Astronomers Were Confused By Bizarre TV Signals Coming From the Sky for 5 Years — Until Recently

Environmental pollution is all around us, one kind that is visible while there is another that does not catch the human eye but still exists, that is, radio-frequency pollution. With advancing communication technology, the Earth’s sky has transformed into a web of radio-frequency interference (RFI) that has only made the work of astronomers greatly challenging. Jonathan Pober, a physicist at Brown University in Rhode Island, USA, was keen on devising a method to eliminate the rogue and unwanted signals that disturb data sets collected from radio telescopes. So, when he detected a stray TV signal bouncing off an airplane via a high-precision telescope, an impromptu technique helped him trace the RFI and the possible source it was being emitted from, per a report by Brown University. 

Pober teamed up with Brown Ph.D candidate Jade Ducharme to execute his strategy devised to remove unwanted RFI interrupting the Murchison Wide-field Array (MWA), a telescope with 4,096 antennas installed in a no-signal zone in Western Australia. Pober serves as the U.S. science lead for the MWA project. Perplexed by the TV signals detected in the quiet zone regulated by the Australian government to minimize interference with the telescope, Pober had an epiphany. “It then hit us. We said, 'I bet the signal is reflecting off an airplane,’” the scientist recalled in the official statement on the university’s website. He shared that these TV signals had been picked up for nearly five years and had a rough idea about the airplane hypothesis. 

“Several people had suggested they were airplanes reflecting television broadcasts. We realized we might actually be able to confirm this theory for once,” the physicist said. By then, both Pober and Ducharme were confident that this experiment could lead to a bigger solution of identifying and filtering out stray signals. Hence, the scientific duo morphed two tracking techniques into a combination– the near-field corrections, which adjust the telescope to focus on objects closer to Earth, and the beamforming method that sharpens the focus of any object with a more precise “beam” pinpointing at the direction of the interference. They were able to track the airplane from which the TV signals had been bouncing off and calculated it to be flying above 38,400 feet with a speed of 492 miles per hour. 

As a final step, the source of the stray TV signals was identified as a frequency band associated with Channel 7, a local Australian digital TV channel. Pober acknowledged that the success of the investigative mission was a “key step” in eliminating human-made interference from data sets obtained during observations. “By accurately identifying and removing only the sources of interference, astronomers can preserve more of their observations, reduce frustrating data loss, and increase the chances of making important discoveries,” he marked.

According to a register chart published by the United Nations Office for Outer Space Affairs, 11,330 satellites were perched in Earth’s orbit in June 2023. The number has since increased with several more satellites launched in the past year. This poses a challenge for precision in astronomical research preventing high-quality radio observations due to interference from “satellite constellations,” Pober informed. The MWA telescope is particularly affected by these interferences because it observes the entire sky at once thus, adjusting its angle away from the satellites is entirely impossible. Consequently, all collected datasets that show RFI are trashed with much valuable data lost.