Elusive ‘Geoneutrinos’ Are Building a New Map of Earth’s Volatile Interior

The archetypal version of this story appeared in Quanta Magazine.

In a laboratory 2 kilometers underground, a crane lowers Matt Depatie, a detector technologist, done a hatch into a white-walled cavern filled with astir 7,000 tons of ultrapure h2o that glows arsenic bluish arsenic wiper fluid successful the light. “Splashdown,” Depatie says implicit a vigor arsenic helium steps into an inflatable raft waiting below.

Normally, the cavern is 1 of the darkest places connected Earth, but contiguous it is lit up for maintenance, offering america a uncommon accidental to spot inside. I adjacent done the hatch astatine Depatie arsenic helium paddles implicit to analyse the submerged experiment. He’s inspecting a house-sized detector built to drawback immoderate of the astir elusive particles known to physics: neutrinos.

This is the SNO+ neutrino experiment, buried heavy wrong the Creighton excavation astatine Snolab, an underground physics laboratory successful Sudbury, Canada. SNO+ consists of an acrylic sphere lined with astir 10,000 delicate airy detectors and filled with 780 tons of oily liquid scintillator, which flashes erstwhile lit up by energetic particles. The h2o astir the instrumentality and the stone supra it shield the detector from the glare of cosmic radiation, allowing the flickers of less communal particle interactions to radiance through.

Our full travel down has been portion of the crusade to support implicit darkness, adjacent beyond the disposable spectrum of light. As we descended the main shaft and walked done a rocky passageway to the lab, our bodies and apparel collected infinitesimal amounts of radioactive radon dust. Before entering the main laboratory space, we tossed our excavation clothes, showered, and changed into electrical bluish jumpsuits and hairnets to minimize the contamination we carried successful with us. “The showers aren’t for you,” Depatie said arsenic we changed, “they’re for the science.”

Such extremes are indispensable erstwhile you’re trying to catch ghosts—in this case, ghosts that whitethorn assistance uncover the secrets of inaccessible regions heavy wrong the Earth.

Neutrinos are the astir abundant of each the particles that person mass. But that wide is tiny: conscionable a millionth of the wide of an electron. With specified small heft and a neutral electromagnetic charge, the particles hardly ever interact with different matter. Trillions of neutrinos—mostly those produced successful the sun—pass done our bodies each second, yet aft years of hunting them with detectors specified arsenic SNO+, researchers person captured lone a fewer 100 1000 of their precious flashes.

Even much elusive—so overmuch truthful that aft decades of searching, scientists person detected lone a fewer 100 of them—are geoneutrinos.

Geoneutrinos are produced successful processes that vigor the interior of the planet. This vigor plays a large relation successful powering the travel of rocks successful the mantle, which shapes everything from sheet tectonics to Earth’s magnetic field. It comes from 2 main sources: vigor near implicit from the planet’s formation, and vigor produced by the decay of uranium, thorium, and potassium successful the rocks of the mantle and crust. Without this 2nd source, Earth would person agelong since cooled disconnected and go a tectonically dormant planet.

In counting geoneutrinos, physicists tin get a nonstop measurement of Earth’s captious heat-producing elements. “It’s the 1 happening we bash that focuses connected the Earth,” said Ryan Bayes, a particle astrophysicist astatine Queen’s University successful Ontario who works connected SNO+. “Everything other we bash is much focused connected what we person from other places successful the universe.”

The archetypal detection of geoneutrinos, by an instrumentality successful Japan called Kamland, was reported successful 2005. In 2009, the Borexino detector successful Italy reported catching respective twelve more. In November 2025, SNO+ reported its archetypal detection, bumping up the fig of observed geoneutrinos by astir 50.

What makes the detections astatine SNO+ peculiar is the experiment’s location: These are the archetypal geoneutrinos measured successful the occidental hemisphere, offering a caller position connected Earth’s radioactive interior.

Major uncertainties stay successful interpreting the results from these experiments, but researchers’ champion estimates suggest that each tract is measuring a antithetic flux. “It could beryllium that that’s the archetypal hint that the mantle is not uniform,” said Mark Chen, a particle astrophysicist astatine Queen’s University and manager of the SNO+ collaboration.

Geochemists person conventionally assumed that radioactive elements are distributed evenly passim the mantle, due to the fact that the flowing stone should premix everything together. But the measurements of geoneutrinos successful antithetic locations could hint that this is not the case.

The regions that look to beryllium producing the astir geoneutrinos beryllium astir supra continent-size blobs of anomalously hot, dense material, known arsenic ample low-shear-velocity provinces, oregon LLSVPs, which seismologists person mapped connected either broadside of the core. One is nether Africa, the different nether the Pacific Ocean. “There whitethorn beryllium deep Earth structures successful the mantle that are not understood,” Chen said. “It could beryllium that [they] ore immoderate kinds of elements.”

Neutrinos could 1 time connection caller penetration into the inactive mysterious root of these heavy structures and, much broadly, the patterns successful the mantle that underlie galore aspects of the Earth system. “It truly would beryllium a mode to marque a chemic representation of the Earth’s interior,” said William McDonough, a geochemist astatine the Chinese Academy of Sciences who has agelong been a starring dependable successful the hunt for geoneutrinos.

The outstanding question is whether the geoneutrino measurements uncover differences betwixt the areas of mantle beneath each experiment, oregon if the imbalance originates successful the mode the antithetic experiments number their geoneutrinos. Researchers crossed the committee accidental there’s inactive truthful overmuch uncertainty that it’s intolerable to say.

“If we instrumentality it astatine look value, we could accidental possibly the occidental hemisphere has a batch much radioactive worldly successful it than the eastbound hemisphere,” McDonough said. But determination are reasons to beryllium wary of these estimates. “Are the Italians right? Are the Japanese right? Are they some right? Or is thing wrong?” helium said.

The uncertainties associated with each detector’s results travel from the sorting process that physicists spell done to place geoneutrinos, Bayes said. “They don’t conscionable amusement up and say, ‘Hi, I’m a geoneutrino.’”

Scientists indispensable destruct signals from particles with excessively overmuch energy, particles with the incorrect measurement of a spot called helicity, and particles that they expect to spot flowing from atomic reactors. They indispensable besides destruct geoneutrinos coming from Earth’s crust, with the largest publication coming from the country wrong a fewer 100 kilometers of the detector. When those different detections are subtracted from the full count, the geoneutrino awesome from the mantle should beryllium each that’s left.

In wide terms, the geoneutrino flux from the mantle seems to beryllium precise precocious astatine Borexino and precise debased astatine Kamland, though the uncertainties are great. A elaborate geological mentation of the SNO+ results is inactive successful the works, Chen said, but truthful acold scientists spot a “pretty in-between” mantle beneath Canada.

A peculiar situation for SNO+ scientists is knowing the neutrinos coming from the detector’s surroundings, including a basin formed 1.8 cardinal years agone by a elephantine impactor. “There are tons of unknowns successful this geological area,” said Virginia Strati, a researcher astatine the University of Ferrara successful Italy who helped make a local model of radioactivity for Snolab.

Uncertainty besides comes from estimates of the full magnitude of radioactive worldly heating the mantle. The flux of geoneutrinos suggests that these elements could lend anyplace from conscionable a tiny percent of its vigor to fractional of it—a discrepancy equivalent to the output of tens of thousands of atomic powerfulness plants.

Both sources of uncertainty marque it adjacent much hard to observe immoderate differences betwixt the chemic constitution of peculiar sections of the mantle. The quality successful the geoneutrino flux expected from assorted distributions of radioactive elements “is precise small, and is hidden successful these uncertainties,” Strati said.

The detection at SNO+ comes astatine an breathtaking infinitesimal for geoneutrino research: JUNO, different immense neutrino experimentation currently collecting data successful China, is expected to study its archetypal geoneutrino flux aboriginal this year, adding a 4th and notably richer view. With much than 20,000 tons of scintillator, the experiment—buried nether a upland extracurricular the metropolis of Guangzhou — is truthful ample that it is expected to observe much geoneutrinos successful its archetypal twelvemonth than the combined output of Kamland, Borexino, and SNO+ implicit decades.

Clearer estimates of the geoneutrino flux astatine each experimentation could travel from much elaborate geological data, arsenic good arsenic further geoneutrino counts astatine each site. However, McDonough says the champion happening would beryllium to physique a neutrino detector astatine the bottommost of the ocean. It’s an thought McDonough has championed for decades.

Such a detector would beryllium acold from continental rocks, which are affluent successful radioactive elements; oceanic crust is besides thinner and much uniform. Crust-related uncertainties spell down truthful overmuch that “you are successful mantle-only territory,” helium said.

The thought of an ocean-bottom detector, estimated to outgo hundreds of millions of dollars, has seen small take-up from authorities funders to date. But McDonough is hoping helium tin marque thing hap successful China, which has fixed the greenish airy to different big geoscience projects. “It’s precise possible,” helium said. Until then, physicists volition support paddling astir for answers heavy underground.

Original story reprinted with support from Quanta Magazine, an editorially autarkic work of the Simons Foundation whose ngo is to heighten nationalist knowing of subject by covering probe developments and trends successful mathematics and the carnal and beingness sciences.