Within Antarctic ice, the IceCube Neutrino Observatory is recording rare astronomical phenomena. Constructed in the harsh conditions of the South Pole, it is the first detector of its kind. But now, a sister project is underway — one located over 2,600 meters beneath the surface of the Pacific Ocean.
Called the Pacific Ocean Neutrino Experiment (P-ONE), it will be built off the coast of Washington State in the Cascadia Basin with global collaboration including Georgia Tech’s Ignacio Taboada.
Taboada, who is the current spokesperson of the IceCube collaboration and a professor in the School of Physics, has been awarded over $1.5 million in funding through a Major Research Instrumentation grant from the National Science Foundation (NSF) to build P-ONE’s sensor trigger system, which will record and identify sources of light as they are captured by the telescope’s sensors.
“This is a multi-institute collaboration,” Taboada shares. Co-PI’s include Naoko Kurahashi Neilson of Drexel University, Nathan Whitehorn and Tyce DeYoung of Michigan State University, and Alexandra Rahlin of the University of Chicago.
2,600 meters under the sea
Taboada says the team was drawn to the underwater location, despite the associated building challenges because “the characteristics of the seawater mean that we could identify more individual sources better than IceCube can, if we can build a detector of the same size.”
Capturing astrophysical particles is a balance of finding the right medium for the sensors: the medium’s density contributes to how many particles are captured.
While an open-air observatory would be possible, Taboada explains that “air is about 1,000 times less dense, so it means that we would get 1,000 times fewer neutrinos interacting in the detector — and neutrino detections are very, very rare.” Using a medium like ice or seawater maximizes the possibility of capturing these particles.
Ice and seawater also present unique challenges. “The ice in Antarctica is extremely transparent,” Taboada explains. This means that when a photon enters the ice, it can travel a very long distance within that ice. “But it doesn't travel in a straight line,” he says. Instead, the particle ricochets and scatters, deviating from its original path.
This makes it more difficult to determine exactly where the particle has come from — a key aspect for astronomical observations. “In comparison, light entering seawater scatters much less," Taboada says. “It always travels in a straight line.” Because of this, neutrino directions are determined more precisely in seawater than in ice.
Tracing the cosmos
Key to capturing these particles is the trigger system that Taboada will build with this new funding. That component will collect data around interesting events, which are seen as light to the system.
But there are many sources of light in the ocean that aren’t from astronomical phenomena. “It's not something that can be trivially predicted,” says Taboada. “It's a very complicated situation and you have to adapt the trigger to various amounts of background light.”
For example, there’s bioluminescence to consider.
Some sources, like fish or small organisms, can move around independently, while others, like bioluminescent plankton, might instead react to turbulence. The trigger system will need to identify and filter out all of these sources.
“Seawater also has a lot of potassium,” Taboada adds. “One of the isotopes of potassium is radioactive, and the optical sensors can catch light from that.”
Once the trigger system recognizes and captures the event, the data is sent to the mainland, where computers will leverage machine and deep learning to determine exactly what the sensor has captured.
“It's a process of gathering and analyzing interesting data,” Taboada says, similar to looking into a night sky and differentiating shooting stars, constellations, satellites, and planes.
From sea to space
Because P-ONE is one of the first projects of its kind, the research team plans to initially install six or seven lines of instrumentation across the seafloor. “That is rather small,” says Taboada, “but it will demonstrate how to build the instrument and how to operate it.”
“P-ONE has the eventual objective of being similar to IceCube in size,” he adds. “But it will be a northern hemisphere detector (meaning it can ‘see’ different parts of the sky than IceCube), and should have significantly better angular resolution and sensitivity.” And while P-ONE’s location will provide views that IceCube can’t, the effort also has the potential to provide a new perspective of the ocean floor.
The system will continuously monitor the deep ocean at an unprecedented scale, capturing data about environmental conditions and biological processes, key information for oceanographers and marine biologists — all while furthering the field of neutrino astrophysics.
Funding: NSF
P-ONE is a collaboration between the following organizations:
Ocean Networks Canada; University of Victoria; University of Alberta; Department of Physics, Queen's University; Department of Physics, Simon Fraser University; TRIUMF; Department of Physics, Technical University of Munich; Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Centre for Astroparticle Physics; Collaborative Research Centre 1258 (SFB1258) at TUM funded by the Deutsche Forschungsgemeinschaft (DFG); European Southern Observatory; Institut für Kernphysik, Goethe Universität Frankfurt; GSI Helmholtzzentrum für Schwerionenforschung; Max Planck Institute for Physics; Institute of Nuclear Physics, Polish Academy of Science; University College London; Department of Physics and Astronomy, Michigan State University; Georgia Institute of Technology; Drexel University; University of Chicago
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School of Physics Professor Ignacio Taboda has been awarded over $1.5 million in funding to build P-ONE’s sensor trigger system.
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Written by Selena Langner
