People from New Mexico to Montana saw the bright object break apart as it moved slowly northward across the night sky. Witnesses described it as three "rocks" with glowing red and orange streaks.
But the fireball that blazed over the Rockies earlier this month wasn't a meteor or other celestial body, experts said. Instead, it likely was part of a Russian spy satellite that fell from orbit and burned up over Colorado and Wyoming.
More than three dozen witnesses filed reports about the unusual sighting, which happened around 10:30 p.m. MDT on Sept. 2. Here are some more details on it:
How do experts know the object was a satellite?
A meteor would have burned too quickly to be seen over such a vast area, said Mike Hankey, the American Meteor Society's operations manager. He added that fragments from the object were even big enough to show up as a weather event on radar just east of Cheyenne, Wyoming.
The object probably was a piece of Russia's Cosmos 2495 reconnaissance satellite, launched in May, said Charles Vick, an aerospace analyst with military information website Globalsecurity.org. Kosmos 2495 was designed to shoot reconnaissance photos and send the film back to Earth in capsules.
What happened to the spy satellite?
It delivered film to Russia as intended, but some pieces of the craft remained in orbit until falling over the Rockies, Vick said.
The U.S. Strategic Command, responsible for American nuclear warfighting forces, confirmed that Kosmos 2495 re-entered the atmosphere and was removed from the U.S. satellite catalogue Sept. 3.
So are Russian spy satellites still monitoring U.S. military installations?
Yes. They're basically spying on the same things they kept an eye on during the Cold War, said John Pike, director of Globalsecurity.org. "Deployed hardware, airplanes, ships, tanks, factories, new intelligence facilities, all that stuff," he said.
The satellites are looking for targets for their nuclear weapons, Pike said. "They're looking for the same things that our spy satellites are looking for."
How many spy satellites are out there?
Jonathan McDowell, an astronomer with the Harvard-Smithsonian Center for Astrophysics, estimates that there are 98 operating spy satellites in orbit, launched by at least six nations.
Of those, 37 are from the United States, 30 from China and just three from Russia, he said. Many of those satellites are old, and probably half are in full operation, McDowell said.
Gen. William L. Shelton, former head of the U.S. Space Command, has said about 1,100 satellites orbit the Earth, and the U.S. Defence Department operates fewer than 100.
Russia has more than 100 satellites — including reconnaissance, weather and communications.
What do the Russians say about this month's event?
Their military satellites have been operating normally, a Russian Defence Ministry spokesman told the ITAR-TASS news agency Sept. 9.
"One can only guess about the condition representatives of the so-called American Meteor Society were in when they identified a luminescent phenomenon high up in the sky as a Russian military satellite," said the spokesman, Igor Konashenkov.