NASA study shows how satellite ‘light pollution’ hinders space telescopes

By Will Dunham

WASHINGTON, Dec 3 (Reuters) – The exponential increase in the number of satellites placed in low Earth orbit has enabled advances in telecommunications, including broadband access to rural and remote areas around the world. It has also caused an increase in light pollution in space that jeopardizes the work done by orbiting astronomical observatories.

A new NASA study of four space telescopes – two currently operational and two planned – estimates that a significant percentage of the images obtained by these observatories over the next decade could be altered by light emitted or reflected by satellites sharing their low Earth orbit.

Researchers calculated that about 40% of images taken by NASA’s Hubble Space Telescope and about 96% of those taken by the US 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 because of its narrow field of view, the researchers said.

Orbiting telescopes are an essential part of space exploration. They can observe a wider range of the electromagnetic spectrum than ground-based telescopes, and the lack of atmospheric interference allows them to obtain sharper images of the cosmos, enabling direct imaging of distant galaxies or planets “beyond our solar system.”

“While until now most light pollution has come from cities and vehicles, the rise of telecommunications satellite constellations is quickly beginning to affect astronomical observatories around the world,” said astronomer Alejandro Borlaff of NASA Ames Research Center in California, lead author of the study published in the journal Nature.

“As telescopes observe the universe trying to unveil distant galaxies, planets and asteroids, satellites sometimes cross in front of their cameras, leaving light trails that blot out the faint signal 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 seemingly pristine vantage points in space – were considered almost free of original light pollution human,” Borlaff said.

As of 2019, there are approximately 2,000 satellites in low Earth orbit. Their number now stands at around 15,000 ‌. Borlaff said industry proposals call for about 560,000 satellites in low Earth orbit over the coming decade.

“To give an idea of ​​the recent increase in this number, we have launched more satellites into low Earth orbit in the last four years – 2021 to 2025 – than in the previous seven decades of spaceflight combined,” Borlaff said.

The researchers used information from satellite operators to simulate the orbital layers of each satellite constellation – SpaceX’s Starlink, China’s Guowang and Amazon, among others. They then looked at specific properties of the telescopes such as orbital altitude, trajectory, field of view and other factors.

“Once we had the simulated telescopes observing our simulated universe, we just had to count the number of times the satellites passed through – or ‘photo-bombed’ – our observatories, and how bright they were at the time of the event,” Borlaff said.

Satellites reflect and emit several types of light.

“They reflect sunlight directly with their solar panels, but also reflect light from the Moon and Earth, which is very intensely bright from low Earth orbit. In addition to optical light, satellites also emit infrared radiation generated by the temperature of their components, as well as reflect radio wavelengths from Earth and the antennas themselves,” Borlaff said.

The researchers said one way to solve the problem would be to deploy satellites in lower orbits than where telescopes operate.

Some telescopes placed in more distant orbits are better protected from light pollution. The study, for example, did not examine the effects of satellites on NASA’s James Webb Space Telescope, the European Space Agency’s Euclid Observatory or NASA’s Nancy Grace Roman Space Telescope project.

Their orbits are much further from Earth than those of telecommunications satellites.

“For this reason, they probably won’t be affected by this type of contamination at this time,” Borlaff said.

These unassigned telescopes, however, provide only a fraction of the total astronomical observations.

“They are only used for very specific scientific purposes and have a very limited operating life,” Borlaff said.

(Reporting by Will Dunham, editing by Rosalba O’Brien)