Mysterious Radio Pulses Found in Antarctica Seem to Defy Physics, and Researchers Are Trying to Trace Their Origins
Strange signals detected by a NASA instrument more than a decade ago have continued to confound scientists, but a new paper rules out cosmic neutrinos as a source
Nearly ten years ago, scientific instruments picked up strange radio pulses in Antarctica. Now, in a study recently published in Physical Review Letters, researchers take us a step closer to figuring out their origins.
The signals were uncovered between 2016 and 2018 by NASA’s Antarctic Impulsive Transient Antenna (ANITA), which used balloons to send detection instruments more than 18 miles above the icy continent in an attempt to identify neutrinos.
Neutrinos are high-energy cosmic particles that are abundant throughout the universe. But due to their vaporous nature, they can pass through many types of matter, even stars, and remain unchanged. This makes neutrinos incredibly difficult to detect, and physicists have nicknamed them “ghost particles” for that reason. Neutrinos do interact with water and ice, however, producing pulses of radio waves and showers of particles that can help scientists find them with powerful instruments.
Once detected, neutrinos can reveal impressive information about the nature of cosmic events that took place light-years away, as Stephanie Wissel, an astrophysicist at the Pennsylvania State University, says in a statement. Since neutrinos don’t interact with much of anything, researchers should be able to trace their direction of travel backward to their point of origin, likely a super-powerful cosmic event.
Did you know? Ghost particles are abundant but elusive.
Neutrinos, or “ghost particles,” are the universe’s most common particles with mass. Approximately 100 trillion neutrinos pass through your body every second, but you don’t even notice.
ANITA is meant to detect radio pulses emitted by neutrinos as they move through the ice. But its mysterious signals appeared to come from far below the horizon—passing through thousands of miles of Earth’s rocky interior. These pulses seemed to defy current understandings of particle physics, since radio waves caused by neutrinos are not expected to be able to pass through so much rock.
“They are expected to arrive from slightly below the horizon, where there is not much Earth for them to be absorbed,” Justin Vandenbroucke, a physicist at the University of Wisconsin–Madison who was not involved in the research but peer-reviewed it, tells CNN’s Ashley Strickland. Models predict these pulses would come in at angles of only one to five degrees below the horizon—these came through the ice at a much sharper 30 degrees, leaving researchers unable to identify their origins.
Since then, physicists have been trying to understand the nature of these strange signals—such as whether the findings could have been a fluke or could point to the existence of particles or interactions previously uncharted.
The recent study used the Pierre Auger Observatory in Argentina, bringing together hundreds of scientists from around the world to analyze 15 years of cosmic data in an attempt to explain ANITA’s results.
The observatory employed two different methods in an attempt to find the same signals ANITA did, as reported by CNN. The first method tried to find high-energy particles through tracking their interaction with water in tanks on Earth; the second method looked for particles’ interactions with ultraviolet light high in the atmosphere.
But the team couldn’t find any evidence of similar signals detected by Pierre Auger, nor could researchers find similar events in data from the IceCube Experiment in Antarctica, which is also searching for neutrinos.
The study concluded that the signals detected by ANITA could not have been caused by neutrinos, thus characterizing them as “anomalous.” The study was also able to clarify that noise and other known particle interactions did not contribute to the signals. Yet, though they ruled out a few possible hypotheses, scientists are still not sure what exactly caused the strange radio pulses.
“More research needs to be done on this,” study co-author Benjamin Flaggs, a physicist at the University of Delaware, tells Live Science’s Perri Thaler. “There are theorists proposing some beyond-standard-model interactions from different types of particles.”
“My guess is that some interesting radio propagation effect occurs near ice and also near the horizon that I don’t fully understand, but we certainly explored several of those, and we haven’t been able to find any of those yet either,” Wissel adds in the statement.
Scientists, including Wissel, are now hoping that more advanced instruments might bring them closer to an answer to this decade-long physics mystery. Wissel is now working with the Payload for Ultra-high Energy Observations (PUEO), a new balloon-based detector that is larger and ten times more sensitive than ANITA.
“I’m excited that when we fly PUEO, we’ll have better sensitivity,” Wissel says in the statement. “In principle, we should be able to better understand these anomalies, which will go a long way to understanding our backgrounds and ultimately detecting neutrinos in the future.”