer of ice with 86 vertical strings carrying 5,160 light sensors, buried between 1,450 and 2,450 meters deep. It was completed in December 2010. When a neutrino hits an atomic nucleus in the ice, it produces a flash of light that the sensors in the clear glacial ice can track. By keeping only events that began inside the detector, the team cut down the background of particles raining in from the atmosphere above.

Why it mattered

This was the first evidence for high-energy neutrinos from beyond the Solar System, and it opened neutrino astronomy at the highest energies. Physics World named it the 2013 Breakthrough of the Year. Neutrinos offer a way to see inside cosmic accelerators that light cannot escape, and a detector buried in ice joined the family of telescopes.

What we know now

IceCube went on to point at individual sources. In 2018 it traced a high-energy neutrino to the blazar TXS 0506+056. Later it found neutrinos from the galaxy NGC 1068, and in 2023 it mapped neutrino emission from the plane of the Milky Way. An upgrade adding more than 600 new and enhanced sensors was completed in early 2026.

In October 2026 IceCube’s principal investigator, Francis Halzen, received the 2026 Nobel Prize in Physics for decisive contributions to IceCube and the discovery of high-energy neutrinos of astrophysical origin.

Who wrote it

The paper is signed by the IceCube Collaboration, the international team that built and runs the detector, led by Halzen. He had first presented the idea of catching neutrinos in South Pole ice in 1988. Semantic Scholar lists about 1,470 citations (October 2026).

Read the original

IceCube Collaboration (2013). “Evidence for High-Energy Extraterrestrial Neutrinos at the IceCube Detector.” Science 342, 1242856. doi:10.1126/science.1242856

Free to read: arXiv preprint.