An exponential increase in the number of satellites placed in low-Earth orbit has brought advances in telecommunications including broadband access in rural and remote areas worldwide. It also has caused a surge in light pollution in space that imperils the work done by orbiting astronomical observatories.
A new NASA-led study focusing on four space telescopes - two currently operational and two planned - estimates that a large percentage of images obtained by these observatories over the next decade could be tainted by light emitted or reflected by satellites sharing their low-Earth orbit.
The researchers calculated that about 40% of images taken by NASA's Hubble Space Telescope and about 96% of those taken by the U.S. space agency's SPHEREx observatory could be contaminated by light from satellites. They also calculated that about 96% of images from the European Space Agency's planned ARRAKIHS observatory and China's planned Xuntian telescope could be similarly affected.
Hubble would be less affected due to its narrow field of view, the researchers said.
Orbiting telescopes are a vital part of space exploration. They can observe a wider range of the electromagnetic spectrum than ground-based telescopes, and the lack of atmospheric interference lets them get sharper images of the cosmos, enabling direct imaging of distant galaxies or of planets beyond our solar system.
"While until now most light pollution came from cities and vehicles, the rise of telecommunication satellite constellations is rapidly starting to affect astronomical observatories worldwide," said astronomer Alejandro Borlaff of NASA's Ames Research Center in California, lead author of the study published in the journal Nature.
"As telescopes stare at the universe attempting to unveil distant galaxies, planets and asteroids, satellites sometimes cross in front of their cameras, leaving bright traces of light that erase the dim signal that we receive from the cosmos. This was a known problem for ground-based telescopes. But until now, space telescopes - much more expensive and placed in apparently pristine vantage points of view in space - were thought to be almost free of human-made light pollution," Borlaff said.
In 2019, there were roughly 2,000 satellites in low-Earth orbit. The number now is around 15,000. Borlaff said that proposals from industry foresee around 560,000 satellites in low-Earth orbit in the coming decade.
"To give an idea of how much this number increased recently, we have launched more satellites to low-Earth orbit in the last four years - 2021 to 2025 - than in the previous seven decades of space flight combined," Borlaff said.
The researchers used information from satellite operators to simulate the orbital layers of each satellite constellation - from SpaceX's Starlink, China's Guowang and Amazon (AMZN.O), among others. They then considered specific properties of the telescopes such as orbiting altitude, trajectory, field of view and other factors.
"Once we had the simulated telescopes observing our simulated universe, we only needed to count the number of times that the satellites crossed - or 'photo-bombed' - our observatories, and how bright they were at the moment of the event," Borlaff said.
Satellites reflect and emit multiple types of light.
"They directly reflect light from the sun with their solar panels, but also reflect light from the moon and the Earth, which is very intensely bright from low-Earth orbit. In addition to optical light, satellites also emit infrared radiation generated from the temperature of their components, as well as reflecting radio wavelengths from both the Earth and the antennas themselves," Borlaff said.
The researchers said one way to address the problem would be to deploy satellites at orbits lower than where the telescopes operate.
Some telescopes placed at more distant orbits are better shielded from light pollution. The study, for instance, did not look at the effects of the satellites on NASA's James Webb Space Telescope, the European Space Agency's Euclid observatory or NASA's planned Nancy Grace Roman Space Telescope.
Their orbits are much further from Earth than the telecommunications satellites.
"For that reason, they won't likely be affected by this type of contamination, for now," Borlaff said.
These unaffected telescopes provide only a fraction of total astronomical observations, however.
"They are only used for very particular scientific objectives, and have very limited operational time," Borlaff said.
