Inside the underground lab in China tasked with solving a physics mystery

A giant sphere 700 m underground with thousands of light-detecting tubes will be sealed in a 12-storey cylindrical pool of water in coming months for an experiment that will shine new light on elusive subatomic particles known as neutrinos.

A giant sphere 700 m (2,300 ft) underground with thousands of light-detecting tubes will be sealed in a 12-storey cylindrical pool of water in coming months for an experiment that will shine new light on elusive subatomic particles known as neutrinos.

After years of construction, the $300 million Jiangmen Underground Neutrino Observatory (JUNO) in China's southern Guangdong province will soon start gathering data on neutrinos, a product of nuclear reactions, to help solve one of the biggest mysteries in particle physics.

Every second, trillions of extremely small neutrinos pass through matter, including the human body. In mid-flight, a neutrino, of which there are three known varieties, could transform into other types. Determining which types are the lightest and the heaviest would offer clues to subatomic processes during the early days of the universe and to explaining why matter is the way it is.

To that end, Chinese physicists and collaborating scientists from all over the world will analyse the data on neutrinos emitted by two nearby Guangdong nuclear power plants for up to six years.

JUNO would also be able to observe neutrinos from the sun, gaining a real-time view of solar processes. It could also study neutrinos given off by the radioactive decay of uranium and thorium in the Earth to better understand mantle convection driving tectonic plates.

Due to go operational in the latter half of 2025, JUNO will outpace the far larger Deep Underground Neutrino Experiment (DUNE) under construction in the United States. DUNE, backed by the Long-Baseline Neutrino Facility (LBNF) under the U.S. Department of Energy's (DOE) top particle physics laboratory, Fermilab, will come online around 2030.

The race to understand neutrinos and advance the study of particle physics, which has transformed medical imaging technologies and developed new energy sources, intensified when the DOE abruptly cut funding for U.S. institutes collaborating on JUNO. It instead focused on building DUNE, which has since been plagued by delays and budget overruns, with costs skyrocketing to more than $3 billion.