The satellite in question is a Russian space probe called Phobos-Grunt. Designed to grab and return with a surface sample of Phobos (one of Mars’ moons), it encountered trouble soon after its initial launch on November 8, 2011. The rocket system that would have taken it to Mars malfunctioned, leaving it stranded in a low Earth orbit. Since then, all attempts to communicate with the probe have failed, and the entire thing is destined to plunge to Earth in the coming days.
The final architecture of the Phobos-Grunt spacecraft and its major components as of 2011.
Unfortunately, because Phobos-Grunt was supposed to go to all the way to Mars, it retains a full payload of highly toxic rocket fuel. The good news is that almost all of the satellite is expected to burn up in the atmosphere, including the fuel. Only a couple of dozen fragments are expected to survive reentry.
We don’t yet know exactly when or where the satellite will land, but an early estimate puts it over the Indian Ocean on Sunday afternoon.