Strange radio pulses detected coming from ice in Antarctica
Several years ago, a cosmic particle detector in Antarctica observed a series of unusual radio signals, according to an international research group that includes scientists from Penn State. The strange radio pulses were detected between 2016 and 2018 by NASA’s Antarctic Impulsive Transient Antenna (ANITA), a range of instruments flown on balloons high above Antarctica that are designed to detect radio waves from cosmic rays hitting the atmosphere, and a new study provides additional context to the nearly decade-old results.
The goal of the ANITA experiment was to gain insight into distant cosmic events by analyzing signals that reach the Earth. Rather than reflecting off the ice, the signals — a form of radio waves — appeared to be coming from below the horizon, an orientation that could not be explained by the current understanding of particle physics and may have hinted at new types of particles or interactions previously unknown to science, the team said at the time.
A new study using the Pierre Auger Observatory in Argentina analyzed 15 years of cosmic data to try to make sense of those signals. The team of international scientists, including Penn State researchers, recently published their results in the journal Physical Review Letters.
“The radio waves that we detected nearly a decade ago were at really steep angles, like 30 degrees below the surface of the ice,” said Stephanie Wissel, associate professor of physics, astronomy and astrophysics who worked on the ANITA team searching for signals from elusive particles called neutrinos. "While the origin of these events is still unclear, our new study indicates that such events have not been seen by an experiment with a long exposure like the Pierre Auger Observatory. So, it does not indicate that there is new physics, but rather more information to add to the story."
She explained that by their calculations, the anomalous signal had to pass through and interact with thousands of kilometers of rock before reaching the detector, which should have left the radio signal undetectable because it would have been absorbed into the rock.
“It’s an interesting problem because we still don't actually have an explanation for what those anomalies are, but what we do know is that they're most likely not representing neutrinos,” Wissel said.
Neutrinos, a type of particle with no charge and the smallest mass of all subatomic particles, are abundant in the universe. Usually emitted by high-energy sources like the sun or major cosmic events like supernovas or even the Big Bang, there are neutrino signals everywhere. The problem with these particles, though, is that they are notoriously difficult to detect, Wissel explained.
