Astronomical radio sources are also very far away, despite their density. So the tiny signal reaching Earth is very weak: a single cell phone on the Moon’s surface would outshine all but the brightest.

Communication signals from Earth-orbiting satellites are much stronger, but limited by regulations to certain wavelengths. They are also known to radio astronomers who can filter them out. But radiation leak may cause artificial signals at undesirable wavelengths. The leak is often caused by human activity on Earth, but as the number of satellites has literally skyrocketed, astronomers are starting to worry about the impact from space. Now the team has announced the first detection of this electromagnetic interference from satellites.

“Radiation leakage from artificial satellites first appeared in our minds as a possible obstacle about two years ago,” recalls Benjamin Winkel (Max Planck Institute for Radio Astronomy, Germany and the Radio Astronomical Frequencies Committee, France). “At the time, no one knew how strong such an effect would be and whether it was just a theoretical issue.”

So Winkel, along with a few colleagues from other institutions affiliated with the Square Kilometer Observatory (SKAO), decided to take a look. They used the Low Frequency Array Array (LOFAR) base antennas in the Netherlands to search for signals from satellites in the SpaceX Starlink array. At this time, there were approximately 2,100 Starlinks in orbit; now there are more than 4,000.

What they found did not allay their fears. Of the 68 observed satellites, 47 were detected at frequencies from 110 to 188 MHz. This radiation leakage is significantly lower than the 10.7 to 12.7 GHz radio frequencies used for downlink signals. Federico Di Vruno (SKAO and Radio Astronomical Frequencies Committee, France), Winckel and colleagues Astronomy and Astrophysics.

Unwanted emissions are not unexpected. “Every electrical device creates a radiation leak,” explains team member Deulah Joges (also from the Max Planck Institute for Radio Astronomy in Germany and the Radio Astronomy Frequencies Committee, France). “There’s nothing you can do to prevent it other than affecting the strength of these signals.”

Indeed, every electrical appliance in your room, every circuit in your computer or phone acts as a tiny antenna that emits additional electromagnetic radiation. Manufacturers ensure that this radiation does not interfere with other devices (or even the device itself), but there is no reasonable way to eliminate it completely.

The same is true for orbiting electronics. “Compared to communication signals, satellites emit radiation, as a rule, they are millions of times weaker,” explains Winkel. “But it’s still good enough for us radio astronomers; It’s brighter than most astronomical sources we’ve observed.”

By looking at Starlink satellites, the team was able to follow the radio signals as they crossed the sky, showing that most of the radiation came from the satellites themselves rather than reflections from other radio sources. (A particular frequency comes from a powerful space surveillance radar in France that bounces off some satellites.)

The signal leak the team found is much stronger than a single satellite still meeting regulatory thresholds would allow. However, the rules set by the International Telecommunication Union (ITU) only apply to intentional radio emissions.

The leak problem is not limited to Starlink. Any working satellite emits some kind of radiation leak. What a change in numbers: More satellites in the sky make it more likely that one of them will pass through the relatively narrow field of view of radio telescopes on the ground.

“We usually remove satellite-contaminated data from further processing,” says Jozha. “The more often this happens, the more time we lose for follow-up.” For time-dependent observations, this can mean loss of important information. For example, astronomers may miss detections of mysterious Fast Radio Bursts (FRBs), which are extremely powerful radio emissions that last for a few seconds at most.

Jozha says even greater concerns, which can lead to false results when using typical noise reduction techniques, are weaker, unidentified signals lurking in background noise. Radiation leakage also becomes more pronounced at low frequencies, broadening the scope of radio astronomy research. Observatories designed specifically to detect these frequencies are likely to be affected, such as the LOFAR, the Long Wavelength Array in New Mexico, or the low-frequency portion of the SKA to be built in Australia.

Technical solutions can only alleviate but not solve the problem. Any attempt to do so will require the assistance of satellite operators, but for the time being such cooperation will be purely voluntary. Radiation leaks, no matter how severe, don’t break any rules: “From a radio astronomer’s point of view, unwanted electromagnetic emissions are currently poorly regulated for satellites and spacecraft,” the research team wrote.

So far, researchers have only taken an hour’s “snapshot” of one type of satellite using a telescope. They found that the radio signal varied from satellite to satellite, and some were not detected at all at the observed frequencies. Follow-up observations over the next year will provide a more global picture of how much radiation leak Starlink satellites produce.

But these initial results already show the need for action, Jozha concludes: “We believe that early recognition of this situation gives astronomy and operators of the major constellations the opportunity to actively work together on technical mitigations, in line with the necessary discussions to develop developments in the relevant charter.” Source