For centuries, scientists have tried to answer the question, “What’s the Earth made of?” While drilling projects and geological studies have revealed clues about the planet’s crust, the deeper layers remain largely inaccessible.
Now, researchers at Queen’s University are turning to an unlikely source of information—subatomic particles known as geoneutrinos—to probe the planet’s interior.
The research comes from a Queen’s-led team working with the SNO+ neutrino detector at SNOLAB in Sudbury, Ontario. Located two kilometres underground to shield it from radiation and other interference, the detector is designed to capture faint flashes of light produced when neutrinos interact with a liquid scintillator, a solution of organic compounds that emits light when exposed to radiation, inside a spherical tank.
In an interview with The Journal, Alex Wright, associate professor in the Department of Physics, Engineering Physics, and Astronomy at Queen’s, defined a geoneutrino.
“Geoneutrinos are a type of antineutrino, subatomic particles that are produced by decay of trace radioisotopes in the Earth.”
Since geoneutrinos are so tiny, nearly a billion times smaller than a proton, they can travel through solid matter almost unhindered, and they carry information about the chemical composition of the planet’s interior. The particles offer scientists a rare window into the planet’s interior, which is otherwise impossible to sample directly.
“We can sample the surface, and with a couple of kilometers down from the surface, we can drill sample holes and try to estimate beyond that. But the content of the mantle and the core, the inner layers of the earth, really isn’t known,” Wright noted.
By measuring geoneutrinos, researchers can infer the presence of radioactive materials deep underground.
“One clue we can gain into what the composition is, is by looking at how many of these antineutrinos there are, which gives us some information about what’s going on in the middle of the Earth,” Wright shared.
According to Wright, understanding these particles could also help answer a long-standing question about the planet’s heat.
“We know from geophysical measurements that the Earth is giving off terawatts of heat, but we don’t know whether the Earth is still cooling down or not. By measuring the geoneutrino flux, we hope to figure out whether there’s enough radioactivity in the Earth to be supplying the heat or whether the Earth is still cooling.”
However, detecting these particles is challenging. According to Dr. James Page, a postdoctoral researcher in the Department of Physics, Engineering Physics, and Astronomy, and the principal analyst on the project, the SNO+ detector at SNOLAB is designed to overcome these obstacles.
“One of the challenges is the rate of geo-neutrinos is really low, so they get drowned out by all sorts of radioactive backgrounds,” Page said.
“The other difficult hurdle to overcome is that they’re all very low in energy. So, you need really sensitive detectors […] these are what are called liquid scintillator detectors…to be able to pick out these really low energy events,” Page added. “But the detector is very clean. So, there are very low ambient background rates. It’s deep underground, so you get less cosmic rays coming in.”
The results mark the first time geoneutrinos have been detected in Canada, making SNO+ the third detector in the world to measure them, following similar experiments in Japan and Italy.
Observations from different regions are crucial for understanding how geological structures, such as the Canadian Shield, affect the particles being detected. Situated on the Canadian Shield, a vast region of Precambrian rock, the detector sits above a thick section of Earth’s crust.
“The Canadian Shield is really thick. So, the crust there is around 40 kilometres thick, which is significantly thicker than at the other two sites where geoneutrinos have been measured,” Page noted.
The project brings together particle physicists and geologists, combining expertise from both fields to interpret what these signals reveal about the Earth’s internal structure. The study’s findings were first presented at the Neutrino Geosciences 2025 conference hosted by Queen’s.
By comparing measurements from different parts of the world, researchers hope to determine whether the particles originate in the planet’s crust or deeper layers such as the mantle.
Researchers say studying geoneutrinos could answer fundamental questions about the planet, including how much of Earth’s heat comes from radioactive decay and how much remains from its formation billions of years ago. It may also shed light on whether the mantle is chemically uniform or made up of distinct regions with different compositions.
For scientists studying the deep Earth, geoneutrinos drifting silently through the planet may offer one of the clearest windows yet into a place we can’t reach.
Tags
Core, earth, Geology, Geoneutrino
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