A new listing of the 50 most concerning pieces of space debris in low-Earth orbit is dominated by relics more than a quarter-century old, primarily dead rockets left to hurtle through space at the end of their missions. “Seventy-six percent of the objects in the top 50 were deposited last century, and 88 percent of the objects are rocket bodies. In the paper, analysts considered how close objects are to other space traffic, their altitude, and their mass. If someone sent missions to retrieve all 50 of the objects, the overall debris-generating potential in low-Earth orbit would be reduced by 50 percent, according to McKnight. The 25-year discriminator is important because that is the guideline promulgated by the Inter-Agency Space Debris Coordination Committee, an international group that includes representatives from all of the major space powers: the United States, China, Russia, Europe, India, and Japan.