A defunct man-made satellite the size of a bus is plunging toward Earth, and will likely arrive, breaking up on reentry, by the end of the week.
NASA officials say it's not likely to threaten people on the ground, but they are monitoring the 20-year-old satellite's plunge closely.
The Upper Atmospheric Research Satellite was launched in 1991 and deactivated in 2005 after completing its mission, according to SPACE.com. The vehicle weighs 6.5 tons, but is expected to burn up in the atmosphere.
Donald J. Kessler, a retired NASA scientist, finds concern about falling debris "a little ridiculous," the Los Angeles Times reports.
ABC News has a glimpse of the satellite (or its space shuttle courier, at least), back at the moment of launch in 1991, when it still had years of life and work ahead of it.