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The study considered the tens of thousands of objects in orbit as of 2020—before an onslaught of thousands more satellites that companies plan to launch in the coming years.
“It’s a bit of an eye-opener,” says John Barentine, director of public policy at the International Dark-Sky Association, who helped author the study, accepted today in Monthly Notices of the Royal Astronomical Society and posted online.
He wondered whether the collective cloud of satellites and debris above Earth might scatter light back into the atmosphere more generally.
Even if the individual objects aren’t visible, could their presence add an additional background glow to the night sky in a way that would wash out the faintest reaches of the cosmos?.
Even at the darkest possible sites on Earth, the sky itself has a natural glow in the upper atmosphere from sources like ionized particles.
But on top of that background glow, objects already in orbit may add about 10% more diffuse light, they estimate.
“I look forward to an independent confirmation of the result,” says Pat Seitzer, an emeritus astronomer at the University of Michigan, Ann Arbor, who has modeled the brightness of individual satellites and is collaborating with SpaceX to dim future versions.
In 1979, the International Astronomical Union suggested astronomical observatories should be built only where light pollution adds less than 10% more light over natural skyglow; the new study suggests nowhere on the planet meets those standards anymore.
But it could matter to astronomers searching for faint, sprawling objects on the sky such as dim galaxies, which astronomers are studying for clues to the physics of galaxy formation and the nature of dark matter.
What matters most for this kind of research is not just the amount of added background glow but how it varies across the globe—neither of which has yet been actually measured, says Mireia Montes, an astronomer at the Space Telescope Science Institute.