Key Takeaways:
- Neutrinos are elusive particles, flooding through the cosmos and generated by nuclear reactions like those in the Sun.
- Neutrino detectors like IceCube and Kamiokande need massive volumes of water to capture neutrino interactions.
- High-energy neutrinos are extremely rare, requiring even larger detectors for proper study.
- The Pacific Ocean Neutrino Experiment (P-ONE) proposes using ocean depths as a massive neutrino detector.
- P-ONE would consist of photodetector “strands” in the Pacific, requiring constant calibration due to ocean movement and impurities.
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Every second, 60 billion neutrinos pass through your thumbnail from the Sun alone!
Neutrino Detectors and the Pacific Ocean Experiment
In the search to understand the cosmos, neutrinos—subatomic particles created in nuclear reactions—have become critical clues to some of physics’ most complex questions. Produced in vast quantities by processes such as nuclear fusion in the Sun, neutrinos are hard to capture due to their weak interactions with matter. On Earth, advanced detectors have been built to study them, including Japan’s Kamiokande and the IceCube Neutrino Observatory in Antarctica. Now, astronomers are setting their sights on a new frontier for neutrino observation: the depths of the Pacific Ocean.
Current Neutrino Observatories
Neutrinos, second only to dark matter in their mystery, play a key role in nuclear reactions. For example, every second, around 60 billion neutrinos produced in the Sun’s core pass through a thumbnail-sized area on Earth. Detecting neutrinos is challenging, however, due to their minimal interactions with other particles. Most pass through matter without leaving a trace. Yet when neutrinos do collide with water molecules, they emit a tiny flash of light. Special photoreceptors in detectors like Kamiokande, which used over 50,000 tons of water, or IceCube, which harnesses an entire cubic kilometer of Antarctic ice, capture these brief flashes, allowing researchers to measure neutrino direction and energy.
Despite these advances, ultra-high-energy neutrinos remain rare and difficult to detect. IceCube, after ten years of observation, has managed to capture only a handful of these high-energy particles, suggesting a larger-scale solution is needed. High-energy neutrinos are highly significant because they are produced by extreme cosmic events such as supernovae or colliding black holes, making them prime targets for research.
P-ONE: A Neutrino Detector in the Pacific Ocean
The proposed Pacific Ocean Neutrino Experiment (P-ONE) aims to transform a large area of the Pacific Ocean into a neutrino detector, expanding our ability to capture these elusive particles. The concept is straightforward: using long strands of photodetectors, approximately a kilometer in length, placed over a mile beneath the ocean surface, P-ONE would act as a “natural” neutrino detector. Designed as seven clusters, each consisting of ten strings with 20 optical elements, P-ONE would hold a total of 1,400 photodetectors spread across several miles of the Pacific, far exceeding the coverage of IceCube.
However, the unique properties of the ocean pose new challenges. Unlike the controlled ice of Antarctica, the ocean is a dynamic and complex environment, with the detectors needing to account for salt, plankton, and other particles that interfere with light, as well as constant movement in ocean currents. This variability demands continuous calibration to maintain measurement accuracy. To address these issues, P-ONE’s developers have planned an initial two-strand demonstration phase to test the concept before scaling up to full capacity.
If successful, P-ONE could enable new insights into the universe by capturing more of the rare, high-energy neutrinos and tracing their origins. Ultimately, the vast and deep waters of the Pacific could become the next frontier in astrophysics, helping researchers explore the most energetic and distant events in the cosmos.
Well, we are not using it for anything else anyway, might as well.
For some context we already have one in the deepest part of the ice at the South Pole. Plus another in lake Baikal in Russia and one in the Mediterranean although these are smaller and are still getting up to size of the one at the South Pole which, in turn, is currently being upgraded itself.
The idea is to instrument as large of a volume as possible. The reason why neutrino telescopes aren’t like electromagnetic (EM) telescopes is because neutrinos don’t interact much. For an EM telescope if a photon is coming at your detector, it will interact. For neutrinos, the vast majority of them stream right through the detector. So you not only want something big, but really you want some 3D so that if it interacts anywhere in the volume you can detect it. While this is obviously a disadvantage on the detecting side, it is advantageous in that it tells us different things about astrophysical objects since they are produced in slightly different ways and they travel through the universe relatively unimpeded, unlike photons at these energies.
The best way to detect the high energy1 neutrinos is to instrument a huge volume of water with particle detectors. Then, if a neutrino interacts anywhere in that volume, it will create a bunch of high energy secondary particles which, in turn, will Cherenkov radiate photons in the optical. Those photons will travel through the ice and some will hit a particle detector. By recording when, where, and how many photons are detected, the event can be reconstructed allowing for an estimate of the energy, direction, and flavor of the initial neutrino.
There are lots of unknowns that these experiments are probing. On the lower energy side of things they provide good information about neutrino oscillations which is a big unknown in particle physics. On the higher energy side of things they detect neutrinos from astrophysical processes which we don’t understand either. The experiment at the South Pole has been putting out great results for >1 decade now with lots of room for improvement.
Russia turned part of Lake Baikal into a neutrino detector.
Baikal is mentioned in the paper but the people who wrote it don’t introduce it as “by the way there’s already a smaller version of our crazy idea in a giant lake that is essentially a mini-ocean with fish and freshwater seals in it” and they should put it that way so it sounds less insane.
Super Kamiokande can detect antineutrinos from fission whenever a Japanese nuclear power plant a few kilometers away turns on, and one of the sources of noise for this project will be all the nuclear submarines in the Pacific. This is probably how both Russia and China found budget for neutrino detecting lakes. I hope someone in the Pentagon decides to give them a billion dollars but also allows them to do science.
The south pacific gyre has no currents and the lowest level of biological activity anywhere in the Earth’s oceans. Sounds like a good spot.
Yes, there is some concentration of plastic debris there. It floats on the surface and should not affect this instrument. The concentration is measured in tens of thousands of plastic particles per square km.
i mean…. it would be useful? but I suspect there’d be a lot of noise to account for. the ice of antarctica doesn’t experience hurricanes or currents. or fish.
I am seeing a lot of confusion and misinformation in this thread, and as a PhD student doing research in this field (neutrino physics/astronomy) I think I can offer some clarity.
This idea seems stupid and absurd
While this idea does seem crazy, it’s not that crazy. Multiple underwater neutrino detectors already exist like ANTARES in the Mediterranean and BDUNT (Lake Baikal). Others are already planned like KM3NET, NEMO, and NESTOR (all in the Mediterranean). They all consist of the same concept: strings of photomultiplier tubes sunk to the bottom of the lake/sea/ocean. What is new about P-ONE is it’s location in the Pacific, which may present difficulties different from those experienced in the past. Still though, this concept is not wildly new, and many methods of background rejection have already been developed in these previous experiments.
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