Astronomers have detected a mysterious digital signal, with its source located surprisingly close to us.

The sky is filled with radio frequency interference, but thanks to astronomers who tracked a stray television signal reflected off a passing airplane, a new method may emerge to eliminate some of the uncontrolled signals that hinder radio telescopes from observing space. The study was published in the journal Publications of the Astronomical Society of Australia, reports Space.

Currently, there are over 10,000 satellites in low Earth orbit, most of which are designed to transmit various messages via radio waves. However, due to the radio frequency interference generated by these satellites, radio telescopes struggle to conduct high-quality observations of the cosmos.

This issue is particularly relevant for the Murchison Widefield Array (MWA) radio telescope located in Australia. It consists of 4,096 antennas designed to detect low-frequency radio waves in the range of 70 to 300 MHz, which carry information from the epoch of reionization of the universe, when the first stars and galaxies were formed. Since the MWA observes the entire sky simultaneously, there is no way to direct the antennas away from the satellites.

Because radio frequency interference occurs randomly and it is difficult to pinpoint its source, filtering the data from space observations becomes problematic. Typically, datasets contaminated by radio interference are simply discarded by astronomers, resulting in the loss of a significant amount of valuable data. However, the case of the wandering television signal has given astronomers hope that there may be a way to salvage some of this data.

The MWA radio telescope is located within a 300-kilometer-wide radio quiet zone, yet it continuously picks up television signals that should not be transmitted in this area. The origin of these signals has been a mystery, but scientists hypothesized that such signals could be reflecting off airplanes.

The authors of the study combined two methods to track the source of the radio interference and were able to trace the television signal back to an airplane flying at an altitude of 11 km and a speed of 792 km/h. The researchers even found that the television signal was within the frequency range used by an Australian digital TV channel. This signal was being broadcasted from somewhere outside the radio quiet zone and was reflected off the aircraft's body.

This identification of the source of radio interference can serve as a model for further data filtering, preserving valuable information about space. By accurately identifying and removing only the sources of interference, astronomers can retain more of their observations, reduce the frustrating loss of data, and increase the chances of important discoveries, the scientists say.

However, tracking the source of radio frequency interference to a passing airplane was just the first step. The next step is to learn how to remove similar signals from astronomical data and then to figure out how to eliminate not only television signals reflected off airplanes but also signals from satellites. Given the vast number of satellites, this is a significantly more complex task.