Work starts on first deep-sea neutrino telescope in western Pacific Ocean

Led by Shanghai Jiao Tong University, a group of scientists and engineers has started constructing the first deep-sea neutrino telescope in the western Pacific Ocean to detect and analyze neutrinos from the universe to diagnose the origin of cosmic rays and explore the mysteries of the extreme universe, scientists involved in the project announced in Shanghai on Tuesday.

The Tsung-Dao Lee Institute at Shanghai Jiao Tong University said it has published the conceptual design of the TRopIcal DEep-sea Neutrino Telescope (TRIDENT) project in the science journal "Nature Astronomy."

According to the team led by the institute, they have selected a site on a deep-sea plain in the northern part of the ocean, approximately 3.5 kilometers deep. The seabed is flat, and the current flow is very gentle within a few hundred meters of the sea floor.

According to the team, they will anchor 1,200 vertical strings, each 700 meters long and spaced 70-100 meters apart, to the seabed like seaweeds. Each string carries 20 high-resolution digital optical modules. Spanning a 4-kilometer diameter, the array will cover 12 square kilometers and monitor around 8 cubic kilometers of seawater for high-energy neutrino interactions. The designed lifespan is 20 years.

The team will build a small-scale telescope with 10 strings by 2026 to test related technologies. The whole TRIDENT array is expected to discover neutrinos from the active galaxy NGC 1068 within one year of its operation, according to Xu Donglian, spokesperson of the project.

The neutrino telescope utilizes the Earth as a shield, capturing neutrinos that penetrate from the planet's opposite side. Located near the equator, TRIDENT can detect neutrinos from 360 degrees of the entire sky due to the Earth's rotation, complementing IceCube in Antarctica and other Northern Hemisphere neutrino telescopes, Xu noted.

Scientists said the project will not only bridge the existing gaps in China's research in this area but also contribute to the global multi-messenger astronomical network.

Furthermore, it promises to advance cutting-edge interdisciplinary research across particle physics, astrophysics, geophysics and marine sciences.

Jing Yipeng, leader of the project, pointed out that since the invention of the telescope by Galileo, astronomical observations have primarily depended on capturing photons from cosmic sources for centuries, using instruments such as the Hubble and James Webb Space Telescopes.

Yet, the universe communicates through various "messengers."

Neutrinos rank among the most abundant subatomic particles in the universe, with hundreds of trillions emanating from the Sun and passing through our bodies every second. Electrically neutral and primarily interacting via the weak force, they act as ghost-like travelers through the cosmos.

"Neutrinos, known for their ghost-like ability to penetrate matter, can escape from intense cosmic events such as supernova explosions and black hole eruptions," said Jing.

"This makes them ideal messengers for studying the universe's most extreme phenomena. Detecting these neutrinos not only helps us understand the mechanisms behind these powerful events but also offers insights into fundamental physics."

Although neutrinos were predicted in 1930 and first detected in 1956, their exploration has since earned four Nobel Prizes. These studies have revolutionized scientists' understanding of fundamental physics. Yet many mysteries, such as their precise mass, remain unsolved.

In the 1960s, Soviet physicist Moisey Markov first proposed to "determine the direction of charged particles with the help of Cherenkov radiation", which had inspired physicists to build neutrino telescopes.

In 2013, the IceCube Observatory in the Antarctic Pole detected cosmic high-energy neutrinos, and in 2015, the Laser Interferometer Gravitation Wave Observatory identified the merger of two black holes via gravitational waves. These milestones heralded the era of multi-messenger astronomy, which integrates data from photons, gravitational waves and neutrinos.

Today, the IceCube project, located 2,500 meters deep in Antarctica, stands as the world's leading neutrino telescope. Other projects, such as KM3NeT in the Mediterranean and Baikal-GVD in Lake Baikal, enhance these endeavors.

As neutrino astronomy approaches significant breakthroughs, there's a global push to develop next-generation telescopes for deeper exploration of the cosmos and a better understanding of fundamental physics, Jing observed.