A 20-year-old space satellite is heading back down to Earth, but scientists don't know where it's going to land.
It was sent up in 1991 by the American space shuttle Discovery, but it's been out of action for the last six years.
Gravity is now dragging it back, but luckily most of the six-tonne satellite will burn up before reaching Earth.
26 parts of it could survive though and the space agency Nasa is trying to track its route.
It's expected to land on Earth on Friday evening, but as it's travelling fast and tumbling down unpredictably, Nasa won't know where it will land until about two hours before.
But don't worry, Nasa says that no-one has ever been hurt by objects falling from space, and the chances of anyone being hit are about one in 3,000 - so it's very unlikely.