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

Uncertainty also comes from estimates of the total amount of radioactive material heating the mantle. The flux of geoneutrinos suggests that these elements could contribute anywhere from just a small percentage of its heat to half of it—a discrepancy equivalent to the output of tens of thousands of nuclear power plants.

Both sources of uncertainty make it even more difficult to detect any differences between the chemical makeup of particular sections of the mantle. The difference in the geoneutrino flux expected from various distributions of radioactive elements “is very small, and is hidden in these uncertainties,” Strati said.

The detection at SNO+ comes at an exciting moment for geoneutrino research: JUNO, another huge neutrino experiment currently collecting data in China, is expected to report its first geoneutrino flux later this year, adding a fourth and notably richer view. With more than 20,000 tons of scintillator, the experiment—buried under a mountain outside the city of Guangzhou — is so large that it is expected to detect more geoneutrinos in its first year than the combined output of Kamland, Borexino, and SNO+ over decades.

Clearer estimates of the geoneutrino flux at each experiment could come from more detailed geological data, as well as further geoneutrino counts at each site. However, McDonough says the best thing would be to build a neutrino detector at the bottom of the ocean. It’s an idea McDonough has championed for decades.

Such a detector would be far from continental rocks, which are rich in radioactive elements; oceanic crust is also thinner and more uniform. Crust-related uncertainties go down so much that “you are in mantle-only territory,” he said.

The idea of an ocean-bottom detector, estimated to cost hundreds of millions of dollars, has seen little take-up from government funders to date. But McDonough is hoping he can make something happen in China, which has given the green light to other big geoscience projects. “It’s very possible,” he said. Until then, physicists will keep paddling around for answers deep underground.

Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.