Despite the incredible achievements of space telescopes, both old and new, the vast majority of astronomy is done on the ground. And scientists, stakeholders, and people who just love the night sky have become concerned about the increase in the number of satellites that now populate low-earth orbit. Now, astronomers have provided an estimate of their impact on images captured by the Zwicky Transient Facility (ZTF), an instrument that operates from Caltech's Palomar Observatory near San Diego.
The findings are published in The Astrophysical Journal Letters and focus on SpaceX’s StarLink. These satellites reflect sunlight at dawn and dusk, twinkling, and creating streaks in the images – almost one in five images taken at twilight show satellite streaks. These observations are mostly used to pick up Near-Earth Orbit asteroids.
Over the last few years, Elon Musk’s SpaceX has aimed to build a network of satellites to bring internet access worldwide. The megaconstellation is now comprised of around 1,800 satellites and provides internet service to 24 of almost 200 countries around the world. By 2027, Musk expects 10,000 satellites in orbit, and that means that virtually all twilight images from ZTF will have satellite streaks on them.
"In 2019, 0.5 percent of twilight images were affected, and now almost 20 percent are affected," lead author Dr Przemek Mróz, from the University of Warsaw in Poland, said in a statement. "We don't expect Starlink satellites to affect non-twilight images, but if the satellite constellation of other companies goes into higher orbits, this could cause problems for non-twilight observations."
Currently, the satellites affect about 0.1 percent of the pixels in the images taken at twilight. Astronomers believe that software solutions could help in a number of ways, from avoiding catching satellites in views to assessing which observations were affected, and even to masking or reducing the negative effects.
Some people online have raised the point that it shouldn’t be up to publicly funded bodies to come up with this kind of software. After all, the problem was created by a private company owned by the richest man in the world – who got even richer during the pandemic – perhaps he should be solving it.
The solution that SpaceX has been employing has been to equip the satellites with visors. The change, which began in 2020, proved to be effective, reducing their brightness by 4.6 times, below what can be seen with the naked eye but still too bright with respect to astronomers' recommendations.
The team stresses that this is specific to ZTC. More sensitive instruments such as the upcoming Vera C. Rubin Observatory, under construction in Chile, are likely to be more affected by them.
These megaconstellations also affect space exploration and astronomy. It was revealed by the European Space Agency’s Director General that during the 30 minute launch window for JWST, a few minutes were not usable due to the presence of StarLink satellites. And, twice, satellites have come too close to Tiangong, the Chinese Space Station, according to the Chinese National Space Agency.