China's neutrino observatory nears completion, aiming to unlock cosmic mysteries

TL;DR: China has been building its underground neutrino detector for years. The device will soon come online, looking for different neutrino flavors in a massive trove of data. Meanwhile, two additional detectors will "double check" what China's researchers are doing in different parts of the world.

The Jiangmen Underground Neutrino Observatory (JUNO) is almost ready to start recording data about neutrinos floating around the universe. Located in the city of Kaiping, in the Guangdong province, the Chinese detector, which took $300 million and nine years to build, has now entered the final stage of construction. According to researchers, the detector's results will be amazing for the scientific community – if everything goes according to plan.

The JUNO detector is a giant orb-shaped device hidden 700 meters below a granite hill in southern China. The orb is full of a special liquid compound designed to emit light when neutrinos pass through it. After installation is complete, the orb will be completely submerged in purified water.

Neutrinos are extremely elusive particles that came to exist after the Big Bang, and they rarely interact with normal matter. These elementary particles are electrically neutral, and have so little rest mass that it was long thought to be essentially zero. Neutrinos are very difficult to study, so researchers have been building giant detectors around the world to maximize the chances of detecting neutrino interactions through weak force and gravity.

The JUNO detector will specialize in studying antineutrinos, neutrino antiparticles produced by two nuclear power plants located 50 kilometers from the submerged orb. Antineutrinos coming into contact with the liquid inside the orb should produce a sudden burst of light, which researchers would then be able to detect and record.

Neutrinos are known to come in three flavors: electron neutrino, muon neutrino, and tau neutrino. JUNO researchers are looking to rank the three distinct particles by their mass, solving one of the many questions nuclear physicists have speculated about since neutrinos were first experimentally detected in 1942.

The JUNO installation should become operational during the second half of next year, collecting data about potential neutrino-related reactions. Two additional large neutrino detectors are being built in Japan (Hyper-Kamiokande) and the US (DUNE), and are set to become operational in 2027 and 2031, respectively. Hyper-Kamiokande and DUNE will use different approaches to study neutrinos while also crosschecking JUNO's results.