Reentry of NASA satellite will exceed the agency's own risk guidelines

A NASA satellite that spent more than a decade coursing through the Van Allen radiation belts encircling Earth is about to fall back into the atmosphere.

Most of the spacecraft will burn up during reentry, but a fraction of the material making up the 1,323-pound (600-kilogram) satellite will likely reach Earth's surface without vaporizing in the atmosphere. Uncontrolled reentries of satellites with comparable mass happen quite regularly—multiple times per month, according to one recent...