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Neutrinos From Deep Inside Earth Provide a New Picture of the Mantle
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particle physics
Neutrinos From Deep Inside Earth Provide a New Picture of the Mantle
By
James Dinneen
August 7, 2026
A global constellation of neutrino detectors is creating a never-before-seen view of the radioactive elements that power Earth’s tectonic heat engine.
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The JUNO experiment, located outside the city of Guangzhou in China, is expected to report its first geoneutrino detections this year.
JUNO Collaboration
Introduction
By James Dinneen
Contributing Writer
August 7, 2026
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experimental physics
geophysics
neutrinos
particle physics
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In a laboratory 2 kilometers underground, a crane lowers Matt Depatie, a detector technologist, through a hatch into a white-walled cavern filled with about 7,000 tons of ultrapure water that glows as blue as wiper fluid in the light. “Splashdown,” Depatie says over a radio as he steps into an inflatable raft waiting below.
Normally, the cavern is one of the darkest places on Earth, but today, it is lit up for maintenance, offering us a rare chance to see inside. I peer through the hatch at Depatie as he paddles over to examine the submerged experiment. He’s inspecting a house-size detector built to catch some of the most elusive particles known to physics: neutrinos.
This is the SNO+ neutrino experiment, buried deep within the Creighton mine at Snolab, an underground physics laboratory in Sudbury, Canada. SNO+ consists of an acrylic sphere lined with nearly 10,000 sensitive light detectors and filled with 780 tons of oily liquid scintillator, which flashes when lit up by energetic particles. The water around the device and the rock above it shield the detector from the glare of cosmic radiation, allowing the flickers of less common particle interactions to shine through.
Our whole journey down has been part of the crusade to maintain absolute darkness, even beyond the visible spectrum of light. As we descended the main shaft and walked through a rocky tunnel to the lab, our bodies and clothes collected minute amounts of radioactive radon dust. Before entering the main laboratory space, we tossed our mine clothes, showered, and changed into electric blue jumpsuits and hairnets to minimize the contamination we carried in with us. “The showers aren’t for you,” Depatie said as we changed, “they’re for the science.”
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Matt Depatie, left, helps maintain the SNO+ detector, which reuses components of the SNO experiment that ran from 1999 to 2006.
James Dinneen
Such extremes are necessary when you’re trying to catch ghosts — in this case, ghosts that may help reveal the secrets of inaccessible regions deep within the Earth.
Radioactive Planet
Neutrinos are the most abundant of all the particles that have mass. But that mass is tiny: just a millionth the mass of an electron. With such little heft and a neutral electromagnetic charge, the particles hardly ever interact with other matter. Trillions of neutrinos — mostly those produced in the sun — pass through our bodies every second, yet after years of hunting them with detectors such as SNO+, researchers have captured only a few hundred thousand of their precious flashes.
Even more elusive — so much so that after decades of searching, scientists have detected only a few hundred of them — are geoneutrinos.
Geoneutrinos are produced in processes that heat the interior of the planet. This heat plays a major role in powering the flow of rocks in the mantle, which shapes everything from plate tectonics to Earth’s magnetic field. It comes from two main sources: heat left over from the planet’s formation, and heat produced by the decay of uranium, thorium, and potassium in the rocks of the mantle and crust. Without this second source, Earth would have long since cooled off and become a tectonically dead planet.
The SNO+ experiment sits deep underground, shielded from cosmic rays beneath 2 kilometers of rock.
Courtesy of Leo Duquette/SNOLAB
In counting geoneutrinos, physicists can get a direct measure of Earth’s vital heat-producing elements. “It’s the one thing we do that focuses on the Earth,” said...