In the next decade, almost all images taken by NASA and ESA space telescopes in Earth orbit could be disrupted or unusable by light pollution from surrounding satellites, a simulation shows. Accordingly, light pollution from satellites in orbit must be minimized in order to be able to carry out successful astronomical research. It is still unclear how this can be achieved.
There are more and more artificial satellites in orbit around the Earth. While there were around 2,000 in 2019, there are now around 15,000 satellites orbiting Earth. This rapid increase was made possible because the costs of launching a rocket into space have fallen. This makes satellite constellations such as Starlink, which provide broadband Internet via orbit, worthwhile. And the trend continues: Based on a database of planned satellite launches, it is predicted that there could be as many as 560,000 satellites in orbit in around ten years. These are needed, among other things, for telecommunications and navigation on Earth as well as for observing the weather, climate, environment and military situation on our planet.
There are also observatories in Earth’s orbit, such as NASA’s Hubble Telescope, which astronomers use to look in the other direction and explore the cosmos. To do this, they continuously take images of space. However, these images can be disturbed by sunlight reflected from the shiny surfaces of the surrounding satellites. This light pollution often makes the telescope images unusable because the satellites leave bright streaks or distracting scattered light in them. Around four percent of the images created by the Hubble Space Telescope between 2018 and 2021 already showed such satellite tracks.
Space telescopes could hardly take usable images anymore
Researchers led by Alejandro Borlaff from the NASA Ames Research Center have now investigated how large the disruptive effects of orbital light pollution will be for space telescopes in the future as the number of satellites increases. To do this, they simulated the future view of four space telescopes – the existing NASA telescopes Hubble and SPHEREx, the ARRAKIHS telescope planned by ESA for 2030 and the Chinese Xuntian telescope planned for 2026. These space observatories are located or will be stationed in orbits between 400 and 800 kilometers altitude. They orbit in low Earth orbit, a zone particularly densely populated with satellites.
The simulation found that if there were 560,000 satellites in orbit in the 2030s, their scattered light would affect 40 percent of the images taken by Hubble and 96 percent of the images taken by the other three telescopes. The reflected light from an average of two satellites will then disturb the images in Hubble’s field of vision per recording; at SPHEREx there are almost six satellites at ARRAKIHS 69 and at Xuntian 92. If there are even a million satellites in Earth orbit, the images from the telescopes would be disturbed on average by four (Hubble), nine (SPHEREx), 127 (ARRAKIHS) and 165 (Xuntian) satellites. Accordingly, space telescopes would hardly be able to take usable images in the future.
Should satellites fly lower?
Tried-and-tested optical blockers and black coatings on satellite surfaces have proven inadequate to prevent light reflection. As an alternative solution to this problem of space exploration, Borlaff and his colleagues suggest deploying satellites into lower orbits in the future so that they operate below astronomers’ telescopes. However, this approach carries the risk that emissions from these satellites will disrupt the Earth’s ozone layer. It would therefore be better to generally use fewer satellites in order to be able to continue exploring space. For the two telescopes that are still being planned, the team also recommends adapting their design so that the viewing angle is disturbed by as little scattered light as possible.
Source: Alejandro Borlaff (NASA Ames Research Center) et al.; Nature, doi: 10.1038/s41586-025-09759-5