China Builds World’s Largest Transparent ‘Ghost Particle’ Detector Sphere

The construction of the world’s largest transparent spherical detector has been completed deep beneath the surface in southern China.

This achievement for the Jiangmen Underground Neutrino Observatory (JUNO) is a project designed to study neutrinos. Neutrinos, known for their incredibly small size and near-zero interaction with matter, have long been a subject of fascination for scientists. Often called “ghost particles” due to their ability to pass through almost anything without detection, these particles are key to understanding some of the most profound mysteries in the cosmos.

According to scientists from JUNO, “neutrinos can easily zip through our body, buildings, or the entire Earth without being felt, hence earning the nickname ‘ghost particles.'”

The JUNO project, launched in 2015 as a collaboration between the Chinese Academy of Sciences (CAS) and the Guangdong government, is now nearing the final stages of completion, with the full operation of the facility expected in August 2025. The core component of the observatory is a massive acrylic sphere—standing 12 stories high and measuring 35.4 meters in diameter—that is positioned 700 meters underground. This placement shields the detector from cosmic rays and other forms of interference, ensuring highly accurate data collection.

Inside the sphere, 20,000 tonnes of liquid will be used to detect neutrinos. This liquid will emit flashes of light upon interacting with the particles, enabling scientists to observe and study them in detail.

“By studying neutrinos, we can understand why the universe has become what it is today, and what will be the future of the universe,” stated Wang Yifang, chief scientist of JUNO.

Neutrinos, despite their tiny and electrically neutral nature, travel at nearly the speed of light. These particles are present throughout the universe, originating from a wide range of events such as nuclear reactions within stars, supernova explosions, and radioactive decay within rocks.

“Since the Big Bang, they have permeated the entire universe,” the scientists highlighted in an official statement.

JUNO’s primary mission is to determine the neutrino mass hierarchy, a key factor in understanding how the universe has evolved. The facility’s strategic location—53 kilometers away from the Yangjiang and Taishan nuclear power plants—ensures the optimal study of neutrino oscillation, a process where neutrinos change types as they travel.

The observatory will also focus on detecting various phenomena, such as supernovae, solar neutrinos, and atmospheric neutrinos. With its unprecedented scale and sensitivity, JUNO is expected to detect a daily average of 40 reactor neutrinos, several atmospheric neutrinos, one geoneutrino, and thousands of solar neutrinos. Over six years, it is projected that JUNO will capture up to 100,000 neutrinos.

JUNO builds upon the successes of earlier experiments like the Daya Bay Reactor Neutrino Experiment, where Chinese and international physicists discovered a third type of neutrino oscillation in 2012.

Now, with larger capabilities and improved precision, JUNO is positioned to significantly advance the boundaries of neutrino research, bringing humanity closer to unraveling the secrets of the universe.