Five steel frames on the floor of Lake Superior, wired to shore through a disused pipe at a small-town water plant: that is the plan physicists at the University of Minnesota Duluth have drawn up to catch neutrinos, the ghostly particles that pour through every human body by the billions each second.
The project, proposed by UMD with partner laboratories around the United States, would sit offshore from Two Harbors, a harbor town on the lake’s Minnesota shore. Minnesota’s pollution control agency put a draft water-quality certification for it out for public comment, describing a run of about one year that needs no environmental mitigation.
How the setup works
According to the state’s notice, the five frames would rest on the lakebed and each would be tied to land by its own underwater cable. Rather than cutting a new trench across the beach, the cables would come ashore through an unused pipe at the Two Harbors water intake plant.
Why a lake? Detecting neutrinos is a numbers game. “Our detectors have to do two things,” UMD physicist Alec Habig explained in a university explainer on neutrinos. “They have to be big, so we have a lot of bullseyes. And they have to be able to see the results of charged particles flying off.” A deep, cold, very clear body of water offers both bulk and a dark backdrop for the faint flashes those particles leave behind.
Why neutrinos are so hard to catch
Neutrinos carry no electric charge, so they slip through the mostly empty space inside atoms. Habig compares an atom to a ballpark with the nucleus as a baseball on the pitcher’s mound; a neutrino only registers if it strikes a target he likens to “a speck of dust 1000 times smaller than the baseball.”
That rarity is extreme. “If I live to be 80, it’s a coin flip that even one tripped over something in my body,” Habig said. A quick sum puts that in perspective: 80 years is about 2.5 billion seconds, so with billions of neutrinos crossing you every second, quintillions pass through a lifetime and perhaps one, maybe none, ever hits anything.
When one does collide, the charged debris that flies off can be tracked, and physicists work backward like a pool player reading a break. “Now we can say we see the neutrino, even though we never saw it,” Habig said.
What it could tell us
Neutrinos are produced inside our own star, in exploding stars and around black holes, and they cross the universe nearly undisturbed, so a captured one can point back to where it came from. Minnesota already has deep roots in the field: Fermilab, near Chicago, fires the world’s strongest human-made neutrino beam through the Earth toward detectors in the north of the state.
For more on the cosmic engines that make such particles, read our piece on how pulsars hint that supermassive black hole pairs do merge, or browse the latest from our science desk.
The limits
This is a short trial, not a permanent observatory. The state describes a project of about a year, and neither UMD’s explainer nor the permit notice lists a target number of detections. Habig is frank about how early the field remains: “We’re at the stage of the puzzle-building where we’re opening the box,” he said. The draft certification’s public comment period has already closed.
Further reading
Image: James St. John, CC BY 2.0 via Wikimedia Commons
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