Most satellites have propulsion systems - both to tweak their orbits, and to help adjust their orientation in space. "Decommissioned" does not mean that all th

Most satellites have propulsion systems - both to tweak their orbits, and to help adjust their orientation in space. "Decommissioned" does not mean that all the pressurized tanks for those propulsion system are empty, nor de-pressurized. And as any aerospace materials engineer knows, things degrade over time... BTW - the chemicals in those propulsion tanks are often quite nasty, and prone to "energetic" reactions.