As Earth Warms, Its Outer Atmosphere Shrinks; This Shrinks Useable Satellite Space, Already Filled With Orbiting Junk
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All the excess carbon dioxide generated by people burning fossil fuels is shrinking the upper atmosphere, exacerbating the problem with space junk. New research, published in Nature Sustainability on Monday, found that if emissions don’t fall, as few as 25 million satellites — about half the current capacity — would be able to safely operate in orbit by the end of the century. That leaves room for just 148,000 in the orbital range that most satellites use, which isn’t as plentiful as it sounds: A report from the U.S. Government Accountability Office in 2022 estimated that as many as 60,000 new satellites will crowd our skies by 2030. According to reports, Elon Musk’s SpaceX alone wants to deploy 42,000 of its Starlink satellites.
“The environment is very cluttered already. Satellites are constantly dodging right and left,” said William Parker, a Ph.D. researcher in the Massachusetts Institute of Technology’s Department of Aeronautics and Astronautics and the lead author of the study. In a recent six-month period, SpaceX’s Starlink satellites had to steer around obstacles 50,000 times. “As long as we are emitting greenhouse gases, we are increasing the probability that we see more collision events between objects in space,” Parker said.
Until recently, the effects of greenhouse gas emissions on the upper atmosphere were so understudied that scientists dubbed it the “ignorosphere.” But research using modern satellite data has revealed that, paradoxically, the carbon dioxide that warms the lower atmosphere is dramatically cooling the upper atmosphere, causing it to shrink like a balloon that’s been left in the cold. That leaves thinner air at the edge of space. The problem is that atmospheric density is the only thing that naturally pulls space junk out of orbit. Earth’s atmosphere doesn’t suddenly give way to the vacuum of space but gets dramatically thinner at a point known as the Kármán line, roughly 100 kilometers up. Objects that orbit the planet are dragged down by the lingering air density, spiraling closer to the planet until eventually reentering the atmosphere, often burning up as they do.
According to the nonprofit Aerospace Corporation, the lowest orbiting debris takes only a few months to get dragged down. But most satellites operate in a zone called “low Earth orbit,” between 200 and 2,000 kilometers up, and can take hundreds to thousands of years to fall. The higher outermost reaches of Earth’s influence are referred to as a “graveyard” orbit that can hold objects for millions of years. “We rely on the atmosphere to clean out everything that we have in space, and it does a worse job at that as it contracts and cools,” Parker said. “There’s no other way for it to come down. If there were no atmosphere, it would stay up there indefinitely.”
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https://grist.org/science/space-junk-greenhouse-gases-satellites/