The 6.5 ton UARS satellite has been orbiting Earth since 1991, and it's now headed back in an uncontrolled fall. NASA isn't sure exactly when, and they're not sure exactly where, but over 1,000 pounds of ex-satellite could make it through the atmosphere to your front lawn. Um, duck?
UARS stands for "Upper Atmosphere Research Satellite," which is fitting since it was a satellite designed to research the upper atmosphere. Discovery released it back in 1991, and UARS operated for nearly 15 years, keeping a tidy record of all the terrible things we're doing to the ozone layer. Shortly before its 2005 decommissioning, UARS made one final engine burn designed to gradually lower its orbit, and after spiraling down for the last six years (and narrowly missing the ISS on the way), the satellite will be reentering the atmosphere. Like, soon. Probably.
NASA is having trouble pinpointing the exact time of reentry because they don't know how the satellite is currently oriented in space, and how fast it slows down depends on how much resistance it gets from incoming solar radiation. If UARS is pointed directly into this solar flux, it'll last longer than if it's side-on. NASA is tracking UARS very closely, though, and they should know four or five days ahead of time about when it's going to come down. At that point, they should be able to estimate a 500 mile swath in which the 1,170 pounds (ish) of surviving debris will land. Right now, all they know is that it could be anywhere between 57 degrees north and 57 degrees south of the equator, which covers basically the entire populated planet with the exception of Scandinavia and Sibera.
It's quite unlikely that the charred remains of UARS will hurt anyone or cause any damage, but just in case, NASA has thoughtfully provided the following words of wisdom:
"If you find something you think may be a piece of UARS, do not touch it. Contact a local law enforcement official for assistance."
Or you can call us, and we'll totally come take care of it for you.