A large, defunct satellite spiraling out of orbit and back to Earth will reenter the atmosphere sometime this afternoon or evening tonight or tomorrow morning Eastern Daylight Time has reentered the atmosphere, NASA says.* The 5.7-metric-ton Upper Atmosphere Research Satellite, which descended uncontrolled, was expected to drop some 500 kilograms of debris somewhere on Earth, although the chances of harm to human life were slim. NASA's chief scientist for orbital debris said two weeks ago that an object the size of UARS falls out of orbit about once a year and that no one has ever sustained a confirmed injury from falling space junk.

NASA's most recent update to UARS's status came just after 10:00 PM EDT last night. At that time, the space agency noted that the satellite would not reenter over North America but that it was "still too early to predict the time and location of re-entry with any more certainty."

We will update this page as more information on UARS becomes available.

* UPDATE (11:00 A.M.): The headline and first sentence of this blog post have been updated to reflect new information from NASA: "The satellite’s orientation or configuration apparently has changed, and that is now slowing its descent. There is a low probability any debris that survives reentry will land in the United States, but the possibility cannot be discounted because of this changing rate of descent."

*UPDATE (September 24, 2011): The headline and first paragraph of this blog have been updated to reflect new information. NASA says that UARS fell back to Earth between 11:23 P.M. Friday and 1:09 A.M. EDT today. But a precise landing area has not been confirmed, according to the space agency: "The Joint Space Operations Center at Vandenberg Air Force Base in California said the satellite penetrated the atmosphere over the Pacific Ocean. The precise re-entry time and location are not yet known with certainty."