Astronomers built a neutrino telescope 3km under the sea — here's why

The Cubic Kilometre Neutrino Telescope, or KM3NeT, will take up enough ocean to fill 400,000 Olympic swimming pools.
Chris Young
One of the ARCA telescope balls.
One of the KM3NeT telescope spheres.


Neutrinos are abundant — scientists believe that billions of neutrinos pass through our bodies every second — but they are amongst the most elusive particles in the cosmos when it comes to actually observing and collecting data.

They are so elusive and challenging to detect due to the fact that they barely interact with their surroundings. Interestingly, this is, in fact, their secret power. It is why astronomers have built some of the most unusual observatories ever seen to detect the elusive particles.

One example comes from the Cubic Kilometre Neutrino Telescope, or KM3NeT, which is currently being constructed off the coast of Sicily, Italy, in the Mediterranean Sea.

Why detect neutrinos in the first place?

Though they are so hard to detect, neutrinos, also known as "ghost particles", can carry information about distant regions of the cosmos that would otherwise be degraded.

In fact, the very thing that makes them so hard to detect is also what makes them so valuable as an observation tool. Unlike photons or light particles, neutrinos are largely undisturbed by matter and electromagnetic fields, meaning they don't suffer the same degradation while traveling the vast expanse of space.

This means that neutrinos have the potential to provide even more information than our most state-of-the-art space observatories, such as the James Webb Space Telescope. Neutrinos can originate at supernovae, merging stars, and other exotic cosmic events, which could provide valuable data.

Meet the KM3NeT underwater telescope

Scientists are building KM3NeT beneath the surface of the Mediterranean to detect super-energetic neutrinos that have come from distant galaxies. Once finished, it will be made of hundreds of thousands of spherical detectors attached to strings and suspended vertically from the bottom of the sea like kelp.

As the name suggests, KM3NeT will take up one cubic kilometer of water for 400,000 Olympic swimming pools. It will be made up of more than 6,000 spheres, each containing 31 highly sensitive detectors called photomultiplier tubes.

Key to the construction are these separate ball-shaped spheres or telescopes. The video above shows one of these large balls being slowly rolled into the ocean. Once in position, they will be anchored roughly three and a half kilometers under the sea and used to wait for flashes of radiation that occur when the so-called ghost particles interact with the surrounding water.

Why build KM3NeT beneath the ocean?

The ocean is an ideal location for the KM3NeT telescope because the Antarctic is a good location for the IceCube Neutrino Observatory.

The IceCube observatory has been operating since 2011, and it uses detectors drilled into a cubic kilometer of pure ice. Observations from IceCube led to the first evidence that some neutrinos come from blazars — a highly active type of galaxy powered by a black hole.

The detectors used by KM3NeT and the IceCube observatory look for flashes of Cherenkov radiation. This is light that neutrinos produce when they interact with ice or water molecules. The detectors can read those flashes, allowing scientists to determine where the neutrino came from as well as other data, such as how it may have formed.

One of the reasons the KM3NeT team decided to build a submerged telescope rather than using ice is that water scatters light less. This makes it easier to get a more accurate idea of where the neutrinos come from. However, water also absorbs light more, meaning there is less light to work with.

We will start to get an even better idea of the differences between the KM3NeT telescope and the IceCube Neutrino Observatory as the former grows and continues to collect new data on the elusive ghost particles from the distant cosmos.

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