Explosion of satellites could transform the night sky, study warns

UA new study by the European Southern Observatory (ESO) warns of the risk of an unprecedented increase in the number of satellites in orbit. According to the research, projects currently under analysis foresee the launch of more than 1.7 million new satellites, including extremely bright models capable of altering the appearance of the night sky and disrupting astronomical observations.

The work, led by Belgian astronomer Olivier Hainaut, from ESO, calculates for the first time the impact of large constellations of satellites on the luminosity of the sky. The researchers’ concern is that this excess of objects in orbit will hamper the work of telescopes used to study distant galaxies, Earth-like planets outside the Solar System and asteroids that could pose a risk to the planet.

Currently, there are more than 14 thousand active satellites around the Earth. The number rises to around 32 thousand when inactive satellites and fragments of space objects are considered.

The scenario could change drastically in the coming years. According to the study, SpaceX, Elon Musk’s company, intends to launch around 1 million new satellites aimed at data centers in space. For Hainaut, a constellation of this size would significantly change the appearance of the sky.

Simulations indicate that hundreds of satellites could be seen throughout much of the night. At times, this number could reach thousands, a quantity similar to the total number of stars visible to the naked eye under good observation conditions.

Another company mentioned in the survey is the North American Reflect Orbital, which plans to launch up to 50,000 satellites by 2035. The proposal involves equipment similar to mirrors, capable of reflecting sunlight back to Earth at night. The beams of light could reach areas of at least five kilometers on the planet’s surface.

According to Hainaut, if this constellation is placed into orbit, hundreds of very bright satellites could be seen in the night sky. When observed from the region illuminated by the reflected beam, these objects would appear four times brighter than the full Moon. Even outside the direct focus of the light, each satellite could have a brightness similar to that of Venus.

The study states that, in a city already marked by light pollution, such as Munich, Germany, these satellites could become the only “stars” visible in the night sky.

In addition to the light trails left in telescope images, researchers warn of another effect: the general increase in sky brightness. Even barely visible satellites can contribute to a kind of veil of diffuse light, while brighter objects spread luminosity throughout the atmosphere.

In the case of a complete constellation with 50,000 Reflect Orbital satellites, the night sky could become three to four times brighter, according to simulations.

To calculate these impacts, Hainaut simulated the position, movement and brightness of current and future satellite constellations. The study took into account observations made with instruments such as ESO’s Very Large Telescope and the Vera C. Rubin Observatory, both in Chile.

The astronomer claims that satellites illuminated by the Sun are much brighter than distant galaxies. When they pass in front of the field observed by a telescope, they leave intense traces in the images and can erase important information about the objects studied.

ESO also draws attention to impacts beyond astronomy. Light pollution caused by very bright satellites can interfere with biological clocks and ecosystems. Large constellations also require many launches and can affect air quality, both through emissions associated with missions and through the burning of equipment when reentering the atmosphere at the end of its useful life.

For the author of the study, the only way to avoid serious damage to terrestrial astronomy would be to limit the total number of satellites in orbit. Hainaut argues that no more than 100,000 weak satellites, invisible to the naked eye, should circle the Earth.

According to him, this limit is not an absolute number, but a reference to keep losses in astronomical observations at levels similar to those from common technical failures. If the satellites are brighter, the acceptable total would have to be even lower.

The research was accepted for publication in the scientific journal Astronomy & Astrophysics.