Science & Discovery
Losing Silence
New sources of radio pollution threaten astronomy’s “quiet zones.”
By Briley Lewis
Image by Gerd Altmann from Pixabay
L ook up at the sky in any city and you can clearly see the effects of light pollution drowning out the stars. At the same time — invisible to the unaided eye — radio pollution is overpowering faint signals from the cosmos.
Astronomers collect information across the electromagnetic spectrum — including radio waves — and by combining these different wavelength windows, they can reveal a more complete picture of the cosmos. Astronomers have studied the universe in radio wavelengths for decades. Radio telescopes have been mostly shielded from the consequences of technology, operating in radio quiet zones (their equivalent of a dark sky site) and protected radio frequency bands not allowed for other use.
“Radio astronomy allows us to conduct fundamental research that complements optical and higher energy telescopes and other instruments,” wrote Federico Di Vruno and Mathieu Isidro, members of the Square Kilometer Array Observatory collaboration and the International Astronomical Union’s Center for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (IAU CPS), in an email with Mercury. As with remote optical observatories, however, a similar pollution problem is occurring in various radio windows of the electromagnetic spectrum. Satellite constellations are rapidly encroaching on these protections, threatening the night sky as we know it. “By polluting the radio environment in the skies,” they add, “we are slowly closing windows.”
The Green Bank Observatory was founded in 1956, and the National Radio Quiet Zone established in 1958. The observatory's 300-foot dish, shown here, began studying the radio sky in 1962. That telescope collapsed in 1988, but the observatory has since built other radio instruments, including the Green Bank Telescope.
[NRAO/AUI/NSF]
The two largest satellite constellations orbiting Earth are Eutelsat OneWeb (at left or above) and SpaceX Starlink. Shown here are data visualizations using publicly accessible data.
[satellitemap.space]
Radio astronomy's importance
Many objects in the cosmos naturally emit radio waves, including the Sun, planet-forming disks of gas around other stars, supermassive black holes at the centers of galaxies, and pulsars, the rapidly spinning remnants from a supernova explosion. The most luminous active galactic nuclei — supermassive black holes devouring matter and spewing out energy — were even first observed in the radio in the 1950s, and referred to as quasi-stellar radio sources, or quasars for short. More recently, the first image of a black hole’s shadow famously plastered on headlines across the globe in 2019, was created by the Event Horizon Telescope, a network of radio telescopes around the world.
Observations of radio waves from space are even relevant to our daily lives here on Earth. Geodesy, the study of precisely measuring Earth’s shape and orientation in space, is critical to the functioning of GPS systems—and, it relies on observations of very steady, reliable radio sources from beyond the Milky Way to define our planet’s orientation.
Particular frequencies of radio waves are reserved for astronomy and astronomy only. Other technologies — like cellphones, satellites, TV broadcasts, and more — are not allowed to use these bands, which are determined and enforced by the International Telecommunication Union, a United Nations agency originally established in 1865 as the International Telegraph Union. “Radio astronomers have been working for more than 50 years in this environment to protect the frequency bands allocated to radio astronomy,” explain Di Vruno and Isidro. However, “with the advancement of technology and science, radio astronomers now need to observe in much wider portions of the radio spectrum, even in parts that are allocated to other users.”
For years, astronomers have worked out how to observe in non-protected frequencies by creating “radio quiet zones” around major observatories to reduce interference. In the United States, the National Radio Quiet Zone surrounding the Green Bank Observatory covers 13,000 square miles around West Virginia and Virginia. In the town of Green Bank, cell phones, microwaves, Wi-Fi, and other radio-using technologies are actually banned by law. Even the most restrictive quiet zone on the ground, however, is no match for radio bright satellites whizzing overhead.
The National Radio Quiet Zone spans some 13,000 square miles surrounding Green Bank Observatory and the Sugar Grove Research Station (a National Security Agency site).
[Green Bank Observatory]
One of the first observed extraterrestrial radio detections came from the active centers of galaxies, an example of which is illustrated here.
[ESO/M. Kornmesser]
Humanmade constellations add to the noise
Satellite constellations — groups of satellites coordinated together to provide communications services — pose a substantial threat to astronomy. They operate in a large chunk of the radio spectrum, and are more prevalent in the sky than any previous single satellite. “Definitely the biggest challenge for radio quiet zones is the large satellite constellations,” wrote Di Vruno and Isidro.
“Every satellite, even ones we think of as inconsequential, are orders of magnitude stronger than even the most powerful of radio sources, let alone the faint signals that many astronomers are attempting to observe,” adds Nicholas Luber, a radio astronomer at Columbia University in New York City. “As the radio sky becomes more and more crowded, we will lose our ability to study a wide range of phenomena — from large-scale magnetic fields to millisecond bursts of extraordinary energy to the evolution of neutral gas, which acts as the raw fuel for the formation of stars.”
IAU CPS is already working with satellite operators to reduce the effects on radio quiet zones, and there is ongoing research to get the whole picture of satellites’ radio emissions, from both their intentional downlinks in addition to other unintended radiation, to hopefully inform the designs of future satellites. The Low-Frequency Array (known as LOFAR) recently observed radio emission from Starlink satellites far outside their typical downlink frequencies, illustrating how the effects might reach further than previously thought. Scientists’ efforts to advise designs and operations, however, rely on the cooperation of private companies, which is not guaranteed.
In a recent study, astronomers with the LOFAR radio telescope reported the array had detected radio signals from electronics onboard SpaceX Starlink satellites. Such satellites, illustrated here above LOFAR, are a major source of noise and radio pollution for astronomy.
[ASTRON/Daniëlle Futselaar]
How else can we protect the quiet sky?
As private industry increasingly ventures beyond Earth, there is a strong need for improved regulation. Di Vruno and Isidro explain how this could take the form of special considerations for radio quiet zones, or even laws — at all levels, from local to international — surrounding unintended emissions from satellite constellations. They also describe a need for private companies to commit to sustainable use of Low-Earth Orbit, a region of space rapidly filling up with human-made junk, whether that’s by improving their technologies, finding ways to clean up obsolete spacecraft in orbit, or simply launching fewer satellites.
Satellites and the constellations they comprise have many important and positive uses for humanity, such as GPS and bringing access to the internet to remote locations. But the high number of spacecraft required in these satellite constellations also has the potential to be destructive to the environment both on and off Earth.
“One could think of this as the same situation that happened with plastics, a great technology that was used without regard for its environmental impact and resulted in countless horrible effects,” said Di Vruno and Isidro. “Hopefully we are in time to avoid having a similar situation in outer space.” ✰
(Published May 2, 2024)
BRILEY LEWIS (she/her) is a freelance science writer and Ph.D. Candidate/NSF Fellow at the University of California, Los Angeles, studying Astronomy & Astrophysics. Follow her on X @briles_34 or visit her website.
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