Russia's failed Mars probe, Phobos-Grunt, is expected to fall back to Earth this weekend.
The satellite was launched into space last November on a mission to bring back soil samples from the Red Planet's largest moon.
But it was stranded around Earth's orbit and is now about to re-enter the atmosphere.
The BBC's science correspondent says most of the 13-tonne satellite will burn up on re-entry, but some debris could reach the surface of the Earth.
The location is uncertain. It could be either the Atlantic Ocean or the Pacific Ocean.
