A study by the European Southern Observatory warns that plans to launch more than 1.7 million satellites, including large, extremely bright reflectors, could cause serious damage to astronomical observations. The researcher suggests limiting the population of satellites to about 100 and requiring operators to reduce their brightness
Plans to place more than 1.7 million satellites in orbit around Earth satellites May fundamentally change the appearance The night sky and impair the ability of telescopes to explore the universe. This is according to a new study by astronomer Olivier Hino from the European Southern Observatory, ESO.
The study is not just about the bright streaks that satellites leave in astronomical photographs. It also examines a broader phenomenon: sunlight reflected from a huge number of satellites is scattered by the atmosphere and brightens the background of the entire sky. If plans for large satellite arrays and systems of space-based mirrors come to fruition, the result could be light pollution Which will be difficult to escape even in the most distant observatories.
According to the study's conclusions, in order to maintain the possibility of astronomy Modern ground-based, the number of satellites orbiting the Earth should be limited to about 100 and ensure that most of them are too dim to be seen with the naked eye.
Not just a white stripe in the picture
Since then, commercial companies have begun to launch arrays that include thousands Communication satellitesAstronomers struggle with bright streaks that cross photographs of the night sky. With telescopes with a small field of view, it is sometimes possible to discard the affected part of the image or repeat the observation, but with wide-field cameras, the damage can be much more severe.
Astronomical cameras are designed to capture tiny amounts of light from distant stars and galaxies. To do this, they use long exposures and very high sensitivity cameras. A satellite passing through the field of view during the exposure may create a bright streak, flooding the detector with light and even affecting other areas of the image due to electronic effects caused by saturation.
The problem is particularly acute inMitzpe Vera Rubin in Chile, which began its ten-year sky survey in June 2026. The observatory's camera records a large area of the sky with each exposure, so a large number of satellites may appear in its images repeatedly.
In the model, he combined the movement and brightness of the satellites with calculations of light scattering in the atmosphere. In this way, he examined not only the direct damage of the satellite streaks but also their cumulative contribution to brightening the sky.
A million satellites: streaks become almost inevitable
The scenarios examined range from arrays including tens of thousands of dim satellites to a population of about a million satellites or more.
According to the model, an array of about 60 satellites, each dim at a brightness level of 7 at an altitude of about 550 kilometers, would contribute only a tiny fraction to the overall brightness of the night sky. Brightness level 7 is just below the threshold at which a person with normal vision can actually see the sky without any aids.
But even when the satellites themselves are dim, their streaks can interfere with observations. The study estimates that in such an array, satellites could saturate six to 15 percent of the Vera Rubin Observatory camera's field of view under certain conditions.
As the satellite population approaches one million, the streaks become so widespread that it is difficult to find images that are not affected. The problem is not solved by simply using software to erase the streaks, because some of the scientific information behind them is lost, and the effect of the strong light can spread beyond the narrow orbit of the satellite in the image.
Large, bright satellites are especially dangerous
Not all satellites cause the same amount of damage. Large satellites designed to provide direct communications to mobile phones carry very wide antennas and can appear much brighter than regular communications satellites.
The study specifically mentions large satellite arrays such as AST SpaceMobile's BlueWalker and BlueBird. Even though their number is small compared to arrays of tens of thousands of satellites, their size and brightness can create bright spots in photographs and cause saturation in sensitive cameras.
An even more dire scenario involves proposals to place thousands of large mirrors in space. Companies such as Reflect Orbital have proposed using mirrors in orbit to reflect sunlight back to areas of the Earth's surface after sunset.
According to the model, an array of 5,000 such bright reflectors could increase the background brightness of the sky by 20 to 30 percent. An array of 50 mirrors could increase it by 200 to 300 percent—making the night sky up to three times brighter than its natural level.
In such a scenario, it is no longer a matter of individual streaks that one can try to remove from photographs, but rather of brightening the entire sky. Faint and distant objects, from which the light coming from them is very little anyway, may disappear into the bright background.
Even one bright satellite can cause a lot of damage
One important conclusion of the study is that the number of satellites is not the only metric to monitor. A single, particularly bright satellite can cause more damage than thousands of satellites designed to reflect little light back toward the ground.
We would recommend limiting the brightness of most satellites to magnitude 7 or less, and not allowing more than a very small number of brighter satellites to be above the horizon at any one time.
Satellite manufacturers can reduce some of the reflection by changing the shape of the satellite, orienting surfaces, using darker materials, and designing the flight mode so that sunlight is not reflected directly back to the ground. These solutions require cooperation from operators already in the design phase, not just after the satellites have been launched.
In the case of satellites whose stated role is to return light to Earth, reducing the brightness is counterproductive to the purpose of the system itself. For this reason, astronomers argue that it is necessary to examine not only how to reduce the damage, but also whether such systems should be approved in the first place.
Proposal for a ceiling of 100 satellites
The number 100 is not presented in the study as a sharp and absolute natural limit. According to Heino, at this level the rate of astronomical data loss would be roughly similar to the losses caused today by technical and weather reasons.
Furthermore, satellite accumulation could become a major and permanent factor in the loss of observation time. This number is still much larger than the population of currently operational satellites, but it is very small compared to the more than 1.7 million satellites included in various proposals and launch plans.
The study highlights that near-Earth space is not an unlimited resource. In addition to harming astronomy, the proliferation of satellites increases orbital congestion, the risk of collisions, and the amount of objects that will eventually re-enter the atmosphere.
The debate doesn’t have to end with a choice between satellite communications and astronomy. We can design dimmer satellites, limit extremely large arrays, and require operators to provide precise orbit data to observatories. But without binding international rules, each company has an incentive to launch quickly before its competitors grab the coveted orbits and frequencies.
If more than a million satellites and mirrors are actually deployed around Earth, the damage won't just be to beautiful photographs of the night sky. Astronomers could lose the ability to detect dangerous asteroids, track variable stars, detect supernovae, and study faint galaxies from the early universe.
The night sky is part of humanity's scientific and cultural heritage. The new study warns that without limits on the number, size and brightness of satellites, we could change it in a few years in ways that cannot be easily fixed.
The scientific article
“Large or bright satellite constellations: Effects on observations, including on the background sky brightness”, by Olivier R. Hainaut. Pre-publication on arXiv, April 2026. ([arXiv][1])
For the scientific article: Opening the scientific article
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2 תגובות
If launching a satellite into space becomes relatively cheap and available – it seems to me that it makes much more sense.
It also means sending a lot of telescope satellites into space instead of those on Earth.
You don't need the most sophisticated one like Hubble and the like, the telescope itself costs millions or billions.
Any telescope used on Earth that is reasonably priced and simpler can also be simply launched into space. Wrap it in a communications satellite – which will stream the data from it to Earth.
Population is a term that refers to a group of people, animals, or plants, not objects.