What really happens when a Starlink satellite falls back to Earth
The real question scientists are asking is not whether they will fall on your head, but what invisible residue they leave behind in the sky. A five-year life, by design Starlink satellites orbit about 550 kilometers up and are built to last only around five years. Rather than let them linger as dangerous space junk, SpaceX deliberately steers old ones down to burn in the atmosphere, then launches replacements, an endless cycle of launch, deploy, deorbit, repeat. There are already roughly 8,500 Starlink satellites among the 12,000 or so active spacecraft in low orbit, and SpaceX has approval for 12,000 with plans for as many as 42,000. As Harvard-Smithsonian astronomer Jonathan McDowell put it , “There is now a Starlink reentry almost every day.” What burning up leaves behind Satellites are mostly aluminum, and when one plunges back at orbital speed, the heat vaporizes it high in the mesosphere. A typical 250-kilogram satellite generates about 30 kilograms of aluminum oxide nanoparticles as it disintegrates. Multiply that by a near-daily cadence and the numbers add up fast: one study found the amount of aluminum in the upper atmosphere rose eightfold between 2016 and 2022, and it is projected to keep climbing. The ozone question Here is why researchers care. Aluminum oxide acts as a catalyst that can trigger the chemical reactions that destroy ozone, the layer shielding us from harmful ultraviolet light. The particles are not consumed in the process, so a single speck can keep chewing through ozone for decades, and they take up to 30 years to drift down to the altitude where the ozone layer sits. The worry is that this slow accumulation could stall the recovery of the ozone hole, one of the great environmental success stories. The honest caveat: the effect is currently thought to be small, the science is young, and no one has direct measurements yet. As one researcher summed it up, it is not clear the impact will be big enough to be a problem, but it is not clear it won’t be either. For now, mega-constellations amount to a vast, unregulated experiment on the upper atmosphere.
Source: Futura, le média qui explore le monde