What happens to the old satellites and other debris that is left in space? Why is it even acceptable to leave our trash / garbage out there?
Once something is in space, there's only a few ways it'll ever come back down.
- It rockets down to re-enter Earth
- It is in the upper part of the atmosphere, which slowly will bring it down.
- Sunlight pushes it into an orbit where it intersects the atmosphere, or even leaves Earth orbit.
- It hits another object, changing it's velocity.
Once debris is up there, it's hard to get down. Spacecraft are required to put themselves into either a graveyard orbit, or an orbit where the spacecraft will naturally return to Earth shortly thereafter. However, some spacecraft fail, others were built before this was a known problem, and overall, it's expensive to ensure that it happens.
Currently there are thousands to millions of objects orbiting around earth's surface. These items are just as "acceptable" as Saturn's rings. Whether everything will stay there or come down to earth depends on the object.