Astronomers Want to Build a Neutrino Telescope. Using the Pacific Ocean?

Neutrino detectors are about to get a lot bigger.
Brad Bergan
A computer-generated image of glowing blue-green particles.piranka / iStock

One of the most mysterious particles in the universe are neutrinos, with only dark matter out-baffling scientists as a more puzzling phenomenon.

And while there are neutrino detectors in operation hunting for the rarified particles, we might need to resort to the colossal scales of the Pacific Ocean to detect a class of ultra-powerful neutrinos, according to a recent study shared on a preprint server.

And, with a small-scale demo in the works, we may soon see whether this idea will pan out, and transform our grasp of the universe.

We need a bigger neutrino detector

The universe generates neutrinos at a significant quantity. They are involved in the weak nuclear force, and play a crucial role in nuclear decay and fusion. In fact, wherever nuclear activity is going down, neutrinos aren't far, according to a report from The core of the sun, for example, is one unspeakably huge fusion reaction, which means neutrinos are continually firing away from it. Earlier studies on neutrinos have suggested that — when you hold your thumb up to the sun, roughly 60 billion neutrinos will pass through your thumbnail, every single second. That's a lot.

But the problem is how rarely neutrinos interact with ordinary matter, even though there are trillions and trillions flowing through your body per second. Despite this mind-numbing number, in one human lifespan only about one neutrino will ever directly interact with the atoms of your body. For decades, physicists thought the elusive neutrinos had no mass, moving through the cosmos at the speed of light. But, in time, evidence hinted that neutrinos have some mass, after all.

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Three kinds of neutrinos are known to scientists: the muon neutrino, the tau neutrino, and the electron neutrino. While each one has its own set of associated nuclear reactions, all three kinds can swap identities while in motion. This means even a breakthrough study that might capture one neutrino would only know a tiny sliver of the neutrino's existence, and very little of its "past lives", so to speak. And the most high-energy neutrinos are so rare that existing detectors like IceCube in Antarctica have only detected a handful of them. For our grasp of these mysterious and theoretically abundant particles to expand, we need a bigger detector.

A neutrino detector of unprecedented scale

This is why the Pacific Ocean Neutrino Experiment (P-ONE) might be necessary. Don't worry, it's not actually an ocean-spanning detector. It works like this: first, scientists find an isolated region in the Pacific, then we build unconscionably long strands of photodetectors (nearly a mile long, probably longer). The next step is to attach floats to the strands, so they can hang vertically in the water. P-ONE envisions 10 clusters of these insanely long strings, each with 20 optical features, for a total of 1,400 photodetectors gliding up and down in the Pacific, covering an area that's miles wide. This would be capable of detecting the little flashes of neutrinos when they hit the ocean.

Of course, there are problems with the design. For one, the strands won't really hold still in an ocean as monstrously huge as the Pacific. And the largest body of water on Earth isn't full of pure water, with plankton, salt, and a lot of fish excrement gliding around like a big mess. These and other goings-on of the Pacific will alter the light patterns between the strands, which means it won't be easy to measure neutrino interactions, and scientists will have to continually recalibrate the colossal contraption. As of writing, it doesn't exist, but the research team behind aims to construct a smaller, two-strand proof of concept in the coming years. If it works, we may be on the verge of a new kind of cosmic study, at unprecedented scales.