Astronaut spots UFO outside space station — but then it's identified

NASA astronaut Chris Cassidy alerted ground controllers on Monday to an unidentified flying object floating near the International Space Station — but this was no alien spacecraft.

Instead, it was a piece of the station itself: Russian ground controllers identified it as an antenna cover from the Zvezda service module, one of the oldest parts of the station.

The sighting merited just a brief mention in NASA's latest space station status report, plus a short clip on NASA's YouTube channel. Because the antenna cover's speed in relation to the rest of the station was so low, it didn't pose that much of a collision hazard. But controllers were glad to see the debris fade off into the distance, heading for what they expected would be a brief, fiery re-entry in the atmosphere.

This wasn't the first station debris to cause a UFO stir: Back in 1998, during the shuttle Endeavour's mission to hook the U.S.-built Unity connecting node to the Russian-made Zvezda module, astronauts spotted a blobby object floating away from the scene. NASA determined that the object was a discarded thermal cover, but that didn't stop UFO fans from working the material into their tale of a mysterious "Black Knight" satellite that has been circling our planet for millennia.

More UFO lore:

Alan Boyle is's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.