Mega-satellite constellations pose danger to night sky, warns ESO

The European Southern Observatory (ESO) has issued a stark warning about the potential "devastating consequences" of mega-satellite constellations on the night sky. A new study by the ESO, published in Astronomy & Astrophysics, suggests that the growing number of satellites could severely hamper astronomical observations.

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When a satellite passes in front of what we are observing, it leaves a bright trail on our image, obscuring everything behind it.

The study highlights that the number of satellites orbiting Earth has rapidly increased since 2019, with SpaceX's Starlink constellation being a major contributor. Projections indicate that over 1.7 million satellites could eventually orbit the planet, a figure that deeply concerns astronomers.

"When a satellite passes in front of what we are observing, it leaves a bright trail on our image, obscuring everything behind it," explained Olivier Hainaut, an ESO astronomer and lead author of the study. While current satellite passes are manageable, a dramatic increase in numbers would create significant problems. Hainaut is particularly worried about satellites designed to be extremely bright.

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If we go from 14,000 to 1.7 million, we will really have problems.

Even satellites not directly pointed at observers could become problematic. Projects like Reflect Orbital aim to launch up to 50,000 large, mirror-like satellites by 2035 to provide nighttime illumination via reflected sunlight. These could appear as numerous as "thousands of Venuses" in the sky, comparable to the brightness of the planet Venus. The ESO study emphasizes that this would eliminate the possibility of a truly dark, pristine night sky, even in remote natural locations, making the night sky resemble that seen from a city's outskirts.

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Whether in Auvergne, the Sahara, or the Atacama Desert, the sky we would see would no longer be a pure sky, but would resemble the one we see from the outskirts of a city.