Universe Today
Picture this…. you’ve spent five years building an exquisitely sensitive scientific instrument. You’ve tested it, shipped it halfway around the world, reassembled it in Antarctica, and now you’re watching it disappear into the blue sky aboard a giant balloon. For the next three weeks, all you can do is monitor it from the ground and hope everything works.
That’s exactly what happened to a team of University of Chicago scientists who launched the PUEO experiment on December 20th, 2024. PUEO (which stands for Payload for Ultrahigh Energy Observations) spent 23 days floating at 120,000 feet above Antarctica, searching for particles that have never been detected before. The quarry? Ultra high energy neutrinos, some of the most elusive and energetic particles in the universe.
The Payload for Ultrahigh Energy Observations (Credit : NASA/NASA/Scott Battaion)
Neutrinos are fascinating things. They’re constantly raining down on Earth from outer space, passing through matter as if it barely exists. Most of the time we don’t notice them at all, they interact so weakly with ordinary matter that they can sail right through the entire planet without touching anything.
But scientists believe there’s a rare subset of neutrinos that are extraordinarily energetic. These would carry more energy than even the particles being smashed together at the Large Hadron Collider in Europe. Finding them would give us a window into the universe’s most violent events, the places where such energetic particles could be created, like the vicinity of supermassive black holes or collisions between ultra dense neutron stars. The challenge is actually catching one and so to do that, the PUEO team came up with an ingenious solution to use the entire continent of Antarctica as a detector.
Superconducting quadrupole electromagnets are used to direct the beams in the Large Hadron Collider (Credit : Gamsiz)
The idea works because ice conducts radio waves extremely well. If one of these ultra high energy neutrinos happened to collide with an atom in Antarctica’s enormous ice sheet, the impact would produce radio waves that travel through the ice and into the air above. PUEO was designed to catch those faint signals from its vantage point at the edge of space.
The instrument itself is remarkable with 96 ultra sensitive radio antennas arranged in concentric circles, surrounding a “brain” that constantly sifts through incoming signals to identify which might be neutrinos. It’s powered by solar panels and built to be significantly more sensitive than its predecessor, ANITA, thanks to advances in electronics and a clever design that combines signals from multiple antennas in real time.
Building PUEO was a global effort. Over five years, labs around the world built components and shipped them to Chicago for assembly. Then came the testing phase which included a trip to Texas to make sure the electronics would function in the near vacuum conditions of the stratosphere, where there’s no air for cooling fans.
“The big challenge is that without air, you can’t use fans to cool down the electronics if they get too hot,” - Cosmin Deaconu, a research professor at UChicago who wrote the flight software.
After passing its tests, PUEO had to be taken apart again for an epic journey by road to California, by ship to Christchurch in New Zealand, and finally by air to NASA’s balloon station in Antarctica. There, scientists worked quickly to reassemble it before the launch window opened. The weather needs to be not just clear, but stable all the way up through the atmosphere. And the launch window can open any time of day or night, so the team had to be constantly ready.
PUEO got lucky, it launched successfully on its first attempt in the early morning of December 20th. First the balloon rose, then it lifted the instrument, until the entire 700 foot long assembly was airborne. As it climbed to 120,000 feet, the solar panels extended, and additional antennas deployed below the main instrument to boost sensitivity.
But the launch was just the beginning. For the next three weeks, the team took shifts monitoring PUEO around the clock. The instrument was designed to function independently, but they still had to make adjustments, at one point, the payload was rotating more slowly than expected, meaning one side was getting too much sun and overheating.
PUEO is hunting for high energy particles such as those emitted by gamma ray bursters. This animation shows GRB 211106A, one of the most energetic sGRB ever registered, as seen by the Atacama Large Millimetre/submillimetre Array (Credit : ALMA (ESO/NAOJ/NRAO))
After 23 days aloft, with weather predictions suggesting the winds would change, the team made the call to bring PUEO back down. NASA cut the line to the balloon and deployed a parachute. The instrument drifted gently back to Earth about 200 miles north of the South Pole. A retrieval crew traveled to the landing site to recover the “black box” containing 50 to 60 terabytes of data collected during the mission. That precious cargo will be flown back to Chicago, where the real work begins: sorting, calibrating, and analysing the data to see if PUEO caught any of these extraordinary particles.
The scientists expect it will take about a month just to process all the data, with first results available in roughly a year. They might discover the highest energy particles ever detected, or they might not find any at all but either way, they’ll learn something valuable about the most extreme environments in our universe.
Source : In Antarctica, balloon lands after 23-day search for particles from outer space
